help with Comparator design

[anishkgt]

Hi All,
Forgive me for this silly design and questions. I am just getting started with comparators i understand the basics of comparators but need some help understanding it when applying this in real life.

In the schematic the voltage is sensed during the off state of the transformer via an optocoupler only sensed when the mains voltage is OFF via an arduino. The voltage is 1.05vac, this is sensed by a comparator and it is compared to a reference voltage of 1vdc. My normal voltage at the open circuit is 1.05vac and when the secondary are shorted it is 0.5vac, i wish to detect the voltage drop and trigger a MOT via an SCR controlled by an Arduino.

The idea here is to detect when the secondary are shorted.

Thank you in advance.

[danadak]

In an Arduino you could do this mostly in code, using A/D. You
would have to offset the AC signal into Arduino, or just use 1/2
the sine and use diode clamps to insure you do not exceed rails.
Thats a -

AC Source >> Resistor (1K) >> Diode to + rail & diode to - rail >> Arduino input.





In Arduino just sample input and code for peak detect.


Regards, Dana.

[anishkgt]

Thank you dan !

Could you please explain with a bit more clarity. Trying to make it as simple with least BOM and safety in mind (preferably an isolation like an opto-coupler)

[danadak]

In this ap note is an interface circuit.


http://www.cypress.com/file/157911/download


Here are some approaches for power supplies but show general considerations for AC line interface,
transformerless.


http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf


https://www.edn.com/design/power-management/4418393/AC-power-your-circuit-without-a-transformer


http://www.farnell.com/datasheets/1930673.pdf




Regards, Dana.