I need to hardware-trigger three modules from a pulse signal source. According to their data-sheet each module requires between 5 to 15V for trigger high and 0 to 5V for low. Each module draw around 6mA so the input impedance is around 2.3k.

The triggering source on the other hand is a pulse train at a fixed frequency 32Hz will come from this DAQ hardware sync output. The sync output is only 5V. Here is sync output specs(At 32Hz short duty cycle worries me):

enter image description here

Anyway, the distance from the control source and a module can vary between 10 meters up to 50 meters.

I have two main challenges here:

-The first one is to send trigger from a single source to three modules.

-The second one is the length which can be max 50 meters.

Some suggested to use differential line transmitters with multiple outputs. But the data-sheet of the module says it needs to be 5V and 15V to be triggered. So that means the transmitted differential signal must be converted back to single ended signal right before the module.

Another user suggested to isolate the outputs at the module end.

A while ago I had asked this related question.

One of the answer was simpler to implement. Since it requires less electronics, I decided to try optoisolator way at module ends.

Below is the diagram showing that scheme:

enter image description here [left-click to zoom in]

As you see a DAQ's 5V 32Hz sync output is triggering all three modules at once. Vp1, Vp1, Vp3 separate power supplies for each module. Optoisolator is right before the module. Rg1, Rg2 and Rg3 are just to indicate and simulate that the grounds of opto input and output are isolated. A STP cable can be be used.

It is okay to have some noise or glitch sometimes at the trigger input.

I just need most of the pulses arrive to the module as clean and accurate as possible I can to. Do you think at 32 Hz for around 50 meters length I can trigger those three modules as in the scheme and proper way? What can be modified if necessary?


Photo-darlingtons(4N32) used, a buffer for sync added, STP used:

enter image description here

  • \$\begingroup\$ The opto If current looks a low (what is worst case CTR and allowance for temperature/aging effects?), also I don't see any spec on the drive capability of the source. \$\endgroup\$ – Spehro Pefhany Jun 7 '18 at 19:53
  • \$\begingroup\$ I found more detailed module for the module:scanivalve.com/wp-content/uploads/2018/01/MPS4264_V205-1.pdf At page 23 it says: "The external hardware trigger voltage is input through pins 4 & 5 of the power connector. The trigger is 5-15Vdc, 6.5mA." .. But it doesn't say whether the trigger input has hysteresis. \$\endgroup\$ – HelpMee Jun 7 '18 at 20:30
  • \$\begingroup\$ The source may not drive but I can make a buffer after the sync; that is not a problem, assume it can drive. Im more curious about whether this opto way and wiring correct. \$\endgroup\$ – HelpMee Jun 7 '18 at 20:33
  • \$\begingroup\$ Can you get the 12V or whatever at the far end rather than sending it? \$\endgroup\$ – Spehro Pefhany Jun 7 '18 at 20:37
  • \$\begingroup\$ If you mean placing the power supplies right next to the modules, yes it is possible but then I have to extend the AC mains cables upto there which is okay. \$\endgroup\$ – HelpMee Jun 7 '18 at 20:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.