The Pixhawk-CHDK trigger is coming along nicely. The prototype is done and the firmware is almost done.
The firmware is actually very simple. I'm using 32 bit timers for both measuring incoming RC PWM signal for for outputting 5 V pulses of specific lengths and all the USB CDC functionality is copied-and-pasted from a previous project. The most complex part is actually for command-line interface (or "CLI") parser.
To configure the device you plug into your computer using a mini-USB cable and then connect using Telnet, screen or other terminal application.
The command set is pretty simple and supports the following commands:
list -- shows all defined intervals add 1000,1200,85 -- adds a new interval delete 1 -- removes entry 1 change 1=1000,1300,85 -- changes entry 1 pulse 50 -- sends an output pulse of 50 ms show -- shows all settings parameters show <setting> -- shows the value of a single parameter set <settings>=<value> -- changes the specified settings parameter help -- shows available commands ? -- same as "help"
No need to "save" or similar. Everything is stored in EEPROM as soon as it is entered.
The PCB design is also almost done. I just need to check it a couple of times (time well spent, trust me) and verify footprints (likewise time well spent). The size is 5 x 2 cm and even though I probably could squeeze it down some more, I think I'll keep the current size seeing as how I'll be hand-soldering some of the parts and applying solder paste and components all by hand.
Here's a rendering (from the excellent 3D Gerber Viewer from Mayhew Labs: