Reading an analog current signal into a pic micro

Hi all,

I have 2 H bridges that are powering two DC motors. The total current going into the motors (5A) is being measured by an INA193. I want to read in the average current (RMS would be better) going into the motors. For this I am low pass filtering the current output using two LPFs in series. I am using the attached circuit but the values are not quite stable. What can I do to solve this?

I am also open to doing some calculation in the micro which is a PIC18f4431 run at 10MIPs. The problem is that the process slows down when I try to average the values using the code. I am also running a motor speed PID loop inside the micro.



Regards

I think the PIC wants an input impedance of 2.5k or less, so you should size your filter to match that.

Thank you for the reply ronv !!!

The input for the PIC goes from "IOUT" connection from the U12 opamp output so I don't think the input impedence is high.

Regards

Ooops! I was reading it backwards. Seems like it should be ok. What does it do?