Tag Archive | "silicon"

Project Review – Silicon Chip Capacitance Substitution Box


Every month Australian electronics magazine Silicon Chip publishes a variety of projects, and in some cases various (well … one of two) electronics retailers will pick up the project and offer it as a kit. However for an increasing number of new projects they don’t, which leaves the interested reader with one option – build the entire project from scratch.

But thankfully this is no longer the case – as the team from Silicon Chip now offer a range of project PCBs and matching front panels for sale directly from their website. Although buying these parts is not the cheapest option, it gives the busy person who likes making things a quick start – or the inexperienced more opportunities to complete a successful project.

So as a test of this new service, I bought the PCB and front panel for the Capacitance Substitution Box project described by Nicholas Vinen in the Juily 2012 issue of SC:


This is something I’ve meant to make for a while – but didn’t really have the inclination to make one from scratch, so it was neat to see a version published in the magazine. I believe the subjects in the magazine article are oftern prototypes, which explains the difference in colour for the front panel.

The parts arrived in a week after placing the order, and are of a high quality:

capacitance box panel

capacitance pcb front

capacitance pcb rear

When complete, the capacitance substitution box PCB and panel will fit nicely into an Altronics H0151 enclosure, so you don’t need to do any drilling or filing. The next task was to organise the required parts. The rotary switches, terminal posts and the usual odds and ends can be found at Altronics, Jaycar or other suppliers. However the main components – the capacitors – offered two options.

The first option is to simply use capacitors from personal stock or the stores. However the tolerance of these parts can vary wildly, with up to twenty percent either way. This is ok for simple uses, however when values are combined – the tolerance of larger values can negate the lower values completely. So instead I’ve chosen the second option – which involves using brand-name low-tolerance capacitors.

Thus I turned to element14 who stock not only a huge range of not only regular but also the low-tolerance capacitors, and can also have them on my desk usually by the next working day. Finally, it’s nice to have all the parts arrive in little bags… neatly organised ready to go:


It’s easy to search for low-tolerance parts with element14, as the automatic filtering has tolerance as a parameter:

element14 capacitors

Furthermore you can also ensure you have the voltage rating of at least 50V DC as well. So after half an hour the capacitor order was completed and arrived when expected – using parts from Panasonic, Vishay, and Wima. The tolerances of our capacitors used varied between one and ten percent, which will help improve the accuracy of the substitution box.


The PCB has the capacitor values labelled neatly on the silk-screen, so soldering in all the capacitors was a relatively simple but long operation. Having them arrive in separate packets made life a lot easier. During the soldering process it’s a good idea to have a  break or two, which helps you avoid fatigue and making any mistakes.

capacitance substitution box half finished

There may be a few capacitors that are a little too wide to fit with the others, so they can be mounted on the other side of the PCB:

capacitance substitution box wide capacitor

However they all end up fitting well:

capacitance substitution box half finished

The next step was to configure the first rotary switch for six position use, then cut the plastic stopped from the side of each rotary switch. In the following image you have a before and after example:

capacitance substitution box rotary switches

Now the rotary switches can have their shafts trimmed and then be soldered onto the PCB:

capacitance substitution box switches trimmed

However ensure you have the first rotary switch in the right way – that is the selections are selected across the top half, not the bottom. Remove the nuts from the rotary switches, and double-check all the capacitors are fitted, as once the next step is completed … going back will be difficult to say the least.

At this point the banana sockets can be fitted to the panel, and then soldered into place, and then you’re finished. Just place the panel/PCB combination inside the box and screw it down:

capacitance substitution box complete

Using the Capacitance Substitution Box

Does it work? Yes – however you don’t get exact values, there will always be a tolerance due to the original tolerance of the capacitors used and the stray capacitance of the wires between the box and the circuit (or capacitance meter). Nevertheless our example was quite successful. You can see the box in action with our Altronics LC meter kit in this video.

Again, using the best tolerance capacitors you can afford will increase the accuracy of this project.


Over time this would be a useful piece of equipment to have – so if your experiments or projects require varying capacitor value, this project will serve the purpose nicely. Plus it helps with mental arithmetic and measures of capacitance! Please do not ask me for copies of the entire Silicon Chip article, refusal may offend. Instead – visit their website for a reprint or digital access.

And if you enjoyed this article, or want to introduce someone else to the interesting world of Arduino – check out my book (now in a third printing!) “Arduino Workshop”.

visit tronixlabs.com

Have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column, or join our forum – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in capacitor, kit review, projects, silicon chip, substitution box

Kit Review – Altronics/Silicon Chip ISD2590 Digital Message Recorder


Every month Australian electronics magazine Silicon Chip publishes a variety of projects, and in February 1994 they published the “90 Second Digital Message Recorder” project. That was a long time ago, however you can still find the kit today at Altronics (and at the time of writing, on sale for AU$26), and thus the subject of our review.

The kit offers a simple method of recording and playing back 90 seconds of audio, captured with an electret microphone. When mounted in a suitable enclosure it will make a neat way of leaving messages or instructions for others at home.


The kit arrives in typical Altronics fashion:

Altronics K9570 90 second message recorder kit package

… and includes everything required including IC sockets for the ISD2590 and the audio amplifier:

Altronics K9570 90 second message recorder kit inclusions

Altronics K9570 90 second message recorder kit components

The PCB missed out on silk-screening – which is a pity:

Altronics K9570 90 second message recorder kit instructions PCB front

however it is from an original design from twenty years ago. The solder mask is neat and helps prevent against lazy soldering mistakes:

Altronics K9570 90 second message recorder kit PCB back

Finally the detailed instructions including component layout and the handy Altronics reference guide are also included. After checking and ordering the resistors, they were installed first along with the links:

Altronics K9570 90 second message recorder kit construction

 If you have your own kit, there is a small error in the instructions. The resistor between the 2k2 and the 10uF electrolytic at the top of the board is 10k0 not 2k2. Moving on, these followed by the capacitors and other low-profile components:

Altronics K9570 90 second message recorder kit construction 4

The rest of the components went in without any fuss, and frankly it’s a very easy kit to assemble:

Altronics K9570 90 second message recorder kit finished

 The required power supply is 6V, and a power switch and 4 x AA cell holder is included however were omitted for the review.

How it works

Instead of some fancy microcontrollers, the kit uses an ISD2590P single chip voice recording and playback IC:

Altronics K9570 90 second message recorder kit ISD2590

It’s a neat part that takes care of most of the required functions including microphone preamp, automatic gain control, and an EEPROM to store the analogue voltage levels that make up the voice sample. The ISD2590 samples audio at 5.3 kHz which isn’t CD quality, but enough for its intended purpose.

Apart from some passive components for power filtering, controls and a speaker amplifier there isn’t much else to say. Download the ISD2590 data sheet (pdf), which is incredibly detailed including some example circuits.


Once you apply power it’s a simple matter of setting the toggle switch on the PCB down for record, or up for playback. You can record in more than one session, and each session is recorded in order until the memory is full. Then the sounds can be played back without any fuss.

