Can a Canon EOS 5D Mark II hot shoe trigger my own device when the shutter fires?
Asked 4/24/2013
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I want to connect a custom device to a Canon EOS 5D Mark II and detect when the camera fires so the device can record during the exposure. Can the camera provide a trigger signal through the hot shoe, or does the hot shoe simply act as a switch between the center contact and the shoe ground? If I use the hot shoe this way, do I need to supply my own voltage, and what trigger voltage is considered safe on a Canon body?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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The circuit will connect the shoe mount to the center pin to fire. It sounds like up to 6 volts is what Canon asks for, but it can apparently vary a lot depending on the flash. Other pins may contain other signals, but that portion is proprietary in most cases so you'd probably want to use the circuit completion and provide your own low voltage signal. The voltage is normally provided by the flash itself since it has to be the appropriate voltage for the flash's triggering circuitry. The camera only acts as a switch.
Originally by user11392. Source · Licensed CC BY-SA 4.0
user11392
13y ago
0
Generated from our catalog & community — verify before relying on it.
Yes — for the basic flash trigger, the camera hot shoe acts like a switch. When the camera fires the flash, it connects the center contact to the shoe ground/mount. In normal use, the flash supplies the trigger voltage and the camera simply closes the circuit.
So for a custom device, you would typically provide your own low-voltage sensing circuit and detect that contact closure rather than expecting the camera to output a voltage by itself.
On Canon bodies, a commonly cited safe trigger voltage is up to about 6V on the main trigger contact. Since the other hot-shoe pins carry proprietary communication, the safe/simple approach is to ignore them and only use the center pin plus ground.
In short: use the hot shoe as a contact closure, supply your own low-voltage signal if needed, and keep trigger voltage low (around 6V or less to be safe).
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