Help with Circuit

[Art]

Hi Guys,
Not PBP specific, but I'm trying to make a pic powered voltmeter using an LCD display and Pic 16F876.
and then hope to go on to log voltages, display averages, predict battery behavior, etc.

A couple of the panel voltmeters sold at Jaycar are powered from the line being measured.
I'm wondering if they go about this by regulating the line with a 7805 or similar to power the device,
and then also feed the unregulated side of the 7805 through a voltage divider,
and then straight into one of the ADC channels without being regulated???

Also.. I have an ADC variable being readout to LCD for experimentation.
The LCD shows zero when the ADC is grounded, and 255 when connected to +5 Volts.
Is this what I should be using for a voltmeter? (once some calculation is done)
Cheers, Art.

[mackrackit]

Do you have a data sheet for that Jaycar part or a part number?

8 bit or 10 bit?
Hard to say. Depends on the resolution you want.
Here is something to look over.
http://www.rentron.com/serial.htm

[Art]

Turns out I might by lying about the Jaycar panel meter.
Looking back, I found a picture with a 7805 I used to power it.

It's a 10 bit ADC I think since it's a 16f876.
I have it working as far as it returns 0 if the ADC line is grounded,
and 255 if It's connected to the pic circuit's 5 Volt power.

Re: your link, I've seen many 5 Volt Voltmeter circuits on the net,
but this is to operate in the range of 12 Volt batteries.
I've found a few hints about that on other forums.. ie:

Ok, so you've decided on 0.1V resolution. Set the A-D ref volt to 5V and construct a voltage divider on the A-D input with a mid-point voltage of 5V when 25.5V is applied at the top-end e.g 15k fixed resistor at the top, 10k multi-turn pot at the bottom and take the output off the wiper. (you can refine this but just as an example)

I believe the PIC has a 10-bit A-D converter so RRF the result to give an 8-bit result. You now have a 0-25.5V voltmeter with a 0.1V resolution and a direct relationship between the value returned by the A-D and the input voltage i.e. 125 = 12.5V, 147 = 14.7V ....

I have sound now, and an I2C EEPROM for logging. I'm just ready now to play with voltage dividers
to prepare a voltage input.

[mackrackit]

Yup, a voltage divider is the way to go.
Do a search on this forum and what you are planning has been talked about.

The link I referred to was more for the ADC explanation part and not the circuit.

[Ioannis]

I wonder why did you solder components on the copper side of the board.

Ioannis

[Art]

I always surface mount everything on prototype boards.
I like to have one flat side sitting on the desk.

I have a working Voltmeter unit now
It also has an interrupt/timer driven real time clock.
I guess the next thing is to start the logging, and make it smarter.