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I need to trigger a camera using a 3.3V signal, the camera is at the end of a 3 meter cable. This camera has two trigger inputs, a 3.3V GPIO input and an optocoupler input with max input of 30V. I guess that the 3.3V signal will not work with a 3 meter cable so I should use a higher voltage. I happen to have a 24V power supply available. So I guess it will be better to trig the camera using a 24V signal. If I'm right, how can I easily convert the 3.3V signal into 24V? The trig frequency is just a couple per second so I don't think I need a especially fast circuit.

EDIT: maybe it would be better to lower the 24V to something lower like 12V or 6V, right?

The circuit on the camera side is:
enter image description here

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    \$\begingroup\$ 3.3v will be fine over 3m \$\endgroup\$ – MadHatter Nov 5 '19 at 19:27
  • \$\begingroup\$ Its an electrically noisy environment and the testing I made some time ago, I lost some trigs and got a few unexpected ones. \$\endgroup\$ – Pedro NF Nov 5 '19 at 19:46
  • \$\begingroup\$ Try a 100nF cap in the connector, camera side, and a ferrite clamp on the cable. \$\endgroup\$ – bobflux Nov 6 '19 at 0:51
  • \$\begingroup\$ Use shielded cable. \$\endgroup\$ – MadHatter Nov 6 '19 at 1:52
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    \$\begingroup\$ @PedroNF Do you know what the current limiter does in terms of limiting the current? (It's probably a very safe level. I'm just wondering if they provide a spec for it.) Separately, why not wire the +24 V at your remote end straight to pin 2 over the cable and then switch the low-side (pin 5) to your MCU ground? Just a simple NPN BJT or NFET should be able to handle the opto-current okay and it doesn't require any fancy 24 V footwork -- just a BJT or FET that can stand off the 24 V (which most can do.) \$\endgroup\$ – jonk Nov 6 '19 at 6:07
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This. Unsure if your opto input already includes that resistor.

Make sure to pick a MOSFET with a rated RSdon for a Vgs of at least 3.3V, and that it's source-drain voltage can withstand at least 30V.

Might want to connect a TVS diode from gate to ground too since it sounds like this thing can be unplugged leaving the gate vulnerable to ESD.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Yes, the cable from the trigger device to the camera can be disconnected. \$\endgroup\$ – Pedro NF Nov 5 '19 at 23:48
  • \$\begingroup\$ Just edited the question to include the camera side circuit, apparently there is already a current limiter so no need for a resistor. \$\endgroup\$ – Pedro NF Nov 5 '19 at 23:53
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I ended up using the circuit below and its working ok.
The line coming from the left into R3 is the 24V power supply.

enter image description here

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