Tag Archive | "meter"

Clock Kit Round-up – December 2011

Hello Readers

If there’s one thing that I really like it’s a good clock kit. Once constructed, they can be many things, including:

  • a point of differentiation from other items in the room;
  • a reminder of the past (nixie tubes!) or possible visions of the future;
  • the base of something to really annoy other people;
  • a constant reminder to get back to work;
  • a source of satisfaction from having made something yourself!

So just for fun I have attempted to find and list as many interesting and ‘out of the ordinary’ kits as possible, and ignored the simple or relatively mundane kits out there. If you are in the clock kit business and want a mention, let me know. So in no particular order, we have:

adafruit industries “ice tube” clock

Based around a vintage Soviet-era vacuum IV-18 type fluorescent display, the ice tube clock is a rare kit that includes a nice enclosure which keeps you safe from the high voltages as well as allowing the curious to observe your soldering skills. I reviewed this kit almost a year ago and the clock is still working perfectly. Here is a video of the ice tube clock in action:

After some travelling meeting various people it seems that quite a few of us have an ice tube clock. There is something quite mesmerising about the display, perhaps helping to recall memories of our youth in the 1970s and 80s.

nootropic design Defusable Clock Kit

As recently reviewed, this kit allows you to build a simulated ‘countdown’ timer for a hypothetical explosive device that also doubles as a clock with an alarm. For example:

Whatever you do, don’t make a ‘fake bomb’ and leave it out in public! Only bad things could happen 🙂

ogilumen nixie tube kits

Not a clock kit as such, however they have made doing it yourself very easy with their power supply and IN-12A nixie board kits. We made one ourselves in a previous review, as shown below:

Alan Parekh’s Multimeter Clock Kit

This is certainly one from left field – using the analogue multimeters to display hours, minutes and seconds. See Alan describe his kit in this video:

Certainly something different and would look great on the wall of any electronics-themed area or would easily annoy those who dislike the status-quo of clock design.

akafugu VFD Modular Clock

The team at akafugu have created a modular baseboard/shield kit which holds a shield containing four IV-17 alphanumeric nixie tubes to create your own clock or display system:

vfd-7

Unlike some of the other nixie tube kits the firmware has been made public and can be modified at will. In the future different display shields will be available to extend the use of the kit.

tubeclock.com kits

This site has two kits available, one using either four or six Soviet-era IN-12 type nixie tubes:

large_red

… and another kit using the Soviet-era IN-14 nixie tubes:

You have to hand it to the former Soviet Union – they knew how to over-produce nixie tubes. One rare example where we can benefit from a command economy!

evil mad science clocks

The certainly not evil people have two clock kits, the first being the Bulbdial Clock Kit:

This uses a unique ring of LEDs around the circumference of the clock face to create shadows to mark the time. It is also available in a range of housing and face styles. Their other kit of interest is the Alpha Clock Five:

The photo of this clock doesn’t do it justice – the alphanumeric displays are 2.3″ tall, making this one huge clock. It also makes use of a Chronodot real-time clock board, which contains a temperature-controlled oscillator  which helps give it an accuracy of +-/ 2 minutes per year. Furthermore you can modify this easily using an FTDI cable and the Arduino IDE with some extra software. Would be great for model railways (or even a real railway station) or those insanely conscious about the time.

Kabtronics Clock Kits

This organisation has several clock kits which span a range of technology from the later part of the twentieth century. These guys can only be true clock enthusiasts! Starting with the 1950s, they have their Nixie-Transistor Clock:

neononwall

Look – no integrated circuits, leaving the kit true to the era. If you need to hide from someone for a weekend, building this would be a good start. Next we move onto the 1960s and the Transistor Clock:

onwall_l

The 1960s brought with it LEDs so they are now used in this kit, however the logic is still all analogue electronics. However next we can move to the 1970s, and finally save some board space with the TTL Clock:

ttlclock_1721

This would still be fun to assemble but somewhat less punishing for those who don’t enjoy solder fumes that much. However you still have a nice kit and something to be proud of. Finally, the last in the line is the 1980s-themed Surface-Mount Technology Clock:

smtclock_l

So here we have a microcontroller, SMT components, and a typical reduction in board size. Their range is an excellent way of demonstrating the advances in technology over the years.

