TrueRMS Digital Voltmeter

[jahonen]

That sounds like a simple solution so I don't waste time calculating too many extra ADC sources.

Here is what my circuit looks like:

http://www.danielbjohnson.net/assets/Uploads/TrueRMS-imagecheck1.png
The image is very large.

I am kind of unsure about the input part but ill think about it.

I don't know if you really meant to buffer the ADC input with 74LS07, but it won't work with analog signals. Use single-supply opamp instead, something like OP777 etc. Also consider carefully the effect of the midpoint scaling network input impedance to divider network, it might have significant effect (just a hunch, I haven't checked it).

Regards,
Janne

[septer012]

  I didn't I just couldn't find the right part, but I have now.

[septer012]

It does affect the circuit but in simulation it has a linear effect so I can math out a good solution.  Now in a real world with temperature differences im sure it wouldn't be a great solution.

[septer012]

Alright thank you everyone who helped me!

I just submitted the final design.  If you are interested in what I came up with, with some of your help of course.

Daniel-Johnson-A2D-TrueRMS-Voltmeter.pdf

[migsantiago]

Maybe it's too late but here you have an RMS function in C language. It calculates the RMS value from an array. I wrote it using the multiple trapezium discrete integration. I have used it on audio signals on a PIC18 microcontroller and it works perfectly.

http://www.todopic.com.ar/foros/index.php?topic=24142.msg238149#msg238149

It's written in spanish but the C code is easy to understand.

[EEVblog]

Alright thank you everyone who helped me!

I just submitted the final design.  If you are interested in what I came up with, with some of your help of course.

Daniel-Johnson-A2D-TrueRMS-Voltmeter.pdf

Nice work!

Loved the "The problem statement left much to be desired." bit. That's the kind of subtle shit stir I'd do!

Dave.

[septer012]

They never called me back that was alot of work! none the less I found a job doing DSP but getting paid as an Intern.

[migsantiago]

They never called me back that was alot of work! none the less I found a job doing DSP but getting paid as an Intern.

Gratz Man!