Latching and unlatching with a long pulse

Discussion in 'The Projects Forum' started by tnorth, May 29, 2008.

  1. tnorth

    Thread Starter New Member

    May 29, 2008
    [SIZE=-1] I am trying to build a latching relay for a remote setup. What I am doing is sending a tone over a radio with DTMF, it decodes the signal. The decoder sends out a minimum 10sec pulse. I want to use that pulse to turn a device on and off. So one 10 sec pulse will turn it on, another 10 sec pulse will turn it off, and so on. But I cannot seem to find a easy way to do this. All I have to work with is one output going Low to a High condition for 10 seconds. I need that to trigger a permanent on/off condition over and over as I turn the device on and off remotely with that 10 sec pulse.

    I am wondering if anyone knows a place I can get a latching device or build a simple circuit that can latch and unlatch by recieving the same input. Thanks.
  2. Wendy


    Mar 24, 2008
    Do you have the 10 sec. pulse to work with already, or do you need to generate it also? The 555 has several circuits that pertain if we're dealing with an existing pulse already.
  3. mik3

    Senior Member

    Feb 4, 2008
    You can use a T flip flop (Toggle flip flop). This flip flop every time it receives a pulse it toggles between a high logic and a low logic. In this way, you can set the output of the T flip flop to a high logic with a pulse (turn your device on) and on the next pulse you will reset the flip flop to a low logic (turn your device off). Also, because the flip flop has two complementary outputs (they are in opposite logic states) you can control two devices and turn the one off while you turn the other on and vice versa if you like.
    If you have a JK flip flop available you can make a T flip flop by applying a high logic at its J and K inputs and use the Clock input for the pulses.
  4. ffl

    New Member

    May 29, 2008
    I also have the same type of problem. My input pulse is 5vdc and I need to turn on or control a 12vdc coil till it is turned off by the same 5vdc pulse.

    I am not a electronics person and need a design to mfg the circuit. Please help