Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Latch to quick 3V signal with SR latch

  1. Jan 12, 2012 #1
    I'm a beginner at electronics, so please bear with me...

    I have a 3V signal that is triggered under a certain condition and stays on for less than a second (I have no control over this). This is connected to a DAQ that can only sample at very slow rates (Also, no control over this). I'm trying to build a quick and dirty external latch circuit that will allow me to register this quick 3V signal and then "latch" on to it so that it can be registered by the DAQ (which samples at 1 sample per minute more or less)

    My idea is to use a SR latch with the SET connected to a lead that connects to the terminal that outputs the momentary 3V signal and the RESET connected to any low voltage source. This way, when the 3V signal goes off, it will be latched to 3V and be able to be recorded by the DAQ when it finally gets around to sampling it.

    Am I on the right track? Thank you.
  2. jcsd
  3. Jan 12, 2012 #2


    User Avatar

    Staff: Mentor

    Welcome to the PF.

    Yep, that's the way to do it. You can use an SR latch or some variant of a flip flop. The DAC unit should clear the latch at the start of everything, and clear it after it has read the high value.

    You could get into a little bit of a race condition where the DAC is clearing the latch at the same time as the signal is coming in. If this is an issue, you could use two latches both watching for the incoming signal, and sample/clear them separately at slightly different times from the DAC unit.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook