Pixhawk Relay - How to drive a 5V reed relay to trigger a camera - Discussions

Hi,

I'm using APM Copter 3.2 and I'm trying to add trigger as well as mode change capabilities to my GoPro camera. I'm currently exploring to hack the wifi remote that comes with the Hero3+ black so that I can control both the shutter as well as the mode change switch remotely.

The Wifi remote has to push buttons which need to be bridged so I was thinking of using the relay function of Pixhawk to bridge those on command.

In essence I have 2 questions:

is it possible to control more than 1 relay pin via the RC link? I found only descriptions on how to switch the primary relay so far
I would need some help with the driver circuit as outlined below

Driver Circuit:

As the Pixhawk provides 3.3V only a circuit is required to drive a 3.3v relay instead.

I found a few examples here in the forum but most are for CHDK applications and the one I found for relays - see below - works in the opposite direction I would need it to function (the relay opens when the camera trigger is pushed). I was thinking of simply removing the 2nd MOSFET to drive the reed relay directly but I'm not certain whether this has negative effects (e.g. overloads the 5V BEC).

Any advice is highly appreciated. Thanks !

Replies

Andre K. June 28, 2015 at 2:02am

Anything involving a relay is a ridiculous overkill, you may use an optocoupler and one or two resistors at most.
- naish > Andre K. June 28, 2015 at 2:15am
  
  What will be the difference in using an optocoupler instead of an SSR? ( and SSR is essentially an optocoupler with a mosfet inside ). Plus I don't think you only need and optoupler and one or two resistor.. you will need more than that to isolate the gopro circuit to create a clean and isolated switch for the gopro remote.
naish June 27, 2015 at 11:54pm

Design 2 will be the most suited.. a small realy should't use more than 150mha so there is no risk on overloading the BEC.

My suggestion will be to use a more simple approach.. just use a SSR ( solid state relay). you will be able to drive it form the 3.3V coming form the pixhawk. You will only need one SSR and one resistor.
- IdefixRC > naish June 29, 2015 at 11:40pm
  
  Thanks for the reply.
  
  Do you have a suggestion on the SSR type to use? Why would a resistor be required?
  
  Thanks !
  - naish > IdefixRC June 30, 2015 at 1:01am
    
    It's best that you look at what is available at any electronics shop near you, as will be cheaper.
    
    As reference I used this one in few of my designs, and it's fine. ( http://au.mouser.com/ProductDetail/Avago-Technologies/ASSR-1219-001...)
    
    A resistor normally is used to limit the current pulled out of the pin, in this case you won't probably need it. If you use the APM 2.5 then a ~ 348 resistor is needed.
    - IdefixRC > naish July 1, 2015 at 8:17pm
      
      Thanks a lot.
      
      Final question :-) is there a way to control 2 relays via the remote?
      I believe Copter 3.2 only has the option to control the first relay via CH7 or 8, correct?

This reply was deleted.