Hi all. I purchased a new Runcam 2 for my Flamewheel 450 quad only to discover that there is no way to run a remote shutter trigger. Nothing came up on forum searches so I came up with one myself. I'm running a Pixhawk APM and use Aux5 in Relay mode for the camera trigger source. I opened up the Runcam and took some measurements on the shutter switch. It's a PCB mounted switch with four solder legs. The two legs closest to the rear of the camera are at ground potential. The two legs closest to the front of the camera are normally open and sit at 3 volts. When you press the switch it closes and pulls the 3 volt line to ground. Simple enough. I carefully soldered two small wires, one to the ground and one to the signal contacts. Then I drilled two very small holes (.040") in the side of the top case just ahead of the USB port and ran the wires out, using a little super glue to secure them.
Next, I needed an open collector inverter circuit to convert the Pixhawk relay output (zero to 3.7 volt transition) to a high-to-low pull down for the camera. This was accomplished simply with a 2n3904 (ore equivalent) transistor with a 2.2k ohm series resistor to the base, emitter grounded, and open collector connected to the camera signal line.
I programmed the Pixhawk for a 0.5 second camera trigger and presto, remote triggering of the Runcam2. I can now easily turn a video recording on or off in flight using the channel 7 Camera Trigger setting, or fire a still photo from the Do_Digicam_Control or Do_Set_Cam_Trig_Dist mission commands.
It works great. Let me know if you have any questions about implementation. You have to be very carefully soldering inside the Runcam. Space is limited and there is high potential for a solder bridge somewhere unwanted.