I have a Canon T5 with a 2.5 mm shutter release port. I would like to be able to trigger the shutter from an audio output jack on a PC. Would it be possible to trigger the shutter release using a "beep" noise sent from the computer?
Since the other answers suggesting using an interface such as triggertrap don't address the specific question to your satisfaction: No, this is very, very unlikely to work. Despite the plugs being similar, they serve very different purposes. The camera release is basically an open circuit with a voltage potential (measured at 3v on mine) waiting to be closed by a switch, either mechanical (a simple button or slide switch) or electronic (as in the case of audio triggers, intervalometers, etc). An audio output is designed to present a fluctuating voltage across a load, not to close a circuit.
Given that there's a certain threshold resistance below which the camera will decide that its circuit has been "closed", and that audio outputs of the sort that you describe may very well present a resistance in that range, there's a reasonably good chance that simply plugging the two together will trigger the release.
Even if the shutter doesn't release just from plugging the two together, playing a sound is unlikely to do any triggering, since it doesn't do anything to close the circuit. Your audio output may even have a capacitor inline blocking the DC from the camera (and if it doesn't, it might not be very happy to have the voltage applied to it). Sorry! You can probably find some DIY interface projects out there, if you just can't resist the mad science. (See Chris H's answer for an example of just how simple of an interface you might be able to use.)
Yes, you can but you need an opto-isolator
I've built a few cable releases for Canons, from a simple pushbutton to a USB (via a USB-RS232 dongle) trigger, to one triggered off a burglar alarm PIR sensor (for use as a camera trap).
It won't be simple to trigger it off a sound card. If you can get enough voltage you might be able to modify my USB trigger circuit - you'd need to rectify the audio output before feeding the opto-isolator(s).
The circuit (and code to talk to it) are freely available on my github if you want to use them as a starting point.
I don't know what voltage (and current) a typical sound card can drive - but with clever design of the rectifier circuit it should be possible. With a further power source it would be easy - but I assume you want to avoid that (you could steal enough power at 5V from a USB port, or even a serial port)
I've just done it. I used the circuit on my github, but connected an audio channel directly to the LED positive pin of the opto-isolator (no series resistor), using the LED as its own recitifer. With a 3-ish V peak-to-peak signal and a low frequency (about a 20Hz sine wave) it triggered. I'm not sure whether it wasn't 100% reliable or whether I was having trouble holding everything together (I didn't have the right connectors). I have a couple of ideas for improving things (involving Schottky diodes such as the 1N5817, capacitors, and possibly both audio channels in anti-phase), but I don't have the parts to test.
Here's the circuit I used this evening. You really should have a series resistor between the LED though I didn't while testing:
The shutter release ports on Canon cameras as well as pretty much any other DSLR (there is at least one notable exception: Panasonic/Lumix) are very simple. The only difference is the shape of the connector selected. All you need is continuity to trigger them.
If the camera is in Bulb mode the length the continuity is maintained will determine the length of the exposure. If the Tv is set by the camera the circuit need only to be closed for a duration long enough for the camera to recognize it.
The defunct TriggerTrap app used the headphone jacks of phones to trigger cameras via a dongle that translated the tone from the phone to the continuity needed by the remote circuit connected to the camera. The dongle was acting as a relay. When it detected an audio signal from the phone it closed the circuit connected to the camera.
Here's a link that shows the pinouts for most recent DSLRs.
They both use jack as the plug and socket and this is the only thing they have in common at all.
See Caleb's link to my, sligthly different, question
In the remote control there are two simple switches, one closes the circuit of AF and the second one the circuit for shutter release.
There was a cellphone app called TriggerTrap (its since gone under) that used the headphone jack of a phone to control a camera of your choice so I think there is a solution for it if using a relay.
If you are using a computer instead of a device like a phone. You can use the EOS Software to control your camera via USB cord and you can get really long USB cords. If the EOS software doesn't do exactly what you are looking to do and you have some development skills, look into the Canon SDK. Some information can be found at Canon.
I use a USB micro to USB micro with another app that I have purchased with my phone that is designed for Canon cameras. It allow you to control your Canon Camera with many different functionalities. More details about the app can be found at How to programme EOS utility to take n number of shots?
I use a Canon 7Dii and T4i. It also worked on a T2i before I sold off the T2i. I did not design the app but only came across it when I was looking to try out time-lapse.
DSLR Controller (BETA) - it costs about $7.99 (CAD or USD, I forget)
Remote Release - A Test app before purchasing the DSLR Controller