Tag Archive | "ICL7660"

bbboost chapter five – the power supply module

[3 July 2010 – this project has been retired, but the posts left for reference]

Greeting again to followers of the bbboost journey. It has been a month since the last instalment, however the 20V DC plug pack took a long time to arrive from the land of China. Nevertheless, the project is moving forward. For my new readers, the bbboost is a power supply that can be assembled by a beginner, and can offer a smooth variable DC output voltage of between ~1.8 and ~20 volts – perfect for experimenting, breadboard, and generally saving money by not buying batteries. You can just make a PCB version, or mount it in an enclosure like a professional desktop unit. No mains voltage wiring is required, so it will fine for the younger enthusiasts. Follow the project from here.

This time I have breadboarded the power supply module, using the circuit described in chapter two.  Let’s have a bit of a look:

power-layout

power-layout2

These trimpots were ok, but it would be preferable to use the fully enclosed dustproof versions. Will order some and try ’em out.

trimpots

One trimpot (the blue and white one) is 5k ohm, – to adjust between the full range, so this is the ‘coarse’ adjuster; the other trimpot is only 500 ohms and changes the voltage selected by the coarse pot by around +/- 1.2 volts. The purpose of having two controls is to make it very easy to select your required voltage down to one-hundredth of a volt. The following video clip is a rough example of this type of adjustment in action:

This power supply will also be designed for installation into a nice enclosure, so in that case one would use normal-sized potentiometers for the coarse and fine voltage adjustment.

Posted in bbboost, projects, test equipmentComments (0)

Part Review – Intersil ICL7660

Hello readers

Today we are going to quickly examine a very simple yet useful part – the Intersil ICL7660 CMOS voltage converter. Huh? This is the part you have been looking for when you needed -5V and you’re not running off a multi-tap transformer. For example, some old-school TTL electronics projects need +/-5VDC power rails. Or if you are using the ICL7107 analogue to digital/3.5-digit display driver IC (as used in my defunct bbboost project).

But first of all, let’s say hello:

icl7660small

To do so with the ICl7660 is very simple, you only need two 10uF electrolytic capacitors! Honestly, I couldn’t believe my luck when I discovered this part, that is why I am writing about it today.

Firstly, how does it work? A very simple definition would be: the 7660 charges one capacitor, then the other – an oscillator controls the charging cycles between C1 and C2 and inverts the polarity, allowing the capacitors to discharge at an inverted voltage (negative instead of positive). For a more detailed explanation, have a loot at the data sheet. Furthermore, if the oscillation frequency interferes with other parts of your circuit, you can boost the oscillation rate with the use of a NAND gate, from an external logic IC (4011, etc.)

However due to the oscillations, there is a ripple in the supplied -5V. I only wish I had an oscilloscope to show you this, perhaps next month. In the meanwhile, there is an explanation of this in the data sheet.

At this stage, let’s have a quick look at an example circuit, from the data sheet – figure 13A.

7660circuit

And here it is in real life. The circuit on the breadboard to the left is my simple 12VAC > 5VDC converter. I am not that well off at the moment, so it will have to do.

7660circuitrealsmall

So there you have it  – a very easy and cheap way to get yourself -5 volts DC. Some information from this review obtained from Intersil website and the ICL7660 data sheet; these parts purchased by myself without knowledge of manufacturers or retailers.

Once again,  thank you for reading. Please leave feedback and constructive criticism or comments at your leisure… and to keep track, subscribe using the services at the top right of this page!

Posted in ICL7660, lesson, part review, tutorialComments (2)

bbboost chapter three – the digital voltmeter

[3 July 2010 – this project has been retired, but the posts left for reference]

Our bbboost journey continues today with the prototype voltmeter module. Once complete, the bbboost will have a digital voltmeter to accurately measure the output voltage. (And maybe… an ammeter… stay tuned). Over the last week I have been pondering and experimenting on what sort of voltmeter to have. Of course it had to be digital, but what to drive it? First there was a PICAXE microcontroller using a voltage divider and the PICAXE’s analogue to digital converter. Great… except that chip can only use integers. Next…

There seem to be many cheap digital LED voltmeter modules on eBay at the moment, but where’s the fun in that?

Around six months ago I stumbled upon an interesting IC when wasting time browsing through the Farnell website, so I ordered two of them planning to do something with them later on. And promptly forgot about them. However research for the voltmeter showed this chip as ideal – the Intersil ICL7107. An analogue to digital converter and 3.5-digit LED driver all in one. Woohoo!

icl7107

Data sheet is here… ICL7107 datasheet

Furthermore, this seemed like an inexpensive solution, volumes of this IC can be had for ~$2. Good so far, but after studying the data sheet – there was a catch.

