Brief passive buzzer controlled by 555 timer astable multivibrator set by light dependent resistor LDR circuit

Table of Contents

The passive buzzer depends on pulses to make noise. A slow rate of voltage changes makes clicking noises, while fast enough voltage change makes a steady audible tone.

The 555 timer wired in astable mode with a light dependent timing resistor (LDR), is an easy way to get a steady on/off square wave.

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Diagram

Simple passive buzzer controlled by 555 timer astable multivibrator set by light dependent resistor LDR schematic diagram by electronzap electronzapdotcom
Simple passive buzzer controlled by 555 timer astable multivibrator set by light dependent resistor LDR schematic diagram by electronzap electronzapdotcom

Passive buzzers need a changing voltage to make sound.

While the astable 555 timer capacitor is charging towards 2/3 supply voltage, the output is high.

When capacitor hits 2/3 supply voltage, the output goes low and the capacitor discharges through pin 7 (discharge pin) until it drops to 1/3 supply voltage.

Output goes back high again once capacitor drops to 1/3 supply voltage and the capacitor starts charging again.

The primary factor setting the timing for any given capacitor is how much light is falling on the light dependent resistor, which sets it’s resistance.

The faster the timing goes (brighter LDR) the higher pitch or faster clicking of the buzzer.

Slower timing, due to a darkened LDR will result in slower clicks or a lower pitch buzz.

Large capacitors are more likely to click while smaller capacitors are more likely to buzz.

Video

Quick passive buzzer circuit using 555 timer astable multivibrator controlled by photoresistor

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