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→Data format for firmware V2.4 (recent production units)
* speed is a two-byte information, little-endian. It represents the speed, in 64th of RPM (aka value in RPM represented in fixed point, with 6 bits used for the decimal part).
* Data 0 to Data 3 are the 4 readings. Each one is 4 bytes long, and organized as follows :
<br /> byte 0 : Distance 7:0 byte 1 : “invalid data” flag : “strength warning” flag byte 2 : Signal Strength 7:0 byte 3 : Signal Strength 15:8
As chenglung points out, the distance information is in mm, and coded on 14 bits. This puts the tests made by Sparkfun in a room of around 3.3m x 3.9m (11ft x 13 ft ?), which seems reasonable.
The algorithm is as follows, provided that `data` is the list of the 20 first bytes, in the same order they arrived in.
<br />
def checksum(data):