Discussions

Howdy DIYDrones. I'm presently working on a university research project with a few other students integrating a PixArt IR sensor from a Nintendo Wiimote with ArduPlane. I'm using version 2.24 of the codebase but will likely be porting it forward in the next couple of weeks. I'm hoping to get some input from the APM dev team as to whether or not I've got everything sorted out on the aircraft side of things.

What I want to do is collect data from my sensor and send it over Mavlink to my GCS. Unfortunately, I haven't been able to find a discussion by anyone else that's written a fully-integrated sensor payload addition to APM. The closest I've seen is Eric's post on local logging from a humidity sensor. Here's what I've done so far:

• Wrote a sensor driver. Actually, I took the great work done by the Wiibrew community and especially the Arduino PVision library from Steve Hobley and added some features and generally adapted it to my needs. The big change I made is implementing on-the-fly sensor sensitivity settings changes. I've tested and debugged it on the ground in test software (not the APM codebase.)
• Included the sensor driver library in the ArduPilotMega.pde Libraries section.
• Added the sensor data object declaration to ArduPilotMega.pde Sensors section. The constructor is set up to fully initialize the sensor so no further code is required before data can be read.
• Added the sensor data object read/update command to the medium loop in the same case as the GPS. I don't need updates very often and wasn't sure which of these has the least overhead and could take the additional overhead of the sensor update command. It's a pretty straightforward I2C transaction of 10 bytes so the additional latency should be low.
• Wrote a new .xml file defining the Mavlink messages I want to use to get data from the sensor and send new sensitivity settings from the ground station and included it in ardupilotmega.xml. They're defined as <message>.
• Used mavgen to autocode the C helper functions for the entire project, then overwrote the relevant files in libraries/GCS_Mavlink/include. Since I'm on 2.24 I used Mavlink protocol version 0.9 instead of 1.0, but I should be able to change that to 1.0 without messing with the .xml in the future?
• Added send_message commands with my Mavlink helper names to the available streamRateExtra3 stream in GCS_Mavlink.pde.
• Added a case to handleMessage in GCS_Mavlink.pde which sets the sensitivity settings on the sensor when it receives the set sensitivity message.
• Added cases for each message to mavlink_try_send_message in ArduPilotMega/Mavlink_Common.h.
• Incremented the MAX_DEFERRED_MESSAGES value in Mavlink_Common.h by the number of messages I added.
• My team wrote a parser and UI widget for HK GCS using the new message definitions, but maintaining it is turning out to be a royal pain. We're in the middle of porting it over to QGroundControl.

So all of the above compiles but I don't really have any way of testing it until the ground station guys finish. I'm just wondering if I missed anything so we can avoid some headaches later on. Also, what's the preferred method of maintaining stuff like this (version control, diff patches?)