We have a project where we are creating a printed circuit board that will interact with a commercial washing machine's mechanical timer. The circuitry has to be able to read when 115VAC is present or in the case of a 230VAC machine when 230VAC is present. Is there more than one approach when it comes to picking off that part of the logic within the circuit board. Since I am the person underwriting the project ... I am hoping the relatively young electronic engineer is not in over his head when it comes to the most reliable & durable way of reading the presence of the proper voltage. We are hoping to use the same components on that part of the board for sensing either 115VAC or 230VAC so we do not have more than one prototype for the board itself.

Thanks! --- Mike

 

U are planning to use live voltage with logic. Hope u know wht u are up to.

Heads up !!
Read the rules of AAC lately

There are ways though. I dunno how long this thread will remain open.
This is what I will do.
Design a comparator operated in mains level and use opto's to couple to logic circuit. Of course there are other ways. The difficult part is Live circuit comparator.

 

A small transformer. You will by any means isolate the logic board from the mains

 

While there are dependable ways of doing this without a transformer I am forbidden to discuss these under our terms of service.

This is because we have many young or inexperienced people reading this material and we don't want anyone to put their eye out.

If your people are building their own power supply for this (a tossup... a pre-built tested working complete assembly may be available for less then you can buy and build one) (think of a wall wart low voltage transformer) then the output of the transformer can be used fairly directly as a source to measure the line voltage, at the point it is supplying the supply capacitor(s). This voltage is directlyproportional to the line voltage, and can be simply read by many microcontrollers... or even an analog comparator.

 

Use an optocoupler with a series resistor, something like this:

http://www.digikey.com/product-detail/en/MID400S/MID400S-ND/401769

 

Good idea, but I would make it a voltage divider instead of just a plain resistor.

With the right 2 resistor values the opto LED (1.2v) would not turn on at all unless the 220v supply was present. And if AC, obviously would only turn on the LED on the peaks of the 220v AC waveform.

 

Put a very small 220 volt bulb inside a box with some proper light sensor. If the voltage is 220 the bulb will light up. With 110 volt it will be very dull. Quite crude device but for a school project OK