The GPS FLW Display Clock

Wow – this clock makes use of huge Burroughs B7971 15-segment nixie tube displays and a GPS receiver to make a huge, old-style/new-tech clock. Check out the demonstration video:

This thing is amazing. And it is actually cheaper to buy a fully-assembled version (huh). The same organisation also offers another GPS-controlled clock using IN-18 nixie tubes:

nixichron10

Again, it isn’t inexpensive – however the true nixie tube enthusiasts will love it. This clock would look great next to a post-modern vintage hifi tube amplifier. Moving forward to something completely different now, we have the:

adafruit industries monochron®

Almost the polar opposite of the nixie-tube clocks, the monochron uses an ATmega328 microcontroller and a 128 x 64 LCD module to create some interesting clock effects. For example:

Many people have created a variety of displays, including space invaders and the pong game simulation. The clock also includes the laser-cut acrylic housing which provides a useful and solid base for the clock.

Spikenzie Labs Solder : Time™ watch kit

Technically this is a watch kit, however I don’t think that many people would want to walk around wearing one – but it could be used in more permanent or fixed locations. Correct me if I’m wrong people. However in its defence it is a very well designed kit that is easy to solder and produces a nice clock:

It uses a separate real-time controller IC to stay accurate, and the design However this would be a great suggestion as a gift for a younger person to help them become interesting in electronics and other related topics. The asm firmware is also available for you to modify using Microchip MPLAB software if that takes your fancy.

Velleman Kits

The Velleman company has a range of somewhat uninspiring clock kits, starting with the Scrolling/Rolling LED Clock:

… the 2ÂĽ” 7-Segment Digital Clock:

This clock includes the housing and also accepts an optional temperature sensor, and therefore can display this as well. There is also the aptly-named – Digital LED Clock:

mk151

It tells the time and would be useful in a 1980s-era idea of the future movie set. The final velleman clock kit is the Jumbo Single-Digit Clock:

In all fairness this one looks quite interesting – the LED display is 57mm tall and the time is display one digit at a time. It is powered by a PIC16F630 however the firmware is proprietary to velleman.

Nocrotec Nixie Clocks

This company has a range of kits using nixie tubes and numitrons (low voltage incadescent displays in tubes). One particularly lovely kit is their IN-8 Blue Dream kit:

in-8-bd-h-side-blue

The blue glow at the base of the nixie tubes is due to an LED mounted at the bottom of the tube. Another aesthetically-pleasing kit is their Little Blue Something nixie clock. Check out their demonstration video:

nixiekits.eu

More IN-12 nixie clocks from Germany, the first being the Manuela_HR. You can buy the kit without an enclosure, or choose from the ‘office’ style:

… or this funky number:

You can specify it with RGB LEDs which colour-cycle to provide the effect shown above. For those not too keen you can also buy the kits pre-assembled. Their other kit is the Sven:

Sven_IN-8-2_720

It is available with IN-8 or IN-14 nixie tubes. The design quality of the enclosure is outstanding, a lot of effort has been made to produce a complete kit that “won’t look like a kit” when completed.

Minty Time

This is a small binary clock kit that fits in an Altoids tin:

This is a nice little kit as it is inexpensive, easy to make and very well documented. You could also mount this in a variety of flat surfaces, limited only by your imagination.

The Chronulator

Here we find a unique design that uses analogue panel meters in a similar method to the multimeter clock detailed previously. Here is an example of the completed kit:

IMG_1113

The kit contains the electronics and meters (or you can delete the meters for a discount if you already have some) however the housing is up to you. Furthermore, this kit has some of the best instructions (.pdf) I have ever seen. They are a credit to the organisation. Our final clock kit is the …

Denkimono

This is another clock kit in the style of ‘suspicious bomb timer’-looking – and it pulls this off quite well. Consider the following video demonstration:

As well as a normal clock it can function as an alarm, stopwatch, countdown timer and lap counter. The instructions (.pdf) are well written and easy to follow. Furthermore the Denkimono is also well priced for the kit and delivery.

Hopefully this catalogue of clock kits was of interest to you. If you have found some other kits to add to the list, or wish to disagree or generally comment about this article please do so via the comment section below. This article was not sponsored in any way.

