Pixhawk Camera Trigger Cable - Relay Method


Out dated - Use Servo signal method.


Pixhawk based UAVs can automatically take pictures at a set distance using GPS distances or points. In order to do so you must configure the Pixhawk, Install CHDK on a compatible Canon Powershot camera, install KAP UAV Exposure Control Script, and connect the Pixhawk to the camera with a trigger cable.

Configure the Pixhawk

  1. Open Mission Planner and connect to your Pixhawk.
  2. Select Config/Tuning > Full Parameter List and set the following:
  • RELAY_PIN (50-55) Use the image below to pick an open relay pin for the camera trigger cable.
  1. Press the Write Params button.

Install CHDK on a Canon Powershot camera.

CHDK is free, non permanent software that runs in addition to the firmware on certain Canon cameras. Among other things, it allows you to run scripts that can remotely trigger the camera by sending a 5 volt pulse through a USB cable. It is installed on the camera's SD memory card, so no modifications are made to the camera. The easiest way to install CHDK is by using a program called Stick.

  1. Downlaod Stick.
  2. Follow Stick's instructions to install CHDK on your camera's SD memory card.
  3. Follow the CHDK instructions for loading and using CHDK on your camera.

Install and configure KAP UAV Exposure Control Script on your camera

The KAP Exposure Control Lua script runs under CHDK and automatically controls shutter speed, aperture, ND filter, and ISO settings so as to maintain the fast shutter speeds needed in aerial photography. Additionally it allows you to trigger your camera by sending a 5 volt pulse to the camera's usb port. Do the following to install and configure KAP UAV Exposure Control Script:

  1. Download KAP UAV Exposure Control Script. (kap_uav.lua)
  2. Copy kap_uav.lua into your (SD Card:)\CHDK\SCRIPTS.
  3. Lock your SD card, insert it into your camera, and turn your camera on.
  4. Press the Play button.
  5. Press the FUNC SET button to select the Script Menu.
  6. Press the FUNC SET button to Load Script from File.
  7. Select KAP_UAV.LUA using the Outer button and FUNC SET button.
  8. Set Shot Interval (sec) to Fast
  9. .
  10. Use the Outer button to move down the list until you select USB Shot Control? Use the FUNC SET button to rotate options until OneShot is highlighted. Press the Menu button to exit the KAP_UAV.lua options.
  11. Half Press the shutter to start KAP_UAV.lua.
  12. Your camera is ready when you see Waiting on USB.
  13. The default exposure values should work on a sunny day. If necessary, use the KAP UAV Exposure Control Script documentation to modify exposure values.

Connect the camera trigger cable

A special Pixhawk camera cable is required to trigger your Canon camera. As your UAV flies past predetermined points, the Pixhawk will provide a pulse to the Aux Out pin specified by the RELAY_PIN parameter.


Do the following to verify your system is working:

  1. Connect the servo style connector from Pixhawk camera cable the to AUX OUT 5 on the back of your Pixhawk. Note! the Pixhawk does not provide power to the AUX OUT pins. You must provide 5 volts to the AUX OUT pins by plugging in an ESC with a Battery Eliminator Circuit (BEC) or a Universal Battery Eliminator Circuit (UBEC) into any open pin set. Read here to determine if you need a BEC.
  2. Connect the mini USB connector from the Pixhawk camera cable to the USB port on your Canon camera.
  3. Turn on your camera with CHDK and start the kap_uav.lua script so that waiting on USB signal is displayed.
  4. Start Mission Planner, Connect to your Pixhawk and go to the Flight Data screen.
  5. Right-click on the map and select Trigger Camera NOW. If everything is setup correctly your Pixhawk will trigger the Canon camera to take a picture and is capable of triggering pictures using GPS distance.

Hint: Make sure Review is turned off your Canon camera's menu. Canon camera > Menu button> Review "off".