The kit is supplied with the generic 0.25W speaker which is perhaps a little weak for the amplifier circuit in the kit, however by turning down the volume a little the sound is adequate. In this video you can see (and hear) a quick recording and playback session.


This kit could be the base for convenient message system – and much more interesting than just scribbling notes for each other. Or you could built it into a toy and have it play various tunes or speech to amuse children. And for the price it’s great value to experiment with an ISD2590 – just use an IC socket. Or just have some fun  – we did.  Full-sized images are available on flickr

And if you enjoyed this article, or want to introduce someone else to the interesting world of Arduino – check out my book (now in a third printing!) “Arduino Workshop”.

visit tronixlabs.com

Have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column, or join our forum – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in altronics, ISD2590, K9570, kit, kit review, silicon chip, tronixstuffComments (0)

Old Kit Review – Silicon Chip Transistor Beta Tester


After exploring a quiet , dusty electronics store in the depths of suburbia the other week, I came across this kit from Altronics (K2534) which is the subject of this review. The Transistor Beta tester is the second revision of a tester designed by John Clarke for the March 1991 issue of Silicon Chip magazine, and promises to offer a simple way of measuring the gain of almost any NPN or PNP bipolar transistor. But first some public answers to recent feedback…

John – Why do you publish these “Old Kit Reviews”?

They’re more of  a selfish article, like many electronics enthusiasts I’ve enjoyed kits for decades – and finding kits from days gone by is a treat. From various feedback some of you are enjoying them, so I’ll continue with them for fun and some nostalgia. If you’re not interested, just ignore the posts starting with “Old”!

Where’s the schematic?

After publishing a few kit reviews, people have been asking me for the schematics. For kits that are based on magazine articles from Silicon Chip and the like, the details are Copyright and I can’t legitimately give you a copy. You need to contact the magazine or kit supplier. The surviving electronics magazines often run “on the smell of an oily rag” so in order to support them I promote the idea of paying for copies which are obtainable from the magazine. Plus Australia is a small country, where people in this industry know each other through first or second connections – so I don’t want to annoy the wrong people. However Google is an awesome tool,  and if you want to make your own beta tester there are many example circuits to be found – so have fun.

Back to the review – what is “beta”?

Apart from a letter of the Greek alphabet and a totally-underrated form of VCR format, beta is a term used to define the amount of gain of a transistor. From the guide:

Silicon Chip transistor beta tester what is beta


Here’s our kit from 1991, rescued from the darkness of the store:

Silicon Chip transistor beta tester packaging

Which contained the nice box, plus all the required components except for an IC socket, and a few screws and mounting nuts that should have been included. The instructions looked to be a photocopy of a photocopy, harking back to the 1980s…

Silicon Chip transistor beta tester contents

Silicon Chip transistor beta tester components

Looks like an off-brand 555 has been used (or substituted), however a bit of research indicated that it is most likely from LG Semiconductor:

Silicon Chip transistor beta tester off brand 555

The PCB was made to the usual standard at the time, just drilled:

Silicon Chip transistor beta tester PCB rear

Silicon Chip transistor beta tester PCB front

The front panel was well done, and kindly pre-drilled by a previous customer. The kit came with a 3mm LED however this mystery person had drilled the hole out for a 5mm:

Silicon Chip transistor beta tester front panel

… but hadn’t cut the oblong for the slide switch wide enough. But the biggest problem was that the PCB was just a smidge too wide for the included enclosure:

Silicon Chip transistor beta tester PCB not fitting

Nevertheless it was time to get started, and the resistors were measured, lined up and fitted:

Silicon Chip transistor beta tester resistors lined up

Then the rest of the components fitted as normal, however they need to stay below the horizontal level of the slide switch bezel:

Silicon Chip transistor beta tester assembly 1

… which was somewhat successful. Then to fit the potentiometer, battery snap …

Silicon Chip transistor beta tester assembly 2

and the test leads:

Silicon Chip transistor beta tester assembly 3

 And we’re finished:

Silicon Chip transistor beta tester finished

How it works

Operation is quite simple, just wire up the test leads to the transistor’s base, collector and emitter – set the PNP/NPN switch and press test. Then you turn the knob until the LED just turns on – at which point the scale indicates the gain.

“Modern-day” replacements

Digital technology has taken over with this regard, and a device such as the one below can not only give the gain, but also the component details, identify legs, and much more:

Silicon Chip transistor beta tester modern tester gain

I’ll be sticking with this one for the time being. Jaycar have discontinued the analyser shown above, but Altronics have the “Peak” unit which looks even more useful.


Well… that was fun. A lot of promise, however with a few details not taken care of the kit was just a bit off. Considering this was around twenty years old and possibly shop-soiled I can’t complain. For the record the good people at Altronics have a great line of kits. Full-sized images and a lot more information about the kit are available on flickr.

And while you’re here – are you interested in Arduino? Check out my new book “Arduino Workshop” from No Starch Press.


In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in altronics, K2534, kit review, test equipment, tronixstuffComments (1)

Old Kit Review – Diesel Sound Simulator for Model Railroads


In this review of an older kit (circa 1993~1997) we examine the Diesel Sound Simulator for Model Railroads kit from (the now defunct) Dick Smith Electronics, based on the article published in the December 1992 issue of Silicon Chip magazine.

The purpose of this kit is to give you a small circuit which can fit in a HO scale (or larger) locomotive, or hidden underneath the layout – that can emulate the rumbling of a diesel-electric locomotive to increase the realism of a train. However the kit is designed for use with a PWM train controller (also devised by Silicon Chip!) so not for the simple direct-DC drive layouts.

K3030 diesel sound simulator kit


The diesel sound kit was from the time when DSE still cared about kits, so you received the sixteen page “Guide to Kit Construction” plus the kit instructions, nasty red disclaimer sheet, feedback card, plus all the required components and the obligatory coil of solder that was usually rubbish:

K3030 diesel sound simulator kit contents

Everything required to get going is included, except IC sockets. My theory is it’s cheaper to use your own sockets than source older CMOS/TTL later on if you want to reuse the ICs, so sockets are now mandatory here:

K3030 diesel sound simulator kit parts

The PCB is from the old school of “figure-it-out-yourself”, no fancy silk-screening here:

K3030 diesel sound simulator kit PCB

K3030 diesel sound simulator kit PCB bottom

Notice the five horizontal pads between the two ICs – these were for wire bridges in case you needed to break the PCB in two to fit inside your locomotive.

Actual assembly was straight-forward, all the components went in without any issues. Having two links under IC2 was a little annoying, however a short while later the PCB was finished and the speaker attached:

K3030 diesel sound simulator kit finished

How it works

As mentioned earlier this diesel sound kit was designed for use with the Silicon Chip train PWM controller, so the design is a little different than expected. It can handle a voltage of around 20 V, and the sound is determined by the speed of the locomotive.

The speed is determined by the back EMF measured from the motor – and (from the manual) this is the voltage produced by the motor which opposes the current flow through it and this voltage is directly proportional to speed.

