Reading an analog current signal into a pic micro

[dmta]

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

 

[ronv]

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

 

[dmta]

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

 

[ronv]

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