I'm trying to identify the following modulation scheme being used to transmit a infrared code. It looks like manchester, but there's some gaps where there's no transitions.

The code being transmitted is

in hex = 621da4

in bin = 01100010 / 00011101 / 10100100

there may be a check byte at the end too. I've attached pictures of the beginning of the code, the end of it, and a zoomed out capture of the whole thing.

any help immensely appreciated!

beginning the beginning

end the end

zoomed out zoomed out

  • \$\begingroup\$ What is the timebase of the scope? What device produces these? How do you know the data being transmitted without understanding the protocol? It can't be bi-phase (manchester) coded as there are pauses and pulses longer than 2 periods, which also rules out the common RC-5 remote control protocol. It isn't Sony's SIRC or the NEC protocol either, as pulse length modulation is clearly not being used. It's not the plain binary data either. Maybe this can help: vishay.com/docs/80071/dataform.pdf \$\endgroup\$ – jms Feb 21 '16 at 13:57
  • \$\begingroup\$ Do you have an Arduino and an infrered receiver lying around ? If so load one of the Demos of the IRLib library and it might tell you what coding is used. \$\endgroup\$ – Bimpelrekkie Feb 21 '16 at 14:46
  • \$\begingroup\$ Hi. The period for the whole signal is 1.5ms, and the width of the smallest pulse is 25us.. The graph period is 50us. Arduino it lib won't work as it's too fast. It isn't consumer ir. The device is an identification transponder \$\endgroup\$ – user3780104 Feb 21 '16 at 15:27
  • \$\begingroup\$ I see at least 56 'pulse periods' between the first an last 'pulse blocks' on your graph. Are you sure that it's transmitting those 24 bits of data you listed in a non-encrypted format? It would be really eash for me to believe that I'm looking at a crypto hash output there. \$\endgroup\$ – Robherc KV5ROB Feb 21 '16 at 16:56

I am pretty sure that the IR carrier is just on-off keyed with the output of an UART.


It's 8-bit asynchronous serial, probably at 38400 baud, with a single stop bit. There are 6 bytes of data in a transmission. It can't be 7-bit serial with a parity bit, as the last bit matches up with neiter odd nor even parity.

The data being transmitted is
01101111 00111011 11000010 10000000 01101000 00010010 AKA 6F 3B C2 80 68 12

No idea what it means. I would have to know what specific device is being reverse-engineered to proceed further. The endianess might be different from what you expect and there is probably either an an error correcting code or a checksum.

  • \$\begingroup\$ nice one thanks. There's a 7.392mhz crystal on the board too so serial makes sense. just need to figure out why it doesn't match the code! :-) \$\endgroup\$ – user3780104 Feb 21 '16 at 18:17

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