This infrared audio transmitter uses infrared impulses modulated in time (pulse width modulation). Modulated signal is produced by comparing the pure audio signal with a triangular high frequency signal, using comparator Cl.
For a large range, the current through the LED must be high. Because LEDs can not drive continuous high current, pulses should be short, and it must be the reason for using pulse width modulation (PWM). Pulses are generated by XOR gate IC2d, which compare the original PWM signal delayed by R5-C3-IC2c.
This wireless audio receiver circuit is designed using common electronic components and allow reception of an audio signal, without using electrical wires. The infrared receiver can be used with infrared transmitter presented in a previous article.