Live sen on webcam
I tried a few webcams and settled on the Logitech C270 which is reasonable quality, light and cheap (in case the payload goes missing! I tried several webcam imaging programs and found fswebcam to be the best (worked without fiddling, yet had enough options to tailor the picture taking).Remember that the radio system has low bandwidth and with a typical flight lasting 2 hours or so we don’t have time to send large images, so there’s no point using the very best webcam and the highest resolution.A simple shell script took a photo every 30 seconds, saving them on the SD card so that the tracker program could choose the “best” image (largest jpeg! Each chosen image is then converted to the form for download (split into blocks each with FEC) before being sent 1 block at a time.I interspersed the image data with telemetry – 4 image packets for each telemetry packet).
The job of the tracker is to read the location from the GPS receiver, possibly also read some sensors, and then format and send a telemetry sentence to the ground over a low power radio link.The usual technique with the NTX2 is to send the ‘1’ and ‘0’ values in RTTY by waggling a general purpose I/O pin up and down at the correct rate. However the Pi runs a non-real-time operating system, so I could not rely on accurate timing especially if the operating system is busy taking a photo from the webcam.There are other options but I opted for the simplest one – connect the NTX2 to the serial port.This is a lot of heat to get rid of a payload (which is insulated because you don’t want it to get too cold either because that can affect other parts).I had some switched mode regulators ordered but they didn’t arrive in time for my flight, so it went up with the linear regulator. This is easy when you’re programming a bare-metal AVR or PIC – just use a delay routine or, as in my trackers, a timer interrupt.