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How to remotely trigger any DSLR from a drone using relays, Alexmos 32 and Mavlink

^ That's what we are going for

So, you have your perfectly balanced DSLR or mirrorless gimbal setup and stabilizing, your copter PIDs autotuned and flying great.  Your flight controller is outputting Alexmos serial OR Mavlink to an Alexmos 32 bit gimbal controller.  How do you remotely trigger your DSLR or mirrorless camera from the ground when taking aerial photos with your drone?

Good question.  One with loads of possible solutions, this one is the most efficient for the above scenario. If your setup doesn't match exactly but you're engaging in a similar project, skim through as PWM relay triggers are pretty universal no matter what controllers you are using.

DSLR on drone S1000 relay remote shutter
DSLR on drone S1000 relay remote shutter
DSLR on drone S1000 relay remote shutter
DSLR on drone S1000 relay remote shutter
DSLR on drone S1000 relay remote shutter
DSLR on drone S1000 relay remote shutter
DSLR on drone S1000 relay remote shutter
DSLR on drone S1000 relay remote shutter
DSLR on drone S1000 relay remote shutter

Interfacing with the camera.  The camera on the mount right now is a Nikon- which has a proprietary plug called an MC DC 2- which carries remote focus, trigger and GPS.  A quick check on amazon brings up the bare cable for around £5 same day delivery, OR a longer cable with a hand remote for the same price. Awesome. Don't expect amazing quality but the wire is what we are after, and the more flexible the insulation the better- lest you have to strip the insulation to allow your gimbal to move freely.  The one I've linked above is flexible enough.  Camera buttons are very simple circuits- like those in your car. They rely on a signal voltage being connected to the ground of the device- and that closes a circuit and tell's an IC that a button has been pressed. Armed with that knowledge you know that you can open your camera and apply this relay method to any button for full breakout PWM control. Just remember to bin that warranty card- it won't be any use anymore.

Cut the remote shutter cable with enough slack to allow full movement of the gimbal but try to leave some sticking out of the hand remote so it remains useful for the future.  Relays! Get solid state relays, amperage rating doesn't matter. The lighter the better. I've used ones from DIY Drones before and numerous clones. They should cost between £15 and £20. The ones I used in this build were from Mr-RCworld, a UK company who make their own products and even supply datasheets! Nice work.

We are only interested in the pair of terminals without the red dot- the red dot pair are commoned all the time, the ones without are switched with the relay. Use a multimeter in continuity mode to determine which pins on your connector go to which colour cable- there is NO standard with clone products such as my fancy remote shutter button. Turns out white is ground (obviously?) Yellow is focus and red is shutter release.  Wire as per my picture- I've commoned the single ground wire over to both relays. Remember to strip and tin those wires before clamping into the terminals for a more effective grip and a more reliable build; we aren't Space-X but there's no excuse for shoddy electrical work failing at altitude during a mission.

Now you've got one relay controlling focus and one for shutter release. Depending on how clever (or not) your camera is, even in manual focus mode- you may have to have focus depressed to activate the shutter release. I mapped the focus to a toggle switch on the left shoulder on my TX (see video) so it can be left on while the right shoulder has a momentary switch for shutter release.

alexmos settings for servo relay outputs

Alexmos / Basecam 32 bit GUI setup.  You want to map API_VIRT_CH_x (Where x is your transmitter output channel) to Servos 1-4 that correspond to the free outputs you've allocated to your relays.  In this case I've allocated Servo 1 and 2 to channels 10 and 11 respectively. These are the only settings you need to change. Check your work- one of my relays flashed at me constantly- the PWM signal that the Alexmos board was outputting was only between 9 and 501 - we need more like the full 0-2000 range for positive actuation. First ensure your TXs limits are setup to the maximum, then calibrate in the Alexmos GUI under RC settings. This solved the issue. For more information, check out the Alexmos manual, be sure to read the whole thing otherwise nothing makes sense!

Wrap your wires in cable braid to protect them and keep things looking as tidy as possible- secure the relays, which with their handy screw terminals will now accept wires from any camera's remote shutter cable. Stand back, film a short poor quality youtube video and admire your work. Coffee time.

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