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Feb 12, 2009, 03:47 AM
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Sonar & XBee dreams

$parkfun took 2 days to process the more sonar transducer order. Meanwhile, tied a 1000:1 amplifier to the EZ-1 transducer & recorded the pulses. Take a look. Unfortunately, this oscilloscope removes DC offset & only samples 96khz so the waveform is pretty worthless. It's just enough to show sonar would probably work with just a simple amplifier instead of a horrific analog circuit.

So if U want the most bulletproof communication, U need adaptive frequency hopping. 2.4Ghz Xbees don't do adaptive frequency hopping. U would need to use API mode to change frequencies fast enough. The algorithm would work like this:

Constantly hop between all frequencies to map out what frequencies R good.

The ground station maps out the best frequencies by counting errors & weighs packets towards those frequencies.

The copter starts by listening to 1 frequency & the ground station starts by hopping the current pattern.

Every packet from the ground station contains the current hopping pattern, the start time of the hopping pattern, & the current time.

The ground station changes hopping patterns at certain intervals. It broadcasts the new hopping pattern & new start time a certain time ahead of schedule so the copter can update.

To change patterns, the ground station needs to receive at least 1 packet in response to the current pattern.

In case the copter doesn't get it in time, half of the time slots are the same as the previous pattern & these slots cover all the frequencies. It takes 2 new patterns to replace the pattern completely.
Last edited by Jack Crossfire; Feb 12, 2009 at 05:00 AM.
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