36 Replies Latest reply on Apr 4, 2018 12:16 PM by anishkgt

    Detecting OFF state of an AC Load


      Hi All,


      I am trying to switch on a LOAD from its OFF state by detecting a change in the voltage. Here the load is a MOT, the voltage at the primary is 1VAC when OFF.


      My idea is to switch ON the MOT by detecting the voltage change at the primary when the Secondary are shorted. I can see a voltage drop of .5VAC when shorted. How can i monitor this voltage change with an Arduino.


      My solution to the problem is shown below.

      The Live of mains is connected to the MOT through the LIVE_LOAD in the schematic. During the OFF state the Optocoupler is triggered so that the 1VAC is seen by the Precision rectifier LT1078 and is rectified and send to the Analog pin A0 on the Arduino. With a code i could detect the voltage change and use it trigger the MOT again and at the same disable the optocoupler to break the circuit to the LT1078. Basically eliminating the need to press a switch two switch ON the MOT.


      is there a better way to get this done. I was thinking of using the basic 1N4007 to convert the 1VAC to dc but that would be a problem when the MOT is switched ON allowing the mains 240VAC to flow through the DIODE.