Not having a 20V DC PWM supply laying about I knocked up an Arduino to PWM a 20V DC supply via an N-MOSFET module and experimented with the duty cycle to see what sort of noises could be possible. The output was affected somewhat by the supply voltage, however seemed a little higher in pitch than expected.

You can listen to the results in the following video:

I reckon the sound from around the twenty second mark isn’t a bad idle noise, however in general not that great. The results will ultimately be a function of a lower duty-cycle than I could create at the time and the values of R1 and R2 used in the kit.


Another kit review over. With some time spent experimenting you could generate the required diesel sounds, a Paxman-Valenta it isn’t… but it was a fun kit and I’m sure it was well-received at the time. To those who have been asking me privately, no I don’t have a secret line to some underground warehouse of old kits – just keep an eye out on ebay and they pop up now and again. Full-sized images and much more information about the kit are available on flickr.

And while you’re here – are you interested in Arduino? Check out my new book “Arduino Workshop” from No Starch Press.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in DSE, electronics, K3030, kit, kit review, model railway, tronixstuffComments (2)

Kit review – Altronics Logic Probe Mk II


Every month Australian electronics magazine Silicon Chip publishes a few projects, and in this kit review we’ll look at an older but still current example from August 2004 – the 3-state Logic Probe Kit (Mk II). This is an inexpensive piece of test equipment that’s useful when checking digital logic states and as a kit, great for beginners. Avid readers of my kit reviews may remember the SMD version we examined in June… well it wasn’t that much of a success due to the size of the parts. However this through-hole version has been quite successful, so keep reading to find out more


The kit is packaged in typical form, without any surprises:


 In typical Altronics fashion, an updated assembly guide is provided along with a general reference to common electronics topics:


 All the required parts are included – except for a 14-pin IC socket and two CR2016 batteries.


 The PCB makes soldering easy with the silk-screen and solder mask:


 However the resistor numbering is a bit out of whack, a few R-numbers are skipped. So before soldering, measure and line up all the resistors in numbered order – doing so will reduce the chance of fitting them in the wrong spot.


When it comes time to solder the power switch on the end, it’s necessary to clip off two tabs – one at each end of the switch. However this isn’t a problem:


Soldering in the rest of the components wasn’t any effort at all, they’ve been spaced around the PCB nicely:


 Once they’re in, it’s time to insert the pins that hold the probe (shown on the left below):


 A full-sized probe is included with the kit, which you cut down with a hacksaw to allow it to fit on the end of the PCB. Then solder a short wire from the tip’s collar and run it through the body as such:


 At this point, it’s time to break out the butane torch:


… with which you melt down the heatshrink over the tip, then fit it to the PCB and solder the probe wire:


At this point it’s wise to fit the batteries and test that the probe works, as the next stage is to heatshrink the entire circuit to the left of the LEDs:



Using the probe is incredibly simple – however note that it’s designed for working with 5V logic. If you need to use higher voltages the probe can be assembled with slightly different circuit to take care of that eventuality. Moving forward simply clip the lead to GND on the circuit under test, then probe where you want to measure. The LEDs will indicate either HIGH, LOW or the PULSE LED will light when a fault is apparent, or other need for further research into the circuit. Here’s a quick demonstration probing a signal from an Arduino board:


This through-hole version of the logic probe kit was much easier to construct than the SMD version, and worked first time. A logic probe itself is a very useful tool to have and I highly recommend this kit for the beginner who enjoys projects and is growing their stable of test equipment on a budget. You can find the kit at my store – Tronixlabs Australia.

Full-sized images available on flickr.  And if you made it this far – check out my book “Arduino Workshop” from No Starch Press.

Finally, check out tronixlabs.com.au – which along with being Australia’s #1 Adafruit distributor, also offers a growing range and great value for supported hobbyist electronics from Altronics, DFRobot, Freetronics, Jaycar, Pololu and much much more.

visit tronixlabs.com

As always, have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column, or join our forum – dedicated to the projects and related items on this website.

Posted in altronics, K2586, kit, kit review, logic probe, silicon chip, test equipment, tronixstuffComments (2)

Kit review – Altronics/Silicon Chip DC to DC Converter


Every month Australian electronics magazine Silicon Chip publishes a variety of projects, and in March 2004  they published the “DC-DC converter” project. Altronics picked it up and now offers a kit, the subject of our review. The main purpose of this converter kit is to allow replacement of expensive PP3 9V batteries with 2 AA cells, to enable a cheaper and longer lifespan over use. With a slight modification it can also act as a trickle-charger for 2 rechargeable AA cells (that can then supply power to the converter) via a plugpack. And there’s some educational value if you’re so inclined, as you can learn about voltage converters as well.


As usual for Altronics the kit is in a typical retail package:


…which includes the detailed instructions (based on the original Silicon Chip article), a handy reference guide and of course the parts:


The PCB has a good silk screen and solder mask:



and all the required parts are included:


It was nice to see plenty of extra black and red wire for modifications or final installations, the battery snap, 2 x AA cell holder and a DC socket for use with the optional plug pack mentioned earlier. That hand-wound inductor was interesting, and I couldn’t help but measure it on the LC meter:


It was supposed to be a 47 uH inductor, so let’s hope that doesn’t cause too much trouble. Assembly was quite straight-forward – just start with the smallest components first and build up. If you’re not going to have the trickle-charge function, heed the notes in the manual and don’t install D2 or R4. The only fiddly bit was the “short as possible” (red) link across the board:


And after a few more minutes it was finished. The external connections will vary depending on your application – however for the review I’ve got the 9V snap on the input, which makes it easy to connect the 2 AA cell holder to power the converter. Nice to see the holes around the perimeter of the board, which make mounting it more permanently quite easy.


After a bench clean-up it was time to connect 2 AA rechargeable cells and see what we can get out of the converter. The cells measured 2.77V together before connection, and without a load on the converter the resulting output was 8.825 V:


We can live with that. Furthermore the quiescent current (a situation with the power connected and not having a load on the output) was 2.5 mA. Thus it would be a good idea to have a power switch in a real-world environment. Speaking of the real world (!) how much current can you get out of the converter? Generally PP3 battery applications are low current, as the battery itself isn’t good for that much – even an expensive “Energizer Ultimate Lithium” offers only 800 mAh (for $16). So using higher-capacity rechargeable AA cells and this kit will save money.  A table is included with the instructions that shows the possible uses:


According to the table my 2.77V supply should be good for ~80 mA. With some resistors in parallel we made a dummy load of 69 mA and measured 0.37A current draw from the AA cells. Thus the key to this kit – you find a cheaper or more plentiful power supply at a lower voltage to save you the expense of providing the higher voltage.

For example, if you had a pair of Sanyo Eneloop rechargeable AA cells (total 2.4 V at 2 Ah) they would give you around 5.4 hours of life (ignoring the fall-off of voltage towards the end of their charge life – however the eneloops are pretty good in that regard). Whereas a disposable PP3 mentioned earlier would offer around 2.1 hours (at $16) or a rechargeable unit (which offers 8.4 V at 175 mAh) would only last around 25 minutes. Note that you can change two resistors in the circuit to alter the output voltage, and the values have been listed in the instructions for outputs up to 15 V.

