[sdiy] Protecting PIC A2D inputs from large CVs

[Tom Wiltshire]

Hi All,

I *know* we've discussed this topic before, but I've done a little  
circuit that provides a CV mixer and limits the output to 0-5V for a  
PIC's A2D inputs.

http://www.electricdruid.com/PIC_CV_Mixer.gif

It's yer basic CV mixer, followed by a precision rectifier that also  
attenuates the output. This cuts off all negative voltages, and  
reduces +15V to +5V.

There's a cap marked on the CV mixer to limit high frequency  
response. Adjust to taste. Diodes are basic 1N4148/1N914s. The CV  
input is marked -5V to +5V, but you can throw up to the full supply  
range at it without causing any problems.

Also bear in mind that this feeds voltages up to the rails into the  
amp, so you need an amp that can handle that and provide a rail-to- 
rail output. But then again, if it can't ,no biggie - you just lose a  
little off the top end of the range.

It's all pretty straightforward, so it should be good for tweakers.

Any thoughts or suggestions welcome.

Thanks,
Tom