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I need an isolated closing contact, like a relay, but ideally solid state. Rating 24V 100 mA on the contact side would be plenty. 1 kHz operation would be enough as well. I will drive this from 5V 25 mA gpio pins. Ideally with a <10 mA draw!

I've looked at optocouplers, but the ones I can find put VCC on the transistor/contact side; I'd need one with that side having only contacts.

The application is a remote camera trigger with both pre-trigger and trigger inputs, so two channels needed although two singles is fine.

Is there some kind of component or variant I'm missing?

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  • \$\begingroup\$ I have no exact part numbers, but a solid state relay is probably what you want: en.wikipedia.org/wiki/Solid-state_relay They are pricey, but the well designed ones have no link between the "coil" side and the "contact" side, and are able to switch AC and Dc voltages with no issues. \$\endgroup\$
    – Kris Bahnsen
    Commented Aug 27, 2013 at 16:33
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    \$\begingroup\$ There are MOSFET-based optocouplers that come in 6-pin DIP packages and have the ratings you need. I bought mine from Digi-Key, but I don't have a specific part number at hand right now. \$\endgroup\$
    – Dave Tweed
    Commented Aug 27, 2013 at 17:01
  • \$\begingroup\$ What "closed contact" resistance and / or saturation voltage can you tolerate? 0\$\Omega\$ and 0volts is unrealistic as an answer! Why the need for the isolation - what voltage are you wishing to isolate or maybe what physical distance across a PCB? I've seen devices that are good for doing this but have a 3ms switch time as do quite a few SSRs. \$\endgroup\$
    – Andy aka
    Commented Aug 27, 2013 at 17:02
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    \$\begingroup\$ What camera is this for? \$\endgroup\$
    – JIm Dearden
    Commented Aug 27, 2013 at 17:32
  • \$\begingroup\$ In case someone has other good ideas: It's for an N3 connector. The isolation is not across a PCB, as much as between PCB and external connector which may not share ground. A few hundred volts of isolation should be sufficient. I can tolerate at least 0.3V saturation voltage and/or 5 Ohms of on-resistance. \$\endgroup\$
    – Jon Watte
    Commented Aug 28, 2013 at 0:17

1 Answer 1

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Let's assume this is for a Canon camera (other types are available).

The auto focus is the first switch (pre-trigger), the shutter is the second. Both are operated by taking the signal to ground. This can be done by a push to make switch, a relay contact or more simply by a transistor. Depending on the particular model you will require a 2.5mm jack plug or an N3 connector. A typical interface circuit using opto isolators is shown below that can be manually operated (Sw1,2) or controlled by 2 * 5V gpio lines.

enter image description here

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  • \$\begingroup\$ This is for an N3 connector. The bit I was looking for was the "4N25" part number. The optocouplers I've used before (6N137,) and the ones I found through controlled browsing of Digi-Key, need a VCC which comes from the "outer" side. \$\endgroup\$
    – Jon Watte
    Commented Aug 27, 2013 at 19:14

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