Finally, let’s consider the output waveforms from the circuit. With the aforementioned load, here’s the output on the DSO:


… and for interest’s sake, the switching output from the TL499:




Apart from the described voltage-boosting functions this kit gives the interested builder experience with boost circuits and also the knowledge to create their own versions based on the original design, at a much lower cost than using other boost ICs . If you wanted a permanent certain voltage output, it would be better to breadboard the kit and experiment with the required resistors – then assemble the kit with the new values. And there is money and effort to be saved when subsituting with PP3 batteries. Finally, learning is a good thing!

So – a lot of fun and education for under $20. Purchase it from Altronics and their resellers, or read more about it in the September 2007 edition of Silicon Chip.

Full-sized images available on flickr. This kit was purchased without notifying the supplier.

And if you made it this far – check out my new book “Arduino Workshop” from No Starch Press.


In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in altronics, boost, converter, dc dc, K6330, kit review, learning electronics, silicon chip, tronixstuffComments (0)

Kit review – Altronics/SC PIC Logic Probe Kit


Every month Australian electronics magazine Silicon Chip publishes a few projects, and in this quick kit review we’ll look at an older but still current example from September 2007 – the 3-state PIC Logic Probe Kit. This is an inexpensive piece of test equipment that’s useful when checking digital logic states and as a kit, a challenging hand-soldering effort.


The kit is packaged in typical form, without any surprises:


As mentioned earlier this kit is an interesting challenge due to the size of the PCB and the use of surface-mount components. The designer’s goal was to have the entire unit fit inside a biro housing (without the ink!). Thus the entire thing is using SMT parts.

Thankfully the LEDs are packaged individually into labelled bags, as alone they’re identical to the naked eye. Although the kit wasn’t expensive, it would have been nice for one extra component of each type – beginners tend to lose the tiny parts. The cost could perhaps be offset by not including the usual solder which is too thick for use with the kit.


Nevertheless with some care assembly can begin. After cleaning the PCB with some aerosol cleaner, it was tacked it to the desk mat to make life a little easier:


If you want one of those rulers – click here. Before building the kit it occurred to me that the normal soldering iron tip would be too large, so I ordered a tiny 0.2mm conical tip for the Hakko:


The tip on your average iron may be too large, so take this into account when trying to hand solder SMT components. The instructions include a guide on SMT hand-soldering for the uninitiated, well worth reading before starting.

Moving forward, soldering the parts was a slow and patient process. (With hindsight one could use the reflow soldering method to take care of the SMT and then carefully fit the links to the PCB). The instructions are quite good and include a short “how to solder SMT” guide, a PCB layout plan:


… along with an guide that helps identity the components:


When soldering, make sure you have the time and patience not to rush the job. And don’t sneeze – after doing so I lost the PIC microcontroller for a few moments trying to find where it landed. Once the LEDs have been soldered in and their current-limiting resistors, it’s a good time to quickly test them by applying 5V and GND. I used the diode test feature of the multimeter which generates enough current to light them up.

Due to the PCB being single-sided (!) you also need to solder in some links. It’s best to do these before the button (and before soldering any other parts near the link holes), and run the wires beneath the top surface, for example:


… and after doing so, you’ll need more blu-tack to hold it down!


One of the trickiest parts of this kit was soldering the sewing needle at the end of the PCB to act as the probe tip – as you can see in the photo below, solder doesn’t take to them that well – however after a fair amount it does the job:


At this point it’s recommended you solder the wires to the PCB (for power) and then insert the probe into the pen casing. For the life of me I didn’t have a spare pen around here so instead we’re going to cover it in clear heatshrink. Thus leaving the final task as soldering the alligator clips to the power wires:



What is a logic probe anyway? It shows what the logic level is at the probed point in a circuit. To do this you connect the black and red alligator clips to 0V and a supply voltage up to 18V respectively – then poke the probe tip at the point where you’re curious about the voltage levels. If it’s at a “high” state (on, or “1” or whatever you want to call it) the red LED comes on.

If it’s “low” the green LED comes on. The third (orange) LED has two modes. It can either pulse every 50 mS when the logic state changes – or in “latch mode” it will come on and stay on when the mode changes, ideal for detecting infrequent changes in the logic state of the test point.

The kit uses a Microchip PIC12F20x microcontroller, and also includes the hardware schematic to make a basic RS232 PIC programmer and wiring instructions for reprogramming it if you want to change the code or operation of the probe.


The PIC Logic Probe is a useful piece of equipment if you want a very cheap way to monitor logic levels. It wasn’t the easiest kit to solder, and if Altronics revised it so the PCB was double-sided and changed the parts layout, there would be more space to solder some parts and thus make the whole thing a lot easier.

Nevertheless for under $17 it’s worth it. You can purchase it from Altronics and their resellers, or read more about it in the September 2007 edition of Silicon Chip. Full-sized images available on flickr. This kit was purchased without notifying the supplier. And if you made it this far – check out my new book “Arduino Workshop” from No Starch Press.


In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in altronics, K2587, kit review, logic probe, SMT, soldering, test equipment, tronixstuffComments (2)

Kit Review – SC/Jaycar USB Power Monitor


Every month Australian electronics magazine Silicon Chip publishes a variety of projects, and in December 2012 they published the USB Power Monitor by Nicholas Vinen. Jaycar picked it up and now offers a kit, the subject of our review. This small device plugs inline between a USB port and another device, and can display the current drawn, power and voltage at the USB port with a large LCD module. This is useful when you’re experimenting with USB-powered devices such as Arduino projects or curious how external USB devices can affect your notebook computer’s battery drain.


The kit arrives in typical Jaycar fashion:

… everything necessary is included with the kit:

The instructions arrive as an updated reprint of the original magazine article, plus the usual notes from Jaycar about warranty and their component ID sheet which is useful for beginners. The PCB is quite small, and designed to be around the same size as the LCD module:

As you can see below, most of the work is already done due to the almost exclusive use of SMD components:

That’s a good thing if you’re in a hurry (or not the best with surface-mount work). Therefore the small amount of work requires is simply to solder in the USB sockets, the button and the LCD:

It took less than ten minutes to solder together. However – take careful, careful note of the LCD. There isn’t a pin 1 indicator on the module – so instead hold the LCD up to the light and determine which side of the screen has the decimal points – and line it up matching the silk-screening on the PCB. Once finished you can add the clear heatshrink to protect the meter, but remember to cut a small window at the back if you want access to the ICSP pins for the PIC microcontroller:

How it works

The USB current is passed through a 50 mΩ shunt resistor, with the voltage drop being measured by an INA282 current shunt monitor IC. The signal from there is amplified by an op amp and then fed to the ADC of a PIC18F45K80 microcontroller, which does the calculations and drives the LCD. For complete details purchase the kit or a copy of the December 2012 edition of Silicon Chip.


