FM Modulator Circuit Using 555 Timer IC

Here is a frequency modulation (FM) circuit that uses a 555 timer in astable mode to generate a sine wave carrier. GCSE students might find it interesting as they are often playing with the 555 timer IC.

The carrier frequency is set using the 5 kΩ potentiometer behaving as a potential divider with one end at Vcc and the other at ground. The frequency of the free running oscillator is set to approximately 455.50 kHz

A DC coupled input signal at pin 5, then modulates the carrier, and the modulated carrier then emerges from output pin 3.