From: Justin Richards <justin.richards@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Sun, 13 Sep 2020 05:42:31 -0700
Subject: Re: [EE]: OpAmp Max differential input voltage GL358
Thread-Topic: [EE]: OpAmp Max differential input voltage GL358
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Update:
The system as proposed appears to be functioning as expected.

The ADC readings are plagued with low level noise but this is generated
from the ESP8266.  I think this is while it is WIFI'ing, but it is so
minimal I don't feel the need to chase it down.

There was a minor gotcha.  The OFF time before sampling needed to be
increased to 1/50 * 1/2 +abit or slightly over 10mS worst case.  This is
because the TRIAC latches until the next zero crossing.  At 50Hz this could
remain latched for up to 10mS from when the ESP8266 output pin is
tri-stated.  Obviously a ADC sample while heating yields bogus readings so
needed to be avoided.

In reality, the system regulated ok without any concern with 'OFF time
before sample' as the two events (i.e sampling and heating) rarely and
randomly coincide and therefore the undesirable effect of sampling while
heating averaged out.

There are other approaches that could be taken to ensure that the sampling
never coincides with heating but it does not seem to warrant the effort.

Surprisingly, the random selection of feedback resistors, resistor dividers
and the circuit in general produced ADC readings where  ADC/2 was fairly
(scarily) close to the actual temperature in degrees C at or around the
normal solder melting temperature of 183degC.  Was not expecting that.

Thanks for all the input.

Regards justin
--=20
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