Sound-Controlled Time Delay LED

Project Number: 75

OBJECTIVE: To control an LED using sound.

Description: Use the circuit from Project #74. Connect the whistle chip (WC) to points A1 and C1 on the base grid, then remove the photoresistor (RP). Turn the slide switch (S1) on and clap your hands or talk loud near the whistle chip, the LED (D1) will light. The whistle chip has a piezocrystal between the two metal plates. The sound causes the plates to vibrate and produce a small voltage. The voltage then activates the music IC (U1).