[sdiy] CV input op-amp circuit

[Brian Willoughby]

Yes, these sorts of problems can be all too common.

An early prototype of a PIC-based platform would reset at random. Turns out that the reset line had to be buffered "just right," or else even the slightest field would cause the PIC to reset. Once I discovered the problem, I could wave my hand over the PCB and get it to reset! Prior to that, I had a hard time correlating the unexpected problems to the conditions.

Brian


On Dec 9, 2020, at 11:51, Jay Schwichtenberg <jschwich53 at comcast.net> wrote:
> Mike,
> 
> You might do some research on the Teensy 3.2 (https://forum.pjrc.com/). There are some power on issues depending on the power supply, if I remember correctly it's slow power up thing. On the uO&C they had to add a reset manager to get it to power up all the time. Might look under uO&C on Muffs too.
> 
> Jay S.
> 
> On 12/5/2020 5:29 PM, Mike Beauchamp wrote:
>> 
>> 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.
>> 
>> Mike