/ / Introduction
Tremolo is the rapid oscillation in volume that gives the guitar its cool vibrating sound.
The heart of the Blinkie Tremolo effect is a homemade optoisolator made from an LED and a Light Dependent Resistor (LDR).The LDR controls the volume of the audio signal. As the LED shines on the LDR, the resistance drops and the audio comes through. As the LED dims, resistance increases and the sound fades. The 555 timer circuit rhythmically pulses the LED, which in turn, pulses the volume, giving you the vibration effect.
Source:David Erik Nelson, Snip, Burn, Solder, Shred and Ranjit Bhatnagar