Latching LED

Discussion in 'The Projects Forum' started by cjhaddenjr, Jan 26, 2012.

  1. cjhaddenjr

    Thread Starter New Member

    Jan 26, 2012
    I'm new at this as I'm now retired from working as a plant electrian where I troubleshot more than design circuits.

    I'm wanting to modify a store bought driveway alert I bought fron Harbor Freight tools to be able to latch the output of the reciever or part of it on when the transmitter detects motion. The output of the reciever consits of three 1.5 volt red LEDs and a audible alarm. For some reason two of the LEDs are switched on by a 9013 NPN transistor and the other LED is switched by a 9014 NPN transistor. The reciever is powered by 3 c cell batteries@1.5volt each in series.

    I'm thinking of a small SCR being gated from the 9013 and reset by powering system off.
    Will this work or what do you'all think?
    Thanks, Curtis
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
    Please tell us how the LED is connected to transistor, I assume to the collector?

    What is the value of the resistor in series with the LED?
    What is the base resistor value?

    The solution could be as simple as a PNP as a latch, providing base current to the NPN after triggered. That would be a PNP, two resistors and a diode.