Communication over the IrDA port uses a relatively complex protocol but its possible to send a single character using just a few components. In many cases, this will be sufficient to control a Palmtop. This circuit generates a single pulse of IR light that is interpreted by the Palmtop as a data byte with the value 255. The circuit could hardly be simpler, a 1 μF capacitor is charged via the 27 kΩ resistors and when the switch has pressed this charge will flow through the diode to generate an IR light pulse.
The values have been optimized for a communication speed of 9600 Baud but the actual pulse length is not critical. The listing shows a simple receiver program for this IrDA signal. The IR interface is opened with the command ir and the line get$(#5,0) reads a single byte from the interface, if nothing has been received it will return –1. Each time a character is received a counter will be incremented and displayed on the screen and a short sound will be generated.
open “com1:”,9600,ir as #5