First you need to calibrate the unit – when first used the meter defaults to calibration mode. You simply insert it into a USB port. then measure the USB DC voltage brought out to two pads on the meter. By pressing the button you can match the measured voltage against the display as shown below – then you’re done.

Then you simply plug it in between your USB device and the socket. Press the button to change the measurement. The meter can measure the following ranges:

For an operational example. consider the next three images are from charging my phone – with the power, current and voltage being shown:

“P” for power…

current in mA

“b” for bus voltage

If you want to use the USB ports on the right-hand side of your computer, just press the button while inserting the meter – and it flips around:

Finally – here’s a quick video of the meter at work, whilst copying a file to an external USB hard drive:


I really like this – it’s simple and it works. Kudos to Nicholas for his project. You can purchase it from Jaycar and their resellers, or read more about it in the December 2012 edition of Silicon Chip. Full-sized images available on flickr. This kit was purchased without notifying the supplier.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in jaycar, kc5516, kit review, monitor, power, silicon chip, USB

Welcome to “Silicon Chip” Magazine readers

Hello readers

Published in the January 2012 issue of “Silicon Chip” magazine is an eight page feature article by Jonathan Oxer introducing the Arduino system and how the hardware and software work together to allow anyone to turn their technological ideas into reality. If you have read Jon’s article and were directed here – thanks for visiting! We have much more content than just Arduino tutorials, however to get started with them please click here or select from one of the chapters listed in the “Arduino Tutorials” section on the right-hand side of this web page.  Our site is a work in progress and if you have any feedback or questions please email john at tronixstuff dot com, or visit our moderated Google Group.

For those not familiar with the magazine, here is the cover for the January 2012 issue:


So what is “Silicon Chip” magazine all about? It is Australia’s window to the wide world of electronics, backed by a team of engineers and enthusiasts with decades of experience and knowledge. Each month you can read about in-house projects by the team and also submitted by readers – covering basic circuits right through to digital and computer systems, quality hi-fi and audio projects, news, reviews, readers’ letters, the humorous columns and a wide variety of kits to assemble. There is also a wide range of advertising from related businesses that helps you find new products and suppliers that you may not have known about.

Silicon Chip is the only Australian electronics magazine and one of the few left in the world with a broad appeal to the beginner and expert alike, and the projects described are always good value and not priced or designed out of most peoples’ reach. I unashamedly recommend you pick up a copy from the newsagent or take out a subscription if possible, it’s a great read and there’s always lots to learn and laugh about.


Finally, that’s it for 2011. A big thank you to all of our readers for your visits, feedback, compliments, criticism, donations, and the crazy emails received through the year. And of course to all the great suppliers who help out with promotional considerations and sponsor our monthly competitions. Keeping this site together has been interesting, educational and a whole lot of fun, and I hope you think so too. There is a lot coming up for 2012 – so stay tuned via twitter, Google+, or subscribe by email or RSS on the right-hand side of this page.

Have fun and Happy New Year 🙂

John Boxall.

Posted in arduino, australia, magazine, silicon chipComments (2)

Kit review – High Accuracy LC Meter

Hello readers

Time for another kit review. Lately one of my goals has been to make life easier and in doing so having some decent test equipment. One challenge of meeting that goal is (naturally) keeping the cost of things down to a reasonable level. Unfortunately my eyesight is not the best so I cannot read small capacitor markings – which makes a capacitance meter necessary. Although I have that function within my multimeter, it is often required to read resistors in the same work session.

Thus the reason for this kit review – the High Precision LC Meter kit. The details were originally published in the May 2008 issue of Australia’s Silicon Chip magazine. The meter specifications are:

  • Capacitance – 0.1pF to over 800 nF with four-digit resolution;
  • Inductance – 10 nH to over 70 mH with four-digit resolution;
  • Accuracy of better than +/- 1% of the reading;
  • Automatic range selection, however only non-polarised capacitors can be measured.

The power drain is quite low,  between 8 (measurement) and 17 milliamps (calibration). Using a fresh 9V alkaline battery you should realise around fifty to sixty hours of continuous use. At this point some of you may be wondering if it is cheaper to purchase an LC meter or make your own. A quick search found the BK Precision 875B LCR meter with the same C range and a worse L range for over twice the price of the kit. Although we don’t have resistance measurement in our kit, if you are building this you already have a multimeter. So not bad value at all. And you can say you built it 🙂

Speaking of building, assembly time was just under two hours, and the kit itself is very well produced. The packaging was the typical retail bag:


The first thing that grabs your attention is the housing. It is a genuine, made in the US Hammond enclosure – and has all the required holes and LCD area punched out, so you don’t need to do any drilling at all:


The enclosure has nice non-slip rubberised edging (the grey area) and also allows for a 9V battery to be housed securely. The team at Altronics have done a great job in redesigning the kit for this enclosure, much more attractive than the magazine version. The PCB is solder-masked and silk-screened to fine standard:


There are two small boards to cut and file off from the main PCB. We will examine them later in the article. All required parts for completion were included, and it is good to see 1% resistors and an IC socket for the microcontroller:


At first I was a little disappointed to not have a backlit LCD module, however considering the meter is to be battery operated (however there is a DC socket for a plugpack) and you wouldn’t really be using this in the dark, a backlight wouldn’t be necessary. Construction was easy enough, the layout on the PCB is well labelled, and plenty of space between pins. Lately I have started using a lead-former, and can highly recommend the use of one:


Assembly was quite simple, just start with the lower profile components:



… then mount the LCD and the larger components:


… the switches and others – and we’re done:


The only problem at this point was the PCB holes for the selector switch, one hole was around 1mm from where it needed to be. Instead of drilling out the hole, it was easier to just bend up the legs of the switch and keep going:


At this stage one has to cut out two supports from the enclosure, which can be done easily. Then insert the PCB and solder to the sockets and power (9V battery snap). Initial testing was successful (after adjusting the LCD contrast…


If you look at the area of PCB between the battery and the left-hand screw there are eight pins – these are four pairs of inputs used to help calibrate and check operation of the meter. For example, by placing a jumper over a pair you can display the oscillator frequency at various stages:


Furthermore, those links can also be used to fine-tune the meter. For example one can increase or decrease the scaling factor and the settings are then stored in the EEPROM within the microcontroller. However my example seemed ok from the start, so it was time to seal up the enclosure and get testing. Starting with a ceramic capacitor, the lowest value in stock:


Spot-on. That was a good start, however trying to bend the leads to match the binding posts was somewhat inconvenient, so I cut up some leads and fitted crocodile clips on the end. The meter’s zero button allows you to reset the measurement back to zero after attaching the leads, so stray capacitance can be taken into account.

Next, time to check the measurement with something more accurate, a 1% tolerance silvered-mica 100 picofarad capacitor:


Again, the meter came through right on specification. My apologies to those looking for inductor tests – I don’t have any in stock to try out. If you are really curious I could be persuaded to order some in, however as the capacitance measurement has been successful I am confident the inductance measurement would also fall within the meter’s specifications.

