Digital PI

[Peter Morf]

Hi all!

I'm currently working on a digital PI. The idea is to digitally process signals right after the preamp. Don't know if it will be a sucess yet... but this is what the circuit looks like:

https://www.geotech1.com/thuntings/a...entid=23&stc=1

Programming the PIC is not a problem, the analog circuit is my weakness...
Any suggestions? Can this circuit work with proper µC code?

Regards
Peter - Sweden

[Boattow]

Suggestions

Hi,
I just took a quick look at your schematic and 2 things stuck out to me. I would reconsider using 741 opamps in your design. There are much better choices. Also, one of the biggest problems with building a PI detector is having and keeping the power clean. I would look at the 3 terminal regulator's data sheets and look at what they suggest for capacitors on the output. I think you want to add some to the output. I forgot this and it caused me great grief with the regulator oscillating. Check the data sheets.
Good luck,
Boattow

[Carl-NC]

I expect the 741 would not work as the preamp, not enough slew rate. Perhaps those were the default symbol values, and not changed.

I'm a little confused on the second opamp... is it used as an active rectifier?

- Carl

[Peter Morf]

Forgot to say.. LMC6081 is the opamp I planned to use but the Eagle software didn't have the LMC6081, so I placed 741:s instead.. they have the same pin configuration.
The diode at the second opamp is to keep the voltage at -5 to 0.6V. The range of the AD is 5V.
I'll look up the correct values on the capacitors, tnx Boattow.