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I've managed to "build" a shutter release for my Canon SLR by shorting two wires connected to the appropriate pins on the Canon connector. I am looking for ways to extend this into an intervalometer using an Android smartphone.

I've already asked this question about how to do this with using the USB jack on the phone, but I'm now wondering if this can be done using the headphone jack on the phone. Essentially, I would be playing a fixed frequency audio sound on the phone so as to not change the voltage and current going through the wire.

Would it be possible to use something like a relay (solid-state or otherwise) to short the pins on demand (i.e., when audio is playing)? I'm asking about the relay because that is what my Google-fu turned up, but other suggestions are welcome too.

The conditions remain the same as the other question, i.e. no hardware mods to the cell phone or camera and the solution has to be cheap ($4-5) without the headphone cables, connector, wires etc. because I can salvage those.

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  • \$\begingroup\$ Note an audio signal is a variable voltage. A DC signal (what you need to activate a regular relay) is a signal with a frequency of 0. Unless you have some way of allowing your phone's headphone amp to output a "high" output, there's no way you'll be able to activate a relay by playing an audio signal. I very much doubt you'd have any way of playing an audio signal to generate this (however, there may be other ways to interface with the headphone jack to output a suitable signal). \$\endgroup\$
    – Shamtam
    Commented Dec 1, 2012 at 1:20

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Neat idea. I just finished building a Bluetooth controlled Canon SLR remote, but it's controlled from the phone, not by the phone.

I think you can use this idea to drive the input to a MOSFET (a 2N7000 should do). When the signal from your phone drives the opamp high, the MOSFET will act like a switch, shorting your shutter release pin to the camera/circuit ground. If it turns out that the signal is too short in duration for the shutter to fire, just use a 555 in monostable operation in between your phone and the MOSFET, I'll bet the audio signal will work as the trigger input. If it doesn't, use both ideas together, have the square wave from the opamp trigger the 555 timer.

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