Using a CMOS 555 timer, you can drive seven high-brightness LEDs from a single 1.25V cell. Analog switch converts 555 timer into pulse-width modulator Added CMOS switch enhances a PWM oscillator. Use ...

You’re right. It describes the standard 555 clock oscillator for the transmitter, and in the last sentence of that section, says, “Also you will need to build one more for the receiver.” ...