[sdiy] CV input op-amp circuit

Mike Beauchamp list at mikebeauchamp.com
Sun Dec 6 02:29:21 CET 2020

On 12/5/20 4:50 PM, Brian Willoughby wrote:

> That sounds like a good idea. I briefly tried using external clamping diodes for a Euro switch panel, but something didn't work out and I ended up not populating those parts.
> One thing you might have to look out for is that clamping activity will still cause spikes on the supply rails.
> Brian

Very interesting that you had some sort of problem with the diodes. I've 
been unsuccessfully trying to debug a problem I've been having where my 
Teensy 3.2 fails to power on about 50% of the time (the cystal 
oscillator doesn't oscillate) and it seems to go away completely when I 
remove two BAT54S's that are protecting some op-amp outputs that are 
going into ADC pins.

These inputs aren't open to user-voltages so over-voltage scenarios 
aren't expected, but the BAT54S's are there to protect the Teensy 3.2 in 
case something goes wrong.

Unless I can figure out WHY this is happening, I'm probably just going 
to remove the diodes and add current limiting resistors.

My guess is that the voltages spike on start-up and somehow freaks the 
teensy's crystal out.. I know, very technical :)

I've captured the start-up on my scope though, looking at the ADC inputs 
and all voltages and I see nothing different from when the Teensy fails 
or succeeds to power-up.


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