Background • Software Engineering type • Day Job • FeedHenry • Spare Time • Hacking (github.com/jasonmadigan) • iOS Apps • Irish Weather • Matchy • Bit of a Space nerd Monday 19 August 13
Arduino Mega • 4 Hardware Serial Ports • Software Serial ports introduce problems! • Processes GPS data from the MTK3339 • Processes incoming AT commands read from the GSM TC35 modem for sending/receiving SMS • Controls telemetry transmission via RTTY sent via NTX2 Monday 19 August 13
MTK3339 • Low power (20mW) • On-board data logging • Works above 18km • COCOM limits • 1900km/h && > 18000m - turn off • No intercontinental ballistic missiles, please • Actually worked up to 3.7km. Once. Monday 19 August 13
Radiometrix NTX2 • Low power transmitter UHF (10mW) • Free/unlicensed to use at low power in the UK & Ireland* • UKHAS use these since they’re easy to use • Used to transmit RTTY (Radioteletype) telemetry periodically * Table 5 - http://www.comreg.ie/_fileupload/publications/odtr0062r.pdf Monday 19 August 13
Xexun TK102 • Redundancy! • Cheap GPS Tracker with GSM (€30) • Terrible • Doesn’t work when it’s upside down • Randomly stops responding • Has failed to work on two HAB missions • I should probably throw it out. Remind me to throw it out. Monday 19 August 13
Siemens TC35 • GSM module with a serial (RS232) interface • Works with an Arduino • Low(ish) power 120mW while idle, can spike to ~700mW when sending/ receiving SMS Monday 19 August 13
How it all works • Redundant communications system • GSM (via TC35) • SMS processing - I can call or text “where”, and it will text me back its location • UHF (via NTX2) • Transmits periodic RTTY for decoding on the ground (dl-fldigi) • Cheap GPS tracker Monday 19 August 13
Bugs! • There were/are many • My favourite - Arduino serial interupts • Originally using an Uno • 1 hardware serial port (I needed 2) • Software serial ports • I have data, I interrupt • Oh you were transmitting? Sorry about that. Monday 19 August 13
Launch Day • Oh crap the antenna broke • Oh crap the voltage sensor snapped off • Oh crap we forgot to put in the video camera • Oh crap I forgot to close the Helium valve before disconnecting the regulator Monday 19 August 13
Oops • Checked the predictor, started heading north towards Coleraine • “Odd, it’s altitude seems to be stuck at 3.7km” • GPS never regained a lock until it landed • We could hear the Payload via UHF Radio for the whole chase Monday 19 August 13
Silence • Shortly after regaining GSM coverage, the Radio went silent. • TC35 & GPS Tracker still working, so frantically called them • Eventually the main tracker told us its location Monday 19 August 13