It needs positive and negative five volts DC… ah fudge. The ICL7107 data sheet suggests using a CD4009 hex buffer/converter, with some diodes and capacitors. Nope, too hard and messy. However, thanks to the internet a solution was found – the ICL7660 CMOS voltage inverter!

Check it out – ICL7660 Voltage converter

So now the theoretical solution had been found, it was time to move from thinking to doing. Originally I used the circuit diagram from the Intersil web site, however calibration was a problem due to only having a single-turn potentiometer (see parts list below). So for the real unit, a multi-turn potentiometer will be used for R7.

Just a side note… breadboarding circuits can be a joy or a pain. If you use those cheap-ass breadboards from China via eBay, you will suffer. Take my word for it.

Anyhoo, before getting the circuit together, I like to line up all measure all the components – note my trusty capacitance meter …

preparation

Then put them in order according to the parts list. This will save confusion and time later on, as you have checked all the values and ensured they are correct before installation!

prep2

Here is my lovingly-crafted schematic for the voltmeter module. Note that this could be made as a standalone voltmeter, it will measure up to 20v DC. In our finished product, the +5V will be sourced from an LM78L05 voltage regulator.

voltmeter

And the parts list:

  • IC1 – Intersil ICL7107CPLZ
  • IC2 – Intersil ICL7660
  • D1~D3 – 1N4148 diodes
  • LED displays – Agilent HDSP521G 2 x 7-segment green displays (common anode). You can use anything really, as long as it is common anode, and each segment is ~8mA
  • R1 – 220 ohm – all resistors 0.25W
  • R2 – 10k ohm
  • R3 – 1M ohm
  • R4 – 47k ohm
  • R5 – 15k ohm
  • R6 – 100k ohm
  • R7 – 1k ohm multiturn potentiometer/trimpot (for calibration)
  • C1 – 10nF – all capacitors must be rated for at least 25V
  • C2 – 20nF
  • C3 – 470 nF
  • C4 – 100 nF
  • C5 – 100 pF
  • C6,7 – 10 uF electrolytic

Please note that this is a work in progress and errors may have been made, or values altered at any time after publication.

And now for the finished mess:

finished

Wow – what a mess. If you are going to use a breadboard – take care with the very low value capacitors. Try to keep the legs as short as possible to improve the meter stability. When you turn it on, the display will flick a few numbers around until settling on zero. You will need to calibrate it, so just measure a solid, reliable power source (such as the output from an LM7812 and LM7805 (12V and 5V DC) in turn. So when you are measuring the (for example) 5V output from the 7805, adjust the trimpot until the display says 5.00. Try this if you can with a few different reliable voltage sources, to check your new meter’s accuracy.

Finally, this wouldn’t be complete without one of my soundless videos. In this clip, I measure a 9v battery, then an alkaline AA cell, then the same again but with reverse polarity.

So thanks once more for reading. Please leave feedback and constructive criticism or comments at your leisure… and to keep track, subscribe using the services at the top right of this page!

Posted in bbboost, ICL7107, projects, tutorialComments (8)

breadboards and batteries… bbboost

[3 July 2010 – this project has been retired, but the posts left for reference. Not my finest work, but it may help someone]

During my life in the field of electronics study, research, and daydreaming many ideas (good, bad and dangerous) and projects have been constructed using the typical solderless breadboard that everyone has used at one stage or another. There is nothing wrong with this approach, except for the power supply situation. You could either buy an expensive desktop power supply ($40 upwards), use a fixed plugpack (if you have the right voltage) then build some power smoothing into your circuit, or even use a 7805 or similar regulator to get your +5 volts. Failing that, it’s back to batteries.

batteries-and-breadboard

You might as well just throw money into the garbage if you keep using batteries and have AC power nearby. I have had enough of worrying about all of this and have decided to conceive a desktop power supply that meets the following criteria:

  • cheap to construct
  • safe to use (not exposed to mains voltage)
  • can accept any voltage DC plugpack and offer a variable, smooth DC output of up to 1 amp
  • can be mounted on a small PC board with spacers to save money, or enclosed in a housing for a professional look
  • have a digital output voltage meter – so that it looks cool and is convenient. No more guessing with analogue meters and dealing with parallax error
  • increases the constructor’s knowledge of electronics!

Let us call it the bbboost – the bread board booster!

So over the next month or two we will do just that. If you would like to put forward ideas, suggestions or criticisms, please do so. Otherwise, get ready to say goodbye to breadboard batteries…

Posted in bbboost, projects, test equipmentComments (2)


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