I am working with two industrial cameras that I want to trigger synchroniously through hardware triggering. For this the STROBE_OUT pin (which is an open drain pin) from one camera (Master camera) does trigger the other camera (Slave camera) when an image is taken by the master camera.

The camera manufacturer gave me an connection schematic on how to connect the pins of both cameras. The connections diagram they gave me looks as follows: connection schematic of manufacturer

From the datasheet of the camera I know that the STROBE_OUT pin is a mosfet open drain configuration (pin 2 with corresponding ground on pin 1). The TRIGGER_IN (+/-) pins internal connections are given below (pin 3 and 4):

trigger in connection

This way of connecting it really seems strange to me. In my understanding, when the mosfet is closed the pin 3 of the slave would be pulled to ground, but when the mosfet is open the pin 3 would be in a floating state, am I right? In my understanding this could lead to undefined behaviour?

I would rather assume do a connection with a pull up resistor for example something like the one below:

my connection schematic

(Sorry for that ugly drawing)

Am I misunderstanding something here? What would be the proper way of connecting this?


1 Answer 1


The Slave resistor/LED can be thought of as the pull-up, it is never floating.

This is my understanding of the circuit and how I would wire it based on your descriptions.


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ I think the slave box should be shrunk to exclude the GND wire as there is no connection to it. Otherwise it looks fine. \$\endgroup\$
    – Transistor
    Oct 8, 2020 at 21:33
  • \$\begingroup\$ @Transistor - good point, fixed \$\endgroup\$
    – Mattman944
    Oct 8, 2020 at 21:41
  • \$\begingroup\$ Ah okay, that makes sense :) \$\endgroup\$ Oct 8, 2020 at 22:03

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