I have finally implemented the protocol. The information from the forum was pretty useful. It gave me a direction to think. I am giving you a brief details of my work, in case somebody needs it.

The work assigned to me was to change the temperature and fan speed. My first step was to build a custom made detector, which was made using TSOP1736 from Vishay. I had connected a resistor divider network, as it appears on www.lirc.org, at the output of detector. The output of the resistor divider was given to mic input of the PC. I used software - 'dictation buddy' for recording the waveforms in the .wav format and the details of the waveform were seen using software - audacity. I had an digital oscilloscope of 50MHz bandwidth to cross verify the same. I was so surprised to find that the waveforms recorded on the PC were easier to interpret. I am giving the protocol as under: -

A complete transmission is a Start Condition followed by 7 bytes(B0 to B6) of tranmission and finally termination condition. There is a time gap and again a start condition is issues followed by 15 bytes( B7 to B21) of tranmission and finally termination condition. The information for temperature and fan speed is contained in B17, B18 and B21. B17 has the temperature state and B18 has the fan state while B21 is the CRC. All the other bytes were fixed and they are: -
B0 - 0x11, B1 - 0xDA, B2 - 0x17, B3 - 0x18, B4 - 0x04, B5 - 0x00, B6 - 0x1E, B7 - 0x11, B8 - 0xDA, B9 - 0x17, B10 - 0x18, B11 - 0x00, B12 - 0x53, B13 - 0x00, B14 - 0x20, B15 - 0x00, B16 - 0x00, B19 - 0x00, B20 - 0x20

The value of B17 representing temperatures from 16 to 32 are: -
16 - 0x0E, 17 - 0x10, 18 - 0x12, 19 - 0x14, 20 - 0x16,
21 - 0x18, 22 - 0x1A, 23 - 0x1C, 24 - 0x1E, 25 - 0x20, 26 - x22, 27 - 0x24, 28 - 0x26, 29 - 0x28, 30 - 0x2A, 31 - 0x2C, 32 - 0x2E

The fan is either fast or slow yielding its two possible values as presented by B18: -
slow(S) - 0x16, fast(F) - 0x36

The CRC information in B21 has been given for all the temperatures, for both fan states as

follows: -
16(S) - 0xD1 and 16(F) - 0xF1, 17(S) - 0xD3 and 17(F) - 0xF3, 18(S) - 0xD5 and 18(F) - 0xF5, 19(S) - 0xD7 and 19(F) - 0xF7, 20(S) - 0xD9 and 20(F) - 0xF9, 21(S) - 0xDB and 21(F) - 0xFB,
22(S) - 0xDD and 22(F) - 0xFD, 23(S) - 0xDF and 23(F) - 0xFF, 24(S) - 0xE1 and 24(F) - 0x01, 25(S) - 0xE3 and 25(F) - 0x03, 26(S) - 0xE5 and 26(F) - 0x05, 27(S) - 0xE7 and 27(F) - 0x07,
28(S) - 0xE9 and 28(F) - 0x09, 29(S) - 0xEB and 29(F) - 0x0B, 30(S) - 0xED and 30(F) - 0x0D, 31(S) - 0xEF and 31(F) - 0x0F, 32(S) - 0xF1 and 32(F) - 0x20

All the bytes should be transmitted with LSB first.

To interpret the waveform following information was used: -

A start bit is 5 millisecond ON and 2 millisecond OFF
A zero is approximately 525 microseconds ON and 525 microseconds OFF.
A 1 is approximately 525 microseconds ON and 1600 microseconds OFF.
A terminating bit is 525 microseconds ON and more than 1600 microseconds OFF.
The time between start and repeated start condition is approx 30 milliseconds.


The temperatures that I successfully switched were 17, 20, 23, 26 and 28. Both the fan speeds

were successfully switched. The carrier frequency of the transmitter was 32.768Khz.

I hope that I have covered all the technical information in brief.

Thanks all