Have fun and keep checking into tronixstuff.com. Why not follow things on twitter, Google+, 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.

Posted in clocks, kit review, nixie, review, TTL, VFDComments (8)

Review – Tenma 72-7222 Digital Clamp Multimeter

Hello readers

The purpose of this article is to examine the Tenma 72-7222 Digital Clamp Multimeter supplied for review by element-14/Farnell/Newark. The Tenma is a strongly featured yet inexpensive piece of test equipment – and considerably good value when you consider there is a current clamp for measuring high AC currents. So let’s have a look and see what we have.

Initial Impression

The Tenma arrives in a retail box, and generally nicely packaged. Naturally this has nothing to do with the performance of the meter at all, but at least they made an effort:

Opening up we find a nicely rounded group of items: the meter itself, some no-name AAA cells, test leads, a thermocouple for temperature measurement, a surprisingly articulate and well-written user manual, and the unit itself – all within a nice pouch. Wow – a pouch. Agilent? Fluke? All that money for a DMM and you don’t include a pouch?

Recent test equipment reviewers have made pulling apart the unit part of the review – so here goes… the back comes off easily:

No user-replaceable fuses… instead a PTC. A closer look at the PCB:

A very neat and organised PCB layout. There are plastic tabs that hold the PCB in along with a screw, however the case flexed too much for me to warrant removing the PCB completely. The spring for the clamp meter is locked in nicely and very strong, it won’t give up for a long time. Pulling the clamp base out reveals the rest of the PCB:

Installation of the battery is two stage procedure, first you need to remove a screw and then slide out the rear door:

… then insert the AAA cells into a frame, which is then inserted inside the unit:

The physical feel of the unit is relative to the purchase price, the plastic is simple and could be quite brittle if the unit was dropped from a height. The user manual claims the unit can be dropped from up to a height of one metre. Onto carpet? Yes. Concrete? Perhaps not. However like all test equipment one would hope the user would take care of it whenever possible. The clamp meter is very strong due to the large spring inside the handle, which can be opened up to around 28mm. The included leads are just on one meter long including the length of the probe:

The leads are rated to Category I 1000V (overkill – the meter can’t go that high) and 600 V Category II – “This category refers to local-level electrical distribution, such as that provided by a standard wall outlet or plug in loads (for example, 115 AC voltage for U.S. or 200 AC voltage for Europe). Examples of Measurement Category II are measurements performed on household appliances, portable tools, and similar modules” – definition from from National Instruments.  Unlike discount DMMs from unknown suppliers you can trust the rating to be true – otherwise element-14 wouldn’t be selling it.

Unit Specifications

  • Voltage Measuring Range DC:200mV, 2V, 20V, 200V, 600V
  • Voltage Measuring Range AC:2V, 20V, 200V, 600V
  • Current Measuring Range AC:2A, 20A, 200A, 400A
  • Resistance Measuring Range:200ohm, 2kohm, 20kohm, 200kohm, 2Mohm, 20Mohm
  • Temperature Measuring Range:-40°C to +1000°C
  • DMM Response Type:True RMS
  • DMM Functions:AC Current, AC/DC Voltage, Resistance, Temperature
  • Ranging:Auto
  • Display Count:1999
  • AC Current Range Accuracy:± (1.5% + 5d)
  • AC Voltage Range Accuracy:± (1.2% + 5d)
  • Accuracy:± (1.0% + 3d)
  • Current AC Max:400A
  • Current Range AC:2A, 20A, 200A, 400A
  • DC Voltage Range Accuracy1:± (0.8% + 1d)
  • Resistance Range Accuracy:± (1.0% + 2d)
  • Temperature Measuring Range:-40°C to +1000°C

The only measurement missed out on is DC current, however there is the Tenma 72-7224 which has DC current and frequency ranges. Finally, all the modes and buttons can be selected while holding the meter with one hand – for both left- and right-handed folk.

