120vac or 240vac input design to trigger logic on PCB

Discussion in 'General Electronics Chat' started by steward, Oct 7, 2014.

  1. steward

    Thread Starter Active Member

    Jan 21, 2011
    38
    0
    I am helping to design & build a revision to an existing mechanical timer washing machine that needs to have components & logic that do the following: There are several 120vac or 240vac solenoid coils that come on at various times that the logic must be able to see the voltage presence as a trigger for the logic to respond based on the time of the voltage present.

    Any ideas on what the best approaches to that kind of notification to the logic of the add-on printed circuit board?

    Mike
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
    2,373
    Not quite sure of your intention here?
    Are the solenoids energized outside of the timer but you need to monitor when they are on? Or?
    Max.
     
  3. #12

    Expert

    Nov 30, 2010
    16,298
    6,811
    A schematic is worth 10 characters.
     
  4. steward

    Thread Starter Active Member

    Jan 21, 2011
    38
    0
    Max,

    The solenoids are energized outside of the brand new prototype printed circuit board with the programmable logic. So you are correct in understanding that the logic will be monitoring the presence of 120vac at specific solenoids or in the case of the bigger washer it will be the presence of 240vac at specific solenoids. The existing space age type of plastic proven trouble free washer timer is actually outputting to the solenoids. The project is to make the washer more user friendly with a backlit LCD showing time remaining & also to modernize the controlling of the number of fills & other new features.

    I am posting to see if there are other practical approaches for having logic on a PCB check the presence of those 120vac or 240vac line voltages besides the schematic that #12 shared.

    I am also wondering about the best components for outputting 120vac or 240vac from that same PCB. The outputs would be only about 11 watts of of energizing solenoids if that info helps.

    Mike
     
    Last edited: Oct 7, 2014
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
    2,373
    Last edited: Oct 7, 2014
  6. #12

    Expert

    Nov 30, 2010
    16,298
    6,811
    Many ways to skin the cat.
    You could use a current transformer or a 240V to (low voltage) transformer and rectify the results of those, or you could use a diode and a resistor to drive an opto-coupler. These 3 methods will provide galvanic isolation if you need that.
     
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