As shown earlier, there were two smaller PCBs included:


The top PCB is a shorting bar used to help zero the inductance reading, and the lower PCB is used to help measure smaller capacitors and also SMD units. A nice finishing touch that adds value to the meter. The only optional extra to consider would be a set of short leads with clips or probes to make measurement physically easier.

When reading this kit review it may appear to be somewhat positive and not critical at all. However it really is a  good instrument, considering the accuracy, price, and enjoyment from doing it yourself. It was interesting, easy to build, and will be very useful now and in the future. So if you are in the market for an LC meter, and don’t mind some work – you should add this kit to your checklist for consideration. It is available from our store – Tronixlabs.com


visit tronixlabs.com

… which along with being Australia’s #1 Adafruit distributor, also offers a growing range and Australia’s best value for supported hobbyist electronics from DFRobot, Freetronics, Seeedstudio and much much more.

As always, have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column, or join our forum – dedicated to the projects and related items on this website.

Posted in K2533, kit review, LC meter, test equipment, tronixlabsComments (18)

Project – Simple RFID access system

In this tutorial you can make an RFID access system. It’s very simple and can be used with a wide variety of end-uses.

Updated 18/03/2013

The purpose of this project is to prototype a basic RFID access system. Although it is not that complicated, this article is my response to a kit reviewed in the Australian “Silicon Chip” (November 2010) electronics magazine. Their article describes the kit in detail – operation, schematic, use and installation. However the code for the microcontroller (PIC16F628A)  is not published due to the kit manufacturer holding copyright over the design.

This is a shame, as many organisations have been quite successful selling open-source kits. So instead of moaning about it, I have created my own design that matches the operation of the original, instead using the ATmega328 MCU with Arduino bootloader. Consider this a basic framework that you can modify for your own access system, or the start of something more involved.


There are pros and cons with the original vs. my version. The biggest pro is that you can buy the whole kit for around Au$40 including a nice PCB, solder it together, and it works. However if you want to do it yourself, you can modify it to no end, and have some fun learning and experimenting along the way. So let’s go!

The feature requirements are few. The system must be able to learn and remember up to eight RFID access tags/cards, etc – which must be able to be altered by a non-technical user. Upon reading a card, the system will activate a relay for a period of time (say 1 second) to allow operation of a door strike or electric lock. Finally, the RFID tag serial numbers are to be stored in an EEPROM in case of a power outage. When a tag is read, a matching LED (1~8) will show which tag was read. There are also two LEDs, called “Go” and “Stop” which show the activation status. The original kit has some more LEDs, which I have made superfluous by blinking existing LEDs.

This is a simple thing to make, and the transition from a solderless breadboard to strip board will be easy for those who decide to make a permanent example. But for now, you can follow with the prototype. First is the parts list:

  • Atmel ATmega328 with Arduino bootloader;
  • 16 MHz resonator (X1 in schematic);
  • ten LEDs of your choice;
  • two normally-open push buttons;
  • two 560 ohm resistors (all resistors 1/4 watt);
  • one 1k ohm resistor;
  • three 10k ohm resistors;
  • one BC548 transistor;
  • three 0.01 uF monolithic capacitors;
  • one 100 uF electrolytic capacitor;
  • one 1N4004 diode;
  • Microchip 24LC256 EEPROM;
  • 125 kHZ RFID module;
  • 125 kHz RFID tags/cards;
  • connecting wire;
  • large solderless breadboard;
  • LM7805 power regulator;
  • relay of your choice with 5V coil (example).

When selecting a relay, make sure it can handle the required load current and voltage – and that the coil current is less than 100mA.

If attempting to switch mains voltage/current – contact a licensed electrician. Your life is worth more than the money saved by not consulting an expert.

And here is the schematic (large version):


Here is the prototype on the solderless breadboard. For demonstration purposes an LED has been substituted for the transistor/relay section of the circuit, the power regulator circuitry has not been shown, and there are superfluous 4.7k resistors on the I2C bus. To program the software (Arduino sketch) the easiest way is by inserting the target IC into an Arduino-compatible board, or via a 5V FTDI cable and a basic circuit as described here.


The Arduino sketch is also quite simple. The main loop calls the procedure readTags() to process any RFID tag read attempts, and then monitors button A – if pressed, the function learnTags() is called to allow memorisation of new RFID tags. Each tag serial number consists of 14 decimal numbers, and these are stored in the EEPROM sequentially. That is, the first tag’s serial number occupies memory positions 0~13, the second tag’s serial number occupies memory position 14~28, and so on. Two functions are used to read and write tag serial numbers to the EEPROM – readEEPROMtag() and writeEEPROMtag().

The EEPROM is controlled via the I2C bus. For a tutorial about Arduino, I2C bus and the EEPROM please read this article. For a tutorial about Arduino and RFID, please read this article. The rest of the sketch is pretty self-explanatory. Just follow it along and you can see how it works. You can download the sketch from hereAnd finally, a quick video demonstration:

So there you have it. I hope you enjoyed reading about this small project and perhaps gained some use for it of your own or sparked some other ideas in your imagination that you can turn into reality.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in hardware hacking, learning electronics, microcontrollers, projects, RDM630, RDM6300, rfidComments (12)

Kit Review – Silicon Chip Low Capacitance Meter adaptor for DMMs

Hello readers

Time again for another kit review. In the spirit of promoting all things electronic and Australian, we’re going to look at a kit that was published in our electronics magazine Silicon Chip (March 2010) – their Low-capacitance meter adaptor for DMMs. Simply put, it converts capacitance (from a theoretical 1 picofarad) to millivolts, which you can then read with almost any digital multimeter. This is useful as even more expensive multimeters (such as my Fluke 233) only measure down to 1 nanofarad (1000 picofarads). Although this kit is available on the Australian market, the retailers will export to those abroad. If you are outside Australia and having trouble sourcing one, send me an email. Moving on…

Here is our unassuming finished product:


Please note that this is not an open-source product, so you need to either purchase the kit of parts, or a back-issue of Silicon Chip magazine, March 2010 for the schematic and instructions. Now it is time to get started. But before that, how does it work?

Without giving too much away, a very rough explanation would be that a square wave signal is formed, then cleaned up through a Schmitt trigger-inverter. This square wave is then split into two, one signal passing through the capacitor under test and some resistors, and the other signal passing through a calibration variable capacitor and the same value resistors – thereby both signals pass through two different RC circuits. Finally the two signals are fed through a XOR gate, which creates a series of positive pulses that are a function of the capacitor under test.