Measurement experience

Normally I would compare the measurements against my Agilent U1272A, however it’s out to lunch. Instead, a Fluke 233. First, AC voltage from the mains:

Next, a few DC voltage measurements:

Now for some resistance measurements. Higher values near the maximum of 20M Ohm can take around four seconds to measure:

Forward voltage of a 1N4004 diode:

dfv (1)

Now off to the kitchen for some more measurements – first with the thermocouple:

The boiling water test – 100 degrees Celsius (you can also select Fahrenheit if so inclined):

And now to test out the AC current clamp meter function with a 10A kettle at boiling point. First, using the 20A current range:

And then again on the 400A current range:

As always, it’s best to use the multimeter range that more closely corresponds with the current under test. The meter also has a continuity test with a beeper, however it was somewhat slow and would often take around one second to register – so nothing too impressive on that front. The meter can record the maximum value with the grey button, or hold a reading using the yellow button.

Conclusion

The Tenma 72-7222 works as advertised, and as expected. It is a solid little unit that if looked after should last a few years at a minimum. It certainly has a few limitations, such as the 1999 count display, lack of backlight, and the average continuity function. But don’t let that put you off. For the price – under Au$30 – it is a certified deal. If you need a clamp current meter for odd jobs or a casual-use multimeter and you are on a limited budget, the Tenma will certainly prove a worthwhile purchase. Full-size images are available on Flickr.

You can purchase a Tenma 72-7222 from element-14, Farnell and Newark.

Thanks for reading! Have fun and keep checking into tronixstuff.com. Why not follow things on twitter, Google+, 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 Tenma 72-7222 Digital Clamp Multimeter was a promotional consideration from element-14/Farnell/Newark]

Posted in 72-7222, clamp meter, element14, multimeter, review, tenma, test equipmentComments (4)

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:

retailkitss

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:

hammondcasess

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:

pcbss2

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:

partsss1

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:

leadformerss

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

assemble1ss

 

… then mount the LCD and the larger components:

assemble2ss

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

finishedsolderingss

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:

switchlegsss

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…

inittestss

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:

calibrationss

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:

3p9pfss

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:

99pfss

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:

pcbadaptorsss

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 twitter, Google+, 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)

Kit review – Current Clamp Meter Adaptor

Hello readers

Time for another kit review. Over the last few days I have been enjoying assembling a useful piece of test-equipment – a Current Clamp Meter adaptor. This kit was originally described in the September 2003 issue of Silicon Chip magazine. The purpose of this adaptor is to allow the measurement of AC current up to around 600 amps and DC current up to 900 amps. A clamp meter is a safe method of measuring such high currents (which can end you life very quickly) as they do not require a direct connection to the wire in question. As you would realise even a more expensive type of multimeter can only safely measure around ten amps of current, so a clamp meter becomes necessary.

To purchase a clamp meter can be expensive, starting from around $150. Therein lies the reason for this kit – under $30 and a few hours of time, as well as a multimeter that can measure millivolts DC/AC.

How the adaptor works is quite simple. It uses a hall-effect sensor to measure magenetic flux which is generated by the current flowing through the wire being measured. The sensor returns a voltage which is proportional to the amount of magnetic flux. This voltage is processed via an op-amp into something that can be measured using the millivolts AC/DC range of a multimeter. As the copyright for the kit is held by Silicon Chip magazine, I cannot give too much away about the design.

You can purchase a complete kit from Tronixlabs, or build one yourself by following the article in the magazine.  The hall effect sensor UGN3503 is now out of production, but according to the data sheet (.pdf), the Allegro A1302 is a drop-in replacement.

Now, time to get started. To make life easier I forked out for the whole kit, which arrived as below:

bagofpartsss

Upon opening the bag up, one is presented with the following parts:

parts1ss

parts2ss

It is great to see everything required included with a kit. And the extra battery-clamp is a nice bonus. As usual an IC socket was not included, however these can be had for less than five cents each… so I have recently solved that problem by importing a few hundred myself. The hall effect sensor is very small; considering the graph paper below is 5mm square:

hallsensorss

The PCB was very well done – to a degree. The solder-mask and silk-screening was up to standard:

pcbss

… however a few holes needed some adjustment. Doing a component test-fit before soldering really paid off, as none of the holes for the PCB pins were large enough to accept the pins, and one of the sensor socket holes needed some modification:

