Connecting open collector outputs to inputs of another device

Discussion in 'The Projects Forum' started by jst, Dec 9, 2013.

  1. jst

    Thread Starter New Member

    Dec 9, 2013
    This is a great forum and has inspired me to take on some electronics projects of my own. Looking for some help interacting some devices together. I’ve got two devices (let’s call them A and B) that need to send a pulses to trigger actions in a third device (since this third device will receive the pulses, let’s call it R)
    Device A has a dry relay output.
    Device B is an open collector output with the following statement from the manufacturer: indicator output provided by open collector outputs, <40 V, 50 mA

    Device R has many inputs, each in a configuration like the one shown in this diagram:


    My question is about what I need to do to connect the outputs of device A and the outputs of device B individually to the inputs of device R?
    It would seem, from my limited knowledge, that if I connect the output relay pins of device A directly to the input pins of device R, it should just work so that device A can signal device R.

    With regards to device B, from my limited knowledge of how open collectors work, it would seem like I could also directly connect device B to device R, but I may be wrong about this. Friends have told me that I should put a logic controlled relay (PDF Link) between device B and device R, to basically turn the outputs of device B into relay outputs. But from looking at that device R input diagram, it seems to me everything is there to just drive this directly (like doesn’t that diagram show a voltage source and a pull-up resister?). Am I wrong?

    I would love to hear the thoughts of the people on this board.
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    Connect a relay contact between GPi#P an Gnd in your diagram, or connect the collector of an NPN transistor to GPi#P and connect its emitter to Gnd, either will pull GPii#P low...
  3. inwo

    Well-Known Member

    Nov 7, 2013
    The open collector outputs can be paralleled if no special logic is needed.

    Any one will activate input.
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
    If R-1 is sensitive to multiple neg pulses, then relay contacts need to be debounced. R-2 , direct connection to collector is OK.
  5. MrChips


    Oct 2, 2009
    The beauty about open-collector outputs is that you can parallel multiple control signals to create a WIRED-OR function without the need for extra gates. This works for NEGATIVE LOGIC (i.e. ACTIVE-LOW signals). Any LOW signal asserts the function.