[sdiy] CV input op-amp circuit

Brian Willoughby brianw at audiobanshee.com
Sat Dec 5 06:33:52 CET 2020

It works so long as there is a protection diode somewhere, connected to the supply reference (ground). As mentioned, *most* uP chips have these, but it's always a good practice to check the data sheet for the "equivalent circuits" for input pins.


On Dec 4, 2020, at 13:39, Tom Wiltshire <tom at electricdruid.net> wrote:
> Yes, the series resistor limits the current flowing when the input voltage goes above the uP’s supply voltage (or above the supply voltage plus whatever the diode drop is in this case - fairly low, iirc).
> So it works for negative inputs too.
> Tom
> On 4 Dec 2020, at 21:07, Didier Leplae <didierleplae at yahoo.com> wrote:
>> How dangerous is it to have negative voltage going to the microcontroller’s pins? I’ve read that it is to be avoided, but I seem to have done it plenty of times without frying my pic chips. Would the series resistor also protect against that?

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