Designing a computer based voltmeter

[adrobnis]

I would like to monitor multiple voltage signals at the same time through the parallel, serial or usb port.

The signals can be monitored on a rotating basis based on the speed of switching from one line to the other, however; I am not familiar with how to read the voltage.

For example, I want to monitor the voltage fluctuations on a circuit board, anywhere from 0 - 12 V DC.  How could I do that?

From the programming (software) side, I have a reasonable idea on how to monitor the port, but from a hardware side, I do not.

I appreciate any help you can provide.

Thank you.

[Suraj]

You need an ADC & a microcontroller if you want to put data through USB or serial port. However for parallel port you can get away by using ADC & some logic chips. The selection of ADC will depend upon the resolution you want you can use any 10bit or 12bit ADC with integrated mux for the inputs. You will also need an attenueator at the input to protect ADC.
This is very similar to a Data Acquizition System take a look at http://www.geocities.com/hagtronics/pic_das/

[Ante]

You can get away with a simple ADC and a multiplexer circuit.

[adrobnis]

Thank you both for the information.  I read the information on the ADC but I do not fully understand the process.

Programming the picmicro seems easy enough, but wiring it, knowing what resistance to use, etc., I have not completed figured out.

Can you suggest a location to learn more information or possibly a site with a similar project.

Thank you.

[MP]

...and how were you going to run 12 VDC into the ADC of a PIC? Better figure this into the design, cause the ADC is not going to like more than 5 VDC.

MP

[Ante]

Velleman has a kit with many nice options at a very reasonable prize

[adrobnis]

Thank you.

The K8048 also looks interesting w/ a max input of 20V/40mA on the digital input side.

But, that begs the question - what is the difference between an analog signal and a digital signal when it comes to measuring voltage?

Being the "newbie" I have no clue, however; I would guess analog since the voltage fluctuates, rather than being "on" and "off."  And, in the instance of measuring voltage, I want to know more than just "on" or "off."

Taking that into account, the K8055 only has 2 analog inputs, and the K8048 has 4, both with a potential maximum of 5V.

Again, I am not quite sure even where to start with this project, but I would like to try.

The parameters are to measure voltage from multiple inputs at the same time (or switching between them on the millisecond level is fine) and record the values through a computer program.

Obviously I can take a voltmeter and measure and watch the voltages but only one at a time, and I cannot record the information in a graph format.

So, I suppose you could say I want to build multiple voltmeters which take the information and save it on the computer.

Thoughts on how to tackle this project and/or where to start?

[FRIED]

What resolution do you need?

[adrobnis]

Good Afternoon,

  I am not sure I understand your question.  If you are talking about computer resolution - 640x480, 800x600, or 1024x768 is fine.

  Would that make a difference?

  If you are speaking of something else, please elaborate.

[FRIED]

Bits of resolution for voltage measurement

[MP]

Just thought I would post some ideas for you:
Depending upon the range of input voltage, you could use a voltage divider to scale the voltage down to 0-5. This would limit the range you would be able to measure due to resolution limitations and you would want to use precision resistors with a very tight tolerance.

Another method is to use a voltage to frequency converter chip. Then read the frequency with the pin of a micro or with the PC port.

A third option is to use a voltmeter chip such as the one in our projects section and to read the lines that go to the LEDs as a binary word on the parallel port or a micro.

Hope it is helpful.

MP

[Suraj]

Sorry if i confused you but i have found a better link http://www.qsl.net/zl1bpu/micro/SerialDVM/AVRDVM.htm this projects uses Atmel AVR uC i could not find one using PIC sorry

[MP]

Suraj,
Are you familiar with the project in the link you posted. I saw this earlier when I was looking for AVR based voltmeters, but I do not see how this unit accepts an analog voltage. There is also no source code posted so I was not able to check that. I was hoping you might know something about it.

MP

[Suraj]

First of all i am sorry because i have posted a half-cooked link. The link to bas file is not working . I didn't checked that link prior to posting.
Anyway, the AVR used AT90S4433 has in built 6 channel ADC. So accepting analog voltage is no problem. (however atmel recommends you use Atmega8 insted of it).