Palm Pilots are just one of the devices that use the IrDA
standard for infrared data communication. Most Desktop PCs are not equipped with an IrDA interface so this simple circuit conveniently converts the PC serial port into an IrDA receiver. The circuit needs to detect
and stretch the received infrared pulses so that the output signal conforms to the standard serial data format. The circuit is designed to operate at 9600 Baud and uses just two NPN transistors and a phototransistor.
The 22-nF capacitor performs the job of lengthening the signals. It is important to ensure that the DTR signal is set to a high state on the serial port settings because this signal is used as the power supply to the circuit.
The sample program listed below is written in HotPaw Basic for the Palm and tests the interface by sending a short greeting followed by a sequence of integers.
open “com1:”,9600, ir as #5
for n= 1 to 100
a= fn wait(1)
NPN transistors are a type of bipolar transistor with three layers that are used for signal amplification. It is a device that is controlled by the current. A negative-positive-negative transistor is denoted by the abbreviation NPN. Since most of the charge carriers in N P N transistors are electrons, their electron mobility rates are high. N P N transistors provide better conductivity than P N P transistors for this reason. Due to their fast switching rates, N P N transistors are preferred for switching applications.