0-1000mV meter (Help!)

[rene]

Hello,

I have a 16F887 with an LCD display which is now a 0-5 voltmeter and this works fine.
But now I would like to make a voltmeter that can measure 0-1000mV.
How do I do that???

I know something as Ref+ can be used by example to offer pin5 1.024 volts ... but to me it does not work.

Does anyone have examples of software and hardware please.

Thank you ...

Rene

[kersing]

Hardware: you are trying to use the chip out of specifications. If you check the data sheet for the 16f877, page 174 parameter A20 states: Reference voltage (Vref+ - Vref-) should be at least 2 volts. So using a reference voltage below 2 volt is out of spec for this chip.

Software: you could start by trying to write the program with Vref Option set to Vdd. That should at least produce a value <> 0 for a voltage near 1 volt. If that works you can try Vref = Vref+ and use 5V on pin 5.

If you post your flowchart we can take a look at it and try to find what could be wrong...

[rene]

A ha...out of spec..

All I need is a simple voltmeter that shows a input 0-1000mV on a display.
0-5 Volt succeed ...with no problems

I've ordered a 16F1937...
This has an internal ref voltage of 1.024V ..

How to use this in flow code, I still have to find out.
Has anyone experience, ideas or tips ...

cheers,

Rene

[Enamul]

Hi
I think you can still measure 0-1000mV with standard IC and simple PIC program..For example, you have a source which can provide Vout varies from 0 to 1000mV..just need to put a 5 gain non-inverting amplifier in front of that and feed to An0 of PIC.
You can see the attached in hardware..