ICL7106 Voltmeter

[gregmcc]

I'm trying to build a voltmeter based on the ICL7106 to use with my adjustable power supply. I've got a circuit from Quasar Electronics (https://www.electro-tech-online.com/custompdfs/2007/03/3127.pdf)

I've got the circuit built and am powering it from my 20V power supply via a LM7809

Now on the output of my variable supply I want to connect it to the "voltage in" on the diagram. So I've connected the minus to the same ground point as the 9V input ground - and thats where things go wrong - it only displays a "1". If I disconnect the grounds it kinda works. The only thing I can think of is the input supply GND and the "voltage in" minus must be seperate.

If this is the case how would I connect it to my power supply. Also the voltage I do see on the LCD jumps all over the place.

Can anyone suggest a course of action - does the circuit look fine. Should I look at another one - I've seen a few using + and - 5V?

 

[Nigel Goodwin]

You need a completely seperate 'floating' supply to feed your meter module, you can't feed it from the supply it's measuring.

 

[gregmcc]

Thanks - that explains why its not working
How do I go about creating one from my power supply?

 

[Nigel Goodwin]

You add an extra small mains transformer, rectifier, and regulator to feed it.

 

[gregmcc]

Not a problem - off to the eletronics shop today.

Is that the most effective way/only way of doing it? Is there no magical IC you can use dto do the same thing?

 

[Sceadwian]

I'm sure there's a way to do it with a switched capacitor bank but a transformer is much simpler.

 

[Nigel Goodwin]

Not a problem - off to the eletronics shop today.

You could try running it off a battery first!.

 

[QuasarElectronics]

3.5 Digit LCD Panel Meter (3127) from Quasar Electronics

We are always pleased to see industrious hobbyists building electronic projects from scratch - we have all done it!

For those who do not want to source all the individual components and layout and manufacture a one off board there is a much easier and professional looking solution. Hurrah, I hear you say. Just mosey on down to **broken link removed** and buy the **broken link removed** direct from us either as an electroni kit or if you are really busy you can even get it as a pre-assembled electronic module.

Yes, we know it might cost a bit more and maybe it isn't such a challange or quite as rewarding as the DIY route but then you did get the job finished in half an hour not one and a half days and now you can get on with something more interesting instead.