[sdiy] dsPIC CV input protection

Tom Wiltshire tom at electricdruid.net
Sat Nov 15 11:58:08 CET 2008

On 15 Nov 2008, at 03:28, Ian Fritz wrote:

> Another approach to consider: amplify your CV so its full range  
> just saturates an opamp.  Then get to 3.3 with a voltage divider.   
> For my SoS wind controller I used LM324 opamps powered at 6.4 V to  
> get a 0-5V swing, which went directly to PIC inputs.

I've been designing a PCB for my PIC-based VCLFO, and that's the  
approach I took too.
I've got a standard op-amp inverting summer powered from +/-15V. You  
can throw whatever you like at that and saturate it if you want to. I  
then followed that with a precision half-wave rectifier stage with  
the feedback resistor set up to reduce the full scale output to  
something safe for the PIC (0-5V in my case). Negative CVs are  
chopped off by the rectifier.

It uses two op-amps, so it isn't a *very* low component count, but  
there aren't many other components beyond the IC, and it seems to  
make a robust solution.


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