An experiment to transmit JPEG images live during the flight over a low power radio link, by Philip Heron.

To transmit small (320×240, ~5kB) JPEG images over an 8-bit RTTY signal at 300 baud, with a transfer time of between 2 and 5 minutes depending on the complexity of the image.

The current module consists of:

• ATmega644P clocked at 7.3728MHz
• NTX2 radio module @ 434.075MHz
• C328-7640 JPEG Camera Module (SparkFun)
  • Takes fairly good images up to 640×480, but because of the slow data link it will only be used at 320×240. All of the JPEG compression is done on-board the camera so is ideal for using with a lower power microcontroller, which only needs to package and transmit the data.

• Reed-solomon encoder / decoder. See: rs8encode
• Modified version of dl-fldigi http://github.com/jamescoxon/dl-fldigi

• JPEG is not a good choice of format as missing blocks will likely cause unrecoverable errors in the rest of the image.
• RTTY is not the best mode for transmitting the data, but is incredibly easy to implement with the NTX2 radio module.
• A method of re-transmitting lost blocks - requires an uplink of some kind and the blocks to be stored.
• Distributed listener - each client uploading received blocks to a server.

The HADIE module flew on the 16th April 2010 as part of ProjectCirrus, reaching over 30km altitude. The module and camera worked throughout the flight, transmitting the position and image data until the harder than expected landing destroyed the board. The 10mw signal from the NTX2 was picked up as far away as Yarm in England, 366km to the east.

The payload was spinning for most of the flight causing the signal to fade in and out. Because of this about 5% of image blocks where lost which unfortunately resulted in most of the images being incomplete. Once a block is lost, any subsequent data received for that image is also lost.

A second flight is planned for the 10th October. It will largely be a repeat of the previous launch but with the improved reception code and hopefully more complete images. A few others changes:

• Interrupt driven RTTY code with a single pin and two resistors. (3.3v → 330 ohm → NTX2 tx pin ← 2.2k ohm ← rtty output pin)
• The new robust image format, a lost packet will not ruin the rest of the image.
• A network of listeners should hopefully reduce the chances of a lost packet.
• Quarter-wave dipole antenna, mounted so that the module doesn't take the full force of the landing.
• Canon A560 camera with CHDK and script to take regular images.

The flight code for Hadie-2 is avaialble here: http://github.com/fsphil/hadie

Despite the damage the board sustained in the last flight all of the components survived so the same UART camera and radio module will be flown on this flight.