Pixhawk CHDK trigger


The Pixhawk-CHDK trigger will let you use Pixhawk-based drones (like the IRIS+) with a CHDK compatible camera for aerial photography without using a whole mess of duct taped-together UBECs and LED switches and whatnot.

The Pixhawk-CHDK trigger has three input connections in a 0.1" locking header which is compatible with standard servo lead connectors. Power and ground is taken directly from the flight battery (3S or 4S) and the input signal directly from an auxillary output on the Pixhawk. No need for BEC/UBECs or for powering the servo rail on the Pixhawk.

Output to the camera goes directly to the camera's USB port. (Using a locking 2-pin 0.1" header.)


There is also a mini-USB connector for configuring the Pixhawk-CHDK trigger. Configuration is done by connecting the Pixhawk-CHDK trigger to a Mac OS X, Windows or Linux computer and opening a terminal connection (using screen or PuTTY or your terminal application of choice) to the device.

Using a simple command-line interface, a number of intervals (up to 20) can be configured. An interval is simply a definition of an input PWM range and corresponding output pulse length. This will allow the Pixhawk-CHDK to work with all CHDK scripts that use the USB remote control input for control, regardless of how many different commands the script supports.

So if we want the CHDK to receive a 50 ms pulse when the RC signal is between 1800 and 2000 µs, the command would be add 1800,2000,50.

Everything is stored in non-volatile RAM (flash) and the interface currently supports the following commands:

  • help – shows available commands
  • list – shows all defined ranges
  • delete – removes a range
  • add – adds a range
  • show – shows all or a specific settings parameter
  • set – modifies a settings parameter
  • pulse – sends an output pulse of the specified length for testing CHDK scripts
  • isp – enters ISP mode for flashing new firmware

Want one?

Everything is open source and open hardware; all schematics, board files and firmware will be made available shortly along with BOM and assembly instructions.

4 comments on "Pixhawk CHDK trigger"
LeonD says:

Sign me up, looks great!

Larry Field says:

Sign me up, looks great!

dave says:

Sign me up

Peter Stapleton says:

Being a semi retired electronic engineer I was about to design and build basically what you have done although using an Arduino uno and with pulses specific for my Canon 260 What you have done is more versatile and looks great. If they become available I would be interested in getting one. I do aerial mapping with my drones and currently use a bec for the 5v rail and a cable connected to an output configured on the Pixhawk as a relay (Camera Trigger). Are you able to confirm that with a pwm output from the pixhawk and the required usb pulse width generation the mission planner survey tools will generate internal waypoints for triggering in addition to still allowing for camera control using do_set_pwm in the mission.
Regards, Peter

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