HAB (High Altitude Ballooning) is a growing hobby where enthusiasts use
standard weather balloons to put small payloads typically 100g-1kg into
“near space” at altitudes of around 30km or so, carrying a tracking
device (so the balloon position is known throughout the flight) and
usually some sensors (temperature, pressure etc) and often a video or
stills camera storing to an SD card for later retrieval. 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. Flights only happen once the
predicted path is known to be safe (avoiding airports and densely
populated areas for example) and permission has been gained from (in the
UK) the CAA. Here the tracking system uses the 70cm radio band (around
434MHz) using RTTY to send the telemetry down to a number of ground
stations run by other enthusiasts. Telemetry from all receivers is sent
to a central server that then drives a live map which can be viewed by
anyone with an internet connection. The system works extremely well and
has been used to track payloads at distances of 800km and more even
though the transmitter is limited by UK law to 10mW ERP.
In early May I received my first Raspberry Pi computer, and having flown several high altitude balloons before I thought about using one as a flight computer. In almost all of my previous flights I used Arduino Mini Pro boards, and these are ideal – tiny, weigh almost nothing, simple and need very little power. I looked at the Pi and saw none of these desirable features! What I did see though was a USB port offering quick, easy and inexpensive access to a webcam, meaning that for the first time I could have live images (SSDV) sent down by my payload – something that hasn’t been done very often.
“Near Space” is a fairly hostile environment – less than 1% atmosphere, temperatures down to -50C or so – and if anything goes wrong it’s likely to stay wrong. The radio link is one-way so there’s no chance of remotely doing a “sudo reboot” let alone powering off then on again! Descent can be violent, as can the landing, so even things like SD card sockets can represent a potential failure mode. The Pi is a step up in complexity from the usual boards we use, that have no SD cards, or USB, or even an operating system, so the extra power and capability does come at a price, and the first one is an increase in the power requirement from around 60mA to over 500mA, and that of course means much higher power dissipation. People often worry about the low temperatures in near space, but when your payload is generating a few watts of power that is not likely to be a problem! I was much more concerned with how hot it was going to get inside the payload, so I added some heatsinks to the Pi:
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PIE1 – Raspberry Pi Sends Live Images from Near Space |
In early May I received my first Raspberry Pi computer, and having flown several high altitude balloons before I thought about using one as a flight computer. In almost all of my previous flights I used Arduino Mini Pro boards, and these are ideal – tiny, weigh almost nothing, simple and need very little power. I looked at the Pi and saw none of these desirable features! What I did see though was a USB port offering quick, easy and inexpensive access to a webcam, meaning that for the first time I could have live images (SSDV) sent down by my payload – something that hasn’t been done very often.
“Near Space” is a fairly hostile environment – less than 1% atmosphere, temperatures down to -50C or so – and if anything goes wrong it’s likely to stay wrong. The radio link is one-way so there’s no chance of remotely doing a “sudo reboot” let alone powering off then on again! Descent can be violent, as can the landing, so even things like SD card sockets can represent a potential failure mode. The Pi is a step up in complexity from the usual boards we use, that have no SD cards, or USB, or even an operating system, so the extra power and capability does come at a price, and the first one is an increase in the power requirement from around 60mA to over 500mA, and that of course means much higher power dissipation. People often worry about the low temperatures in near space, but when your payload is generating a few watts of power that is not likely to be a problem! I was much more concerned with how hot it was going to get inside the payload, so I added some heatsinks to the Pi:
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