Electronics > Beginners
Will this work (optocoupler over shunt)?
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spec:

--- Quote from: ArthurDent on December 07, 2018, 06:45:10 pm ---Here is my final variation of the detector that may address some concerns and, like I said, if any of these various circuits were actually built and tested there could be minor or major changes that might come to mind. I think stenespen now has enough information so they can pick and choose what they think might be best for them and try that circuit.

--- End quote ---

Living dangerously there AD. :palm:
StillTrying:
Isn't anyone going to do an Arduino version. >:D
Zero999:

--- Quote from: spec on December 08, 2018, 11:14:00 am ---Below is the schematic for a precision version, with hysteresis for H99, and an  NMOSFET for AD.

The trouble is that it uses non jelly-bean components, which may not suit the OP.

--- End quote ---
Here's a version which uses jell bean components. The turn on and turn off currents can be independently set if necessary. V2 can be the TL431 or similar voltage reference. It uses a PNP output but it can easily be modified to work with an NPN BJT, N-MOSFET or P-MOSFET.



It's a variant of a circuit I posted earlier this year, which is linked below.
https://www.eevblog.com/forum/beginners/the-simplest-thermostat-with-programmable-thresholds/msg1432025/#msg1432025

EDIT: I haven't included any filtering, which would be a good idea.
spec:

--- Quote from: Hero999 on December 07, 2018, 11:17:27 pm ---
--- Quote from: ArthurDent on December 07, 2018, 06:45:10 pm ---Here is my final variation of the detector that may address some concerns and, like I said, if any of these various circuits were actually built and tested there could be minor or major changes that might come to mind. I think stenespen now has enough information so they can pick and choose what they think might be best for them and try that circuit.

--- End quote ---
That will not overcome the issue of the transistor clipping the comparator's output.

If you want to use the comparator's non-inverting input for positive feedback and don't want to use a MOSFET, then use a PNP BJT, but the logic will be reversed.

You seem not to believe me when I said the relay coil's inductance doesn't generate any noise. Where did you get that idea from? It's compete nonsense!

--- End quote ---
Q2 e/b junction is vulnerable here, as is the open collector transistor in the comparator. Also, you would be losing more drive to the relay than with a saturated collector arrangement, like the original.

Attached is a schematic showing  a simple and safe way to maximize drive to the relay and provide hysteresis (functionally, the TS391 comparator is just a singe comparator version of the original dual twin comparator LM393):

T3sl4co1l:
Vulnerable to what?

I wouldn't recommend running the relay coil wires to the outside world where ESD and maybe surge may be a problem.

Tim
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