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Issue #201 April 2007
ATir Keyboard Interface
by Steven Savage
Start | System Overview | Keyboard | IR Remote Operation | ATir Hardware | Operation | Nice Solution | Sources & PDF
IR Remote Operation
The infrared remote used for this project transmits a 32-bit packet consisting
of a 16-bit address field, an 8-bit command field, and an 8-bit command
complemented field for error detection. The IR signal is modulated by
the IR remote at approximately 38 kHz. Other modulation frequency receivers
are available in the Sharp GP1UM27XK series from 36 to 40 kHz. With no
signal, the device outputs a high value and it will drive the input low
with the presence of a modulated IR signal. For the remote control, a
logical 1 is represented by a short pulse of approximately 540 µs. A logical
0 is represented by a long pulse of 1,640 µs, with a 570-µs delay between
pulses. Most of the discrete components used in this project comprise
the low-pass filter recommended in the Sharp GP1UM27XK datasheet.
The ATir was designed to support a variety of remote controls by reading remote control commands at run time and not relying on particular commands from a particular remote. The remote used was a surplus unit from All Electronics (a TEAC model RC505), but other remote controls could also be made to work. Although the 16-bit address field is decoded by the ATir, it is ignored so other remotes with different ID values can be used with no modification to the code. A universal remote control can be configured to work with the ATir, as well as extra remote controls that you may have that are not being used (that modulate at the same frequency and use a common 32-bit frame format).
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