Kit assembly was not that difficult, like anything just take your time, read the instructions carefully, and don’t rush things. If you are happy with your through-hole soldering skills, and have a power drill, this kit will be easy for you to work with. Unusually for some kits, this one comes with almost everything you need:


The quality of the included housing is very good, there are metal threaded inserts for the screws; and even through the ICs are simple 74xx-series, sockets have been included. Resistors are metal film, the trimpots are enclosed multiturns – all very nice. I am a little disappointed with the housing/adhesive label combination however, in the past various kits from Jaycar would have a box with a nice silk-screened, hole-punched front panel. Such is life. The PCB is solder-masked and silk-screened, however a little less denser than PCBs from other kit suppliers:


And thus brings a slight issue with the housing and the PCB – either the PCB is too wide, or the box is too narrow. A quick clip of the PCB with some cutters will fix that:


The instructions are quite good – they are a reprint of the magazine article, and slightly modified by the kit production company. Furthermore, the silk-screening on the PCB makes things a breeze. The simple passives were easy to install, however take care not to overheat the variable capacitor, their casings can melt rather quickly:


Following that, the ICs were inserted, and the rotary switch. From experience, one should trim the shaft down to about a 25mm length before soldering it into the board. Take very good care when placing the rotary switch, there is a lump on the switch which matches the small circle at 8 o’clock on the PCB diagram. Finally, don’t forget to alter the switch so it only has four selections. Soldering it in can look difficult, but is not. Just push it into the PCB, checking it is flush, even and all the way in. Then bend a couple of the pins over, invert the PCB and solder away – as such:


Now it is time to start on the enclosure. Each end has two banana-type sockets, the left are the full binding-post, and the right are just sockets. Carefully mark where you want to start the holes – the positions are vertically half-way, and horizontally 15mm in from the edge, however double-check yourself. Always check the fit of the socket while drilling, as it is easy to go too far and make the holes too large – at which point you’ll have to buy another enclosure. Once you have the sockets fitted – on the left:


and on the right:


… you will need to solder the socket rear to the PCB pins (left) and a small link to the PCB pins (right). It is important to get a good, solid connection – as these sockets may come under a lot of use later on. Next it is time to start on the housing. If you can, photocopy the label so you have a drilling template:


You will notice in the above photo one of my favourite tools, a tapered reamer. Using that, you can carefully turn a small hole into a larger hole, without risking making a mess with a drill. Again, cut the rotary switch’s shaft before soldering:


And as punishment for using twitter at the same time, I had ended up drilling the back instead of the front. D’oh. However cosmetic appearance is secondary to functionality, so all is well. Next was to install the PP3 battery snap. The battery will be a tight fit, so a length of heatshrink has been supplied in order to avoid the battery case shorting with the PCB pin:


And finally we have finished soldering:


Now it is time for calibration. And for me to get a little cranky, which is quite rare as I am somewhat easygoing. Calibration requires three 1% tolerance capacitors, 100 pF, 1000 pF and 10000 pF. And they are not included with the kit. And can not be purchased from any of the kit retailers. So they had to be ordered from Farn… element-14 at a reasonable expense. Considering the kit production company also imports, wholesales and retails electronic components, they could have bought a volume of these special capacitors and added a few dollars to the price of the kit. Such is life. So here are the little buggers:


From top to bottom:

  • Silvered-mica 100 picofarad 1% tolerance, element-14 # 1264880, RS # 495745;
  • Polystyrene 1000 picofarad 1% tolerance, element-14 # 9520651, RS # 495868 (silvered mica) and
  • Polystyrene 10000 picofarad 1% tolerance, element-14 # 3358951, RS # 495953 (silvered mica)

However it is worth the effort to chase them down. There is no point using this kit if you calibrate with normal capacitors; their tolerance can be as much as 20 percent either way. Thankfully the calibration process is quite simple. You will need a small, plastic flat-blade screwdriver to make the adjustments, as your body has stray energy which can alter the capacitance measurements.

Before starting, connect your multimeter to the output sockets and set the range to millivolts – then adjust the variable capacitor until you have the meter display as close to zero as possible. This is used to ‘null out’ stray capacitance. Next, set the dial to A, connect the 100 pF capacitor to the input posts, and adjust VR3 until the meter displays one volt DC – this represents 100.0 picofarads:


I could not for the life of me get this to 1 volt. After fitting the case at the end, I tried again with the case on with the same result. It is very important to get the capacitor as close as possible to the binding posts, with such small values stray capacitance can affect the result. However in my line of work, one-tenth of a picofarad is not relevant. For now. Next, set the dial to B, connect the 1000 pF capacitor, and adjust VR2 until the meter displays 1 volt – this represents 1000 picofarads:


Excellent – spot on. Unfortunately the leads on my 10000 pF capacitor were not long enough to attach into the binding posts, so that step had to be passed. I will have to re-order the correct part next week and calibrate then. However the other two setting are basically working perfectly, which is a good indication for the general performance of the kit. Kudos to Jim Rowe from Silicon Chip magazine for this design. Before closing up the enclosure, I decided to wrap the battery with some paper, as having it  rub up against other parts is not a good idea:


Now for a test run – time to measure the smallest capacitors I have in stock, first a 4.7 picofarad ceramic:


and next, a 12 picofarad ceramic:


Excellent, we can call these readings a success. I was also quite amazed that the tolerance of the cheap ceramic capacitors was so low. Note that in real-life, you may not be able to have the capacitor under test directly connected to the binding posts. In these cases you will need a short set of heavy-gauge leads to the test capacitor. If you do this, you will need to adjust the variable capacitor to reset the display to account for stray capacitance in the leads.

In conclusion, this kit has proved very successful, with regards to assembly, the quality of components and instructions, and of course the final result. I made a few errrors with regards to the housing, but that didn’t affect the final result. And for less than fifty Australian dollars, I have a very low value capacitance meter. However in due course I would consider the purchase of a full LCR meter for greater accuracy and ease of frequent use (some can measure down to 0.1 picofarad). But for the time being, this has been an excellent, educational  and affordable solution. You can purchase the kit directly from Jaycar. High resolution images are available on flickr.

So have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column, or join our Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

[Note – The kit was purchased by myself personally and reviewed without notifying the manufacturer or retailer]

Posted in capacitance meter, jaycar, KC5493, kit review, learning electronicsComments (2)

Electronic components – the Diode

Hello readers

Although my posts have generally been about microcontrollers, kits and related items, I have been rather lax in writing about electronics in general, and that magical world of wonder known as analogue electronics… i.e “Before Arduino” 🙂 So let’s go back to some of the basics. Starting with the diode

What is a diode? It is an electronic component that allows current to only flow in one direction. Before the advent of semiconductors, vacuum tube diodes were used. Thankfully no more…

A diode is comprised of two types of semiconductor crystal (usually made from silicon or germanium) that are highly refined then doped with an impurity. Depending on the impurity, the crystal can either be called an “N-type” or “P-type”. When you put an N-doped region next to a P-doped region, a diode or PN junction is formed. In our diodes, the P-region is called the anode, and the N-region is called the cathode. As you can imagine, these properties are useful, allowing current to flow only in one direction.

The basic symbol for a diode in a circuit diagram or schematic is this:

So in a circuit, the current only flows in one direction, for example:

When a diode is connected in this way, it is said to be forward-biased, that is the anode is connected to a higher voltage than the cathode. If the diode was reversed, with the cathode connected to the higher voltage, it would not allow current to flow, and therefore would break the circuit. A forward-biased diode is considered to be a closed switch, as the voltage does not drop as the current passes through the diode. However that is assuming the diode is perfect. And like many other things in life, it is not perfect.

