Sometimes, we do reverse engineering for fun.                 

1.3 IR remote protocol (codes) for Turbo Hawk helicopter, 'PROTOCOL'.

  This IR  independently controls three DC motors. 2 - one direction w/PWM, and one, with bi-directional PWM.  Despite the fact that it looks complicated, it works no more complicated than IR remote control for 'Battle Tank'. We will not disassemble remote and look what is "under the hood". Instead, we will connect a simple 'logic analyzer' to IR sensor of another helicopter and see what happens during transmission.

  IR transmission operates on a standard 38 kHz sub-carrier, transmits only when  "throttle" (left handle) a 1/4 up or more. After releasing "throttle" (to '0'), it transmits three more codes and disables IR transmission. Interval between packages always 150mS.

  If we stretch the code in time, for example when you released the throttle, we will see the following ('high level' - no carrier, 'low' -  38 kHz is ON). It shows width / period of pulses inside the package.

  The coding of "zeros" and "ones" is brilliant, because it is very simple. After the start pulse, any transition (Lo to Hi, and Hi to Lo) means the beginning of a next bit. If it is followed by a long pulse, then it is “1”, if pulse is short, then “0”. It's very easy to read. If you understood everything correctly, then you will count 40 bits on the picture above.

  You can decode manually. It does not take much time.

  Finally, if you rewrite everything in binary, it starts to make sense.
  The last byte is checksum (last 5 bits, only). I do not have time to determine the algorithm for its calculation (spent some time and gave up). If you can do this, please let me know. Thank you!


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11.12.2019 SKootS

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