PIC Voltage Meter

[iflymyhelishigh]

Hi guys, I am working on a PIC Voltage Meter. Apparently I should be using a PIC with a Analog input, and I have chosen a PIC16F88 for that.

I want to measure voltages up to 12 volts, and display it on a 16X2 HD44780 compatible screen. Apparently I need to have a resistor voltage divider for that, is there a formula to come up with the resistor values I need?

What do you think I will need for this project? I am thinking just a very simple PIC itself, resistor voltage divider, and LCD screen. The power supply I am using to monitor the voltage has a 5 volt output, so I am covered with the voltage supply.

Thanks guys, iflymyhelishigh

 

[Nigel Goodwin]

Check my analogue tutorial, which explains all you need to know - and is very easy to move to a 16F88.

I would advise an opamp buffer (as my tutorial uses) because the analogue inputs need a low source impedance.

 

[Noggin]

Check my analogue tutorial, which explains all you need to know - and is very easy to move to a 16F88.

I would advise an opamp buffer (as my tutorial uses) because the analogue inputs need a low source impedance.

If the analog voltage is slow moving, a 0.1uF cap at the PIC's input should be plenty enough to swamp the sample and hold cap.

 

[iflymyhelishigh]

Hmm, is there a difference between a LM7805 and a 78L05?

EDIT: 50th post

 

[Mike - K8LH]

The Data Sheets are usually a good place to start...

 

[Nigel Goodwin]

If the analog voltage is slow moving, a 0.1uF cap at the PIC's input should be plenty enough to swamp the sample and hold cap.

And would make the situation massively worse - so how would that help?.

If the input is slow moving it doesn't matter anyway, as long as you're not switching inputs - if you do, you have to allow time for the capacitor to charge or discharge.