I have an open collector output interfaced board using that how should I control an input of another equipment with below characteristics:

0 Ground 1 Open


  • \$\begingroup\$ Maybe I'm just tired, but I don't understand the situation. Could you elaborate? Post a schematic maybe? \$\endgroup\$ – Sean Boddy Feb 28 '15 at 7:24
  • \$\begingroup\$ Hı Mr Body, an equipment says i have an digital input as I mentioned. And i have a open collector output board so how should the connection must be. Directly or with relays or somehow? \$\endgroup\$ – Soso Feb 28 '15 at 7:27
  • \$\begingroup\$ I'm not sure if we're talking about the input or the output now. A digital input should be driven by digital logic with the correct voltages. An open collector output can be used to connect anything it can handle. And what you connect it to depends on what you want it to do. What do you want the output to accomplish? \$\endgroup\$ – Sean Boddy Feb 28 '15 at 7:34
  • \$\begingroup\$ I want to control equipment one of the interface and above i gave information given by interface document. Lets forget about open collector what you understand from that interface specs and how you control it. \$\endgroup\$ – Soso Feb 28 '15 at 7:39

I'm sorry i didn't understand sooner. Your open collector output could just be connected directly to this kind of input, because the input is already arranged to use an open collector. Although, it looks like you might have to invert the logic to get the desired response, which can be done with the addition of another switching transistor.

  • \$\begingroup\$ Thanks Mr Boddy for the answer.Is this digital input signal push pulled internally what can we say about that. \$\endgroup\$ – Soso Feb 28 '15 at 8:28
  • \$\begingroup\$ Based on the specifications given, the input almost certainly enters the base of a transistor that has an internal bias voltage with a pull up resistor. Grounding the input removes the bias voltage and forces the input transistor off, presumably creating the logic 0 as listed. \$\endgroup\$ – Sean Boddy Feb 28 '15 at 8:33
  • \$\begingroup\$ If possible i will ask for recommended links for this working principle, if not thanks again. \$\endgroup\$ – Soso Feb 28 '15 at 8:37
  • \$\begingroup\$ This kind of digital input is called a sourcing input, which requires a sinking output to drive it. It provides its own voltage and can used in a multitude of different ways, and can easily be used to create wired logic - for instance, multiple open collector outputs could be directly connected to create a logical OR, or the path to ground could be blocked by multiple switches/relays/transistors, creating a logical AND. The only real disadvantage is the amount of power consumed by triggering it, which is still minimal. \$\endgroup\$ – Sean Boddy Feb 28 '15 at 8:57
  • \$\begingroup\$ Many thanks Mr Boddy. Last question: digital input is one pin, but my open collector has 2 pin( with discrete output return). So what must be done. Should I take equipment supply return, analog return, or what? \$\endgroup\$ – Soso Feb 28 '15 at 9:07

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