holedrillss

A small hand-held drill is always a handy thing to have around. Once those errors were taken care of, actually soldering the components to the PCB was simple and took less than ten minutes. The potentiometer VR3 needed to be elevated by 3.5mm so it would fit through the enclosure panel in line with the power switch. As I couldn’t use PCB pins, a few link offcuts from the resistors worked just as well. When soldering the components, start with the low-profile items such as resistors, and finish with the switch and potentiometer:

pcbsolderedss

Now it was time to make the clamp. First up was to cut the iron-powdered toroidal core in half. All I had to do this with was a small hacksaw, so I hacked away at it for about half an hour. This process will make a mess, filings will go everywhere. So you will need some pointless rubbish to catch the filings with:

rubbishss

Each half of the core is placed inside the clamp. Until I am completely happy with the clamp they will be held in with blutac. A lead also needs to be constructed, with the sensor at one end and the 3.5mm stereo plug at the other. Some heatshrink is provided to cover the ribbon cable, but I recommend placing some over the solder joints where the sensor meets the ribbon cable, as such:

clampleadss

Next, the sensor needs to be placed between the two halves of the core – however a piece of plastic slightly thicker needs to sit next to the sensor, to stop the clamp damaging the sensor by closing down on it. Then, using the continuity function of a multimeter, check that there aren’t any shorts in the lead. Feed the newly-constructed lead through the battery clamp in order to keep things relatively neat and tidy, and you should result with something like this:

clampdoness

As you can see I have had a few attempts at cutting the core. The next step was to drill the holes for the enclosure, and then solder the wires that run from the PCB, run them through the hole in the side of the enclosure, and fasten the banana plugs to plug into the multimeter.

Now it was time to start calibration. There are two stages to this, and both are explained well in the instructions. This involves adjusting the trimpots which control the output voltage in millivolts, which can be affected by charge in the human body. Therefore it is recommended to use a plastic screwdriver/trimming tool to make the adjustments:

plasticsdriver

They are generally available in a set or pack for a reasonable price. The second stage of calibration involves creating a dummy DC current load using a 12v power supply, 5 metres of enamelled copper wire and a 18 ohm 5 watt resistor:

clampdoness

By putting 100 turns of the copper wire around one side of the clamp, putting the resistor in series and looping it into 12 volts, the current drawn will be 0.667 amps. (Ohm’s law – voltage/resistance = current). Then it is a simple task to set the multimeter to millivolts DC and adjust potentiometer VR1 until it displays 66.7 mA:

calibratedss

So there you have it – 66.7 millivolts on the multimeter represents 660 milliamps of current. So 1 amp of current will be 100 millivolts on your multimeter. Excellent – it works! The whole mess was inserted into the enclosure, and I was left with something that looked not terribly unprofessional (time to invest in a label-maker):

finishedss

It turns out that the thick OFC cable and the battery wouldn’t be able to coexist in the enclosure, so the battery is external.

The current clamp meter kit was an interesting and satisfying kit to assemble. Originally I assumed it would be simple, but it required plenty of drilling, cutting the darn toroid in half, tricky soldering for the clamp lead, and some patience with lining up the holes for the enclosure. Not a kit for the raw beginner, but ideal for teaching with a beginner to improve their assembly skills, or anyone with some experience. Plus it really does work, so money has been saved by not having to buy a clamp meter or adaptor.

You can order your own kit directly from our store at tronixlabs.com. High resolution images are available on flickr.

Finally, check out tronixlabs.com – 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, Seeedstudio and much much more.

visit tronixlabs.com

As always, have fun and keep checking into tronixstuff.com. Why not follow things on twitter, Google+, 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, current clamp meter, K2582, kit review, learning electronics, test equipment, tronixlabsComments (4)

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:

finishedss5

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:

partsss3

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:

pcbss1

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:

filedpcbss

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:

resiscapsss

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:

solderrotaryss

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:

left-endss

and on the right:

right-endss

… 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:

labelsss

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:

drilledboxss

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:

pp3snapss

And finally we have finished soldering:

donesolderingss

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:

calibrationcapsss

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:

cal1ss

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:

cal2ss

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:

battpaperss

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

4p7ss

and next, a 12 picofarad ceramic:

12p0ss

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 twitter, Google+, 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)


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