All diodes are not perfect, and have what is called a forward voltage drop, this is the amount by which the voltage decreases as the current passes through the diode from anode to cathode. For silicon diodes, this is ~0.7 volts; for germanium diodes ~0.3 volts.

Diodes are also manufactured to handle a certain amount of power. Recall that:

power (watts) = current (amps) x voltage (volts)

As the voltage drop with our normal diode is 0.7V, the power dissipated by the diode can be calculated by simply multiplying the current by 0.7.

For example, if we have a 1 watt diode, how much current can it handle?

1 = current x 0.7; current = 1/0.7

Current = 1.42

So the 1 watt diode can theoretically handle 1.42 amps of current.

What happens if you use a diode the other way, that is attempt to allow current to flow from the cathode through to the anode. Ideally nothing will happen – to a point. Diodes have a breakdown voltage, when a reverse-biased (backwards) diode starts to allow current to flow through it. The breakdown voltage of each type of diode is different, it depends on the manufacturer. The best way to find out what the breakdown voltage of your diode is to check the data sheet. For example, a popular diode is the 1N4001. From page two of the data sheet (pdf), comes the following table:


So for the 1N4001 diode, the breakdown voltage is 50V. Peak repetitive means that the diode can sustain doing this more than once. Excessive voltage will not usually destroy a diode. Excessive current will destroy a diode. This is interesting, as you can use a diode as a voltage regulator, provided that you don’t exceed the maximum current it can handle. Refresh your memory about voltage division with resistors. The disadvantage of using two resistors is that it can be difficult to purchase precise values.

So let’s use a zener diode instead. They are manufactured with a much more precise (and lower) voltage; and handle less power. Zener diodes have a slightly different symbol:

Zener diodes will usually (hopefully) have their breakdown voltage within their part number. For example, an NXP 4.7V zener diode’s part number is: BZX79-B4V7. The 4V7 is the breakdown voltage, with a V for the decimal point. It can handle 500 mW, but this is not obvious – once again, you will need the data sheet (pdf). Below is a photo of a typical zener diode. It is very small, the grid paper beneath it is 5mm square. The ring or dark band around one end of the diode always indicates the cathode end:


And now for an example. We have a tiny Zilog ePIR that requires a nice smooth 3.3v DC, and only draws 10mA, however the power rail on our prototype is 5V. This is a job for a 3.3V zener diode. Here is our schematic:


We need to calculate the appropriate resistance to limit the current through our zener diode. We are using a Fairchild BZX55C3v3 (data sheet pdf). Maximum power is 500mW or 1 watt. To calculate the value of the resistor, we will need the maximum current for the diode, calculated by

current = power / voltage

current = 0.5 watts / 3.3 volts

current = 0.150 A or 150 mA.

Using Ohm’s law, resistance = voltage /current

resistance = 1.7 volts / .15 A

resistance = 11.333333 = 12 ohms

So we would use a nice metal film 1% tolerance 12 ohm resistor, rated at 500 mW. Easy, 1.2 cents from RS or element-14.

Another type of diode is the signal diode. They handle much less current, usually around 100 mA, but are more suited for high-frequency signals, or semiconductor protection.Signal diodes can have a high breakdown voltage, but low power handling ability. A very popular signal diode used is the 1N4148 (data sheet), an example of which is below:


For example, a signal diode may be places across the coil of a relay that is being controlled by a transistor – as it allows the current produced by the change in magnetic field when the coil is deactivated to head through the coil instead of the transistor. For example, when using an Arduino to control a relay coil:



Our next diode type is the germanium diode. They have a very small voltage drop of 0.2V, and are mostly used in crystal radio sets. They are very fragile, but are ideal for putting across a radio wave signal to convert it from AC to DC, which can then be amplified. If you are interested, here are some guides to making a crystal radio.

Another type of diode is the Schottky diode (named after the German physicist Walter Schottky). The symbol for a schottky diode is this:

There are two main differences between a schottky diode and a normal diode. One – a schottky diode does not have a discernible recovery time between conducting and not conducting a current. For example, a normal diode may take around a few hundred nanoseconds; whereas a schottky does not. This makes them useful in situations that involve very very high speed switching of current (for example, DC-DC converters such as Limor Fried’s mintyboost). Two – a schottky diode has a smaller forward voltage, a typical example (data sheet) is 0.55v.

Finally we come to rectifier diodes. Their main feature is the ability to handle large amounts of current, from 1 amp upwards; and higher breakdown voltages. For example the 1N4001 (data sheet) diode is 50V at 1 amp; the 1N5401 (data sheet) is 100V at 3 amps. The main purpose of these diodes is to protect against incorrect polarity from power supplies, and to convert AC to DC. For example, if you were designing a childrens’ toy that used a 9V battery, you would use reverse-bias a rectifier diode between 9V and GND in case the child forced the battery in the wrong way.

But how can rectifier diodes convert AC to DC power? Very easily – through the use of a bridge rectifier. A bridge rectifier is basically four rectifier diodes connected together, for example:




When the AC power is between 0 and maximum wave, the positive DC rail is fed by the path: 1,2,3,4; the negative DC rail is 8,7,6,5. When the AC power is between 0 and minimum wave, the positive DC rail is fed by the path: 5,6,3,4; the negative DC rail is: 8,7,2,1.

Bridge rectifiers come in various shapes and sizes, for example DIP packaging for 1A 100V models:

right through to 300A 1600V models…

Last but not least is the light emitting diode (LED). An LED is a special kind of diode, when it is forward-biased and a current applied, it releases energy in the form of light instead of heat. Here is the common schematic symbol for an LED:

When using an LED it is critical to ensure you have the correct voltage, otherwise your LED will overheat, burn your fingers when you touch it then eventually break. Always consult your data sheet. Calculating the correct voltage is quite simple. Using a bog-standard 5mm RED LED as an example (data sheet), you can use the following formula:

R = (Vs-Vled) / A


  • R = value of resistor to use in ohms
  • Vs is your supply voltage in volts DS
  • Vled is the forward voltage of the LED at the recommended current
  • A is the recommended operation current of the LED

So for our example, we will use a 9V battery, and the LED from the data sheet above, Vled is 2V and A is 20 mA or 0.02 A

That gives us R = (9-2)/0.02 = 7/0.02 = 350 ohms.

Therefore, place a 350 ohm resistor between the positive of the battery and the anode of the LED. The most popular value of resistor to use would be a 390 ohm, 1/4 watt.

You can find LEDs in many different colours, and also units with two or more LEDs in the one housing, example red, green and blue. Some LEDs also create light in non-visible wavelengths, such as infra-red – these are used in remote-control applications and night-vision equipment. However if you are reading this, you would know by now where to find LEDs.

Well that wraps up my introduction to diodes. And if you made it this far – check out my new book “Arduino Workshop” from No Starch Press.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.



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