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Mar 03, 2007, 07:28 AM
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Airtronics terrorism

It took a really really really long time to get telemetry from the ground board to the copter board. The mane problem was a change in plan. Decided to maximize the data rate in the hope of some day sending all the flight controls through the autopilot board, using custom modulation.

So the Airtronics woke up on 3/1/07 emitting a completely different modulation than it did on 2/27/07. Instead of closely spaced pulses for high voltage, it emitted a single pulse at the beginning of every high voltage and no more until the next low voltage.

The behavior of 2/26/07 returned after momentarily changing to the behavior on 2/27/07. The only explanation is either the connection on 2/27/07 was somehow defective or there was interference.

If the pulses are too close together, no pulses are emitted at all.

The duration of a single pulse depends on the duration of the neighboring pulses.

The gap between rising edges of pulses is reproduced perfectly at the receiver.

So the gaps between rising edges would be used to transfer information. To defeat the minimum gap requirement, the gaps would have 16 possible lengths corresponding to 4 bits. Tokenized data U might say.

Broadcasting tokenized data across the dumpy apartment, the Airtronics beamed a nihilistic 3000 bits/sec over its 20khz band including CRC & start code. 10 times faster than the earliest Commodore 64 modems.

On the Gumstix console, from the great beyond, comes an autopilot disable code, but that code could literally be anything. It's like having 16 more channels.

> status=0x00 PWM=191 274 2678 1620
> status=0x02 PWM=143 21 1545 125 radio=0xea8a
> status=0x00 PWM=110 21 2086 825
> status=0x02 PWM=19 21 2237 1003 radio=0xea8a
> status=0x80 PWM=6832 107 1377 247
> status=0x02 PWM=19 3488 1889 454 radio=0xea8a
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