🚀 go-pugleaf

In article <921@PSUECLB>, mrb@psueclb.BITNET writes:
> 
> Hi ---
> 
> I am interested in obtaining the protocol used for signalling between the
> IR handheld remote control of a Scientific-Atlanta Homesat 900 satellite
> receiver, and the receiver itself.  While this seems pretty specific, any
> information on similar home-entertainment IR remote control schemes would
> also prove useful.

I recently built a handheld controller that can be programmed to emulate
the infra-red remote controls for a number of different devices.  In
general, it is not necessary to understand the details of the transmission
formats as my box just "records" the signals and plays them back. 
However, while debugging it I did find it necessary to study the protocol
for one device (my VCR) in detail.  I hope this is useful.

My VCR with infrared remote came from Montgomery Wards, and is
manufactured by Sharp.

The VCR encoding scheme uses pulse position modulation of a carrier.  The 
carrier has a frequency of about 37.73 KHz with a 64% duty cycle.  A logical 
"one"consists of 255 microseconds of carrier on followed by 799 microseconds
of carrier off.  A logical "zero" consists of the same 255 microseconds of
carrier on followed by 1855 microseconds of carrier off.  As a result, it
can be seen that the total time to transmit a string of bits depends on 
the relative number of "ones" and "zeroes."  (These times are based on the
those used by my programmable controller and are only anapproximation 
of the timing actually generated by the remote control.  In practice, 
a significant amount of variation is allowed.)

The actual bit pattern to indicate a function is as follows

- A three bit sync pattern (1, 0, 1)
- 10 data bits indicating the function to be performed
- A pause (no carrier) such that the total time since the start of the
    first sync bit is 50.6 milliseconds.
- Another three bit sync pattern (1, 0, 1)
- 10 data bits that are the logical inverse of the previous 10 data bits

Ten bits is far more than necessary for the limited number of functions
provided.  Presumably, the same scheme is used for more complex remote
control devices.  The functions provided by my remote are:

Stop		1,0,1,1,1,1,1,1,1,1
Play		1,1,0,1,1,1,1,1,1,1
Power on/off	0,1,0,0,1,1,1,1,1,1
TV/VCR		1,1,1,1,0,1,1,1,1,1
Rewind		0,1,1,1,1,1,1,1,1,1
Fast Forward	0,0,1,1,1,1,1,1,1,1
Channel Up	1,0,0,0,1,1,1,1,1,1
Channel Down	0,0,0,0,1,1,1,1,1,1
Record		0,0,1,0,1,1,1,1,1,1
Pause		1,0,0,1,1,1,1,1,1,1
Frame Advance	0,0,0,1,1,1,1,1,1,1

-- 
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