I’ve been doing some further tests on my payload VAYU whilst I wait for the new PCBs to be fabricated. This is the prototype built from Chris Stubb’s CHEAPO PCB with an added boost regulator. I wanted to see how long it would run for on a pair of almost new Lithium AAs. The boost regulator is meant to be able to take 1.5V and boost it to 3.3V after the small resistor modification. I was surprised to find that with two AAs in parallel it wouldn’t fire up the board. I re-tried it from PSU and it was fine. I can only assume it’s lack of current, although the batteries are supposed to be able to peak 1A.

My solution was to connect the batteries in series and feed the boost regulator with just under 3v. The board happily works at this level. Since I was going to send two AAs up with the payload anyway, it doesn’t matter with regards to weight. The only impact may be performance. I ran the board for a while to see how stable it was and it performed adequately. I then put it in my freezer. It was very interesting to see how far the frequency drifted and how fast it went on it’s journey down to -7deg (internal AVR reading). I left it there for around 15mins and it worked fine. I then placed it on the window sill and left it for 4hrs. The frequency stabilised after a few minutes and it ran quite happily. By the end of the test, the batteries still read at 2.83V.

Testing the VAYU Prototype in the freezer.

Another thing I did was re-program the AVR to send out this website’s address interleaved with the telemetry. Before flying, I’ll have to remove the _TEST in the callsign. This is a pretty easy process which I will document at some stage.