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?
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?