Latching interface logic required

Discussion in 'General Electronics Chat' started by grahambollan, May 27, 2007.

  1. grahambollan

    Thread Starter New Member

    May 27, 2007
    2
    0
    The problem is to take a 9volt pulse from a clock and produce a 'loop' to operate a pump, this loop has to stay on until a second pulse from the same source signals a disconnect to the 'loop'. This process is repeated during the operation of a automatic sprinkler system where the clock output operates latching relay operated valves. I tried obtaining a single coil latching relay but to no avail. No other signals are involved, the 9volts pulse is battery derived and the loop will operate a relay in an artesian pump panel. Any bright ideas using common parts (I'm living in Turkey and component shops are thin on the ground) would be appreciated. Thanks for struggling through all this :)
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    If you have enough relays, you can make a ladder logic version of the JK flip-flop.

    http://www.allaboutcircuits.com/vol_4/chpt_10/6.html

    You might be able to find a logic level flip flop such as the 7476. They've been around for decades, and might have found their way to a supplier near you.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    You would be better off using CMOS logic like a CD4013 - the TTL 7476 will blow up with more than 6 volts applied.
     
  4. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    This sounds like the classic Battery Operated Irrigation Controller, which uses Latching Soleniods to control water.
    If this is actually the case, then the output from the timer is a +9 volt pulse which latches the solenoid on, and a -9 volt pulse which latches it off.
    The reason for this is so that the battery isn't flattened holding the solenoid on during the irrigation period. It also means that if you have a decent enough supply that will handle holding a relay in an ON state for the pump, that you would be better to invert the negative pulse and therefore have 2 separate pulses to work a basic S/R flip flop. This would have the advantage of not allowing a confused output state in the event of error, reset or power cut.
     
  5. grahambollan

    Thread Starter New Member

    May 27, 2007
    2
    0
    Thanks to all of you for the ideas, the irrigation system is the right scenario, I'll now try the suggested solution. All I need is to find a component store in Turkey!
    Good luck to you all!
     
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