Boosting voltage from pins due to wire length

Hello @peekay123,

Thank you for your time and advice. Here is what I did:

  1. I tested each RS485 unit and suspected one was not working so I changed it.
  2. I powered each RS485 unit from a different source per your recommendation.
  3. I generated a square wave per your input. Pin goes from HIGH to LOW every half a second.
  4. On the “receiving” end, indeed I am getting a square output of 5V. So it is working :slight_smile: (thank you).

Now, I unplugged the pin from the sending unit, I was getting a constant 5V on the receiving unit. As I am triggering on a rising edge, I swapped the A&B lines, and now I am getting no voltage when sending pin is not connected and a square output when the pin is. Is this configuration OK to use?

I then tried powering both RS485 units from the same source and the system kept working. As my project will most likely have a common power source for both RS485 units, is this still OK, or do the RS485 units HAVE to be powered from separate sources?

Thanks again for your time.

@Jimmie, the swapped lines are fine. I’m not sure how you expect to power the remote unit from the same supply. Can you elaborate?

Hi @peekay123,

Thank you.

I stand corrected, I meant to say that the two RS485 units will share the same GND because the camera trigger lines will share a GND with the micro that is triggering it.

@Jimmie, a shared GND will create an antenna between the two boards. This will produce GND differential voltages which is not what you want. The camera has its own ground so keep that GND local to the RS485 hardware there. You only need the two RS485 signal pair between the devices.

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OK, @peekay123. I understand it now.

Thanks again for your time and help.

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I would take a different approach and first find out what is happening. If you use a high impedance voltmeter and still measure a low voltage at the end of your wire…with nothing connected, then your wire is bad.
Something is drawing current in your wire or something is still connected at the camera end. (I presume you are using two wires…one is a ground.)

Here in my lab, I can connect a 100 ft spool of fine wire to a 9v battery. Using a good voltmeter (a voltmeter that draws no current) or an oscillosco, I measure 9v at the end of the wire. No current is being drawn.

If I put a 1k resistor between the end of the wire and ground and measure the voltage and the end of the wire, the voltage is now less than 9v, due to the resistance of the wire and the current flowing thru the wire.

Check your wire and connections first. Hope this helps.

George

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Its all about the impedance (effective resistance/inductance/capacitance) of the load the camera trigger circuit represents. Your comment doesn’t provide enough info. And yes as one of the other comments mentioned there is likely a requirement of another conductor to provide more drive capability at the camera end. Also the drive power could come from the camera but that is likely not available. If a power source is available then a single transistor could do the job but an inversion of the action might result. There might be more issues such as isolation and/or inductive load reflections that might occur especially as the cable length increases . A relay (mechanic or even electronic) might provide a superior solution.

Thank you @DenisLebel.