Table of Contents
One way Passive buzzers can be switched on and off is with an NPN Bipolar Junction Transistor (BJT). The NPN BJT can be controlled by a 555 timer output. An Astable mode 555 timer’s high and low output speed can be set by a Light Dependent Resistor (LDR).
- Passive buzzer makes clicking noises while it is turned on/off slowly.
- Speeding up the clicks enough turns them into a buzz. The buzz gets higher pitched as you keep speeding them up (at a higher frequency).
- Brighter light on the Light Dependent Resistor (LDR) charges and discharges the capacitor faster than lower light.
- Capacitor discharges through pin 7 (discharge pin) to ground while output is low.
- 555 output is set low after the capacitor rises above 2/3 of the supply voltage.
- There is a high output after the capacitor drops below 1/3 of the supply voltage.
- NPN Bipolar Junction Transistor (BJT) switch turns on when the 555 output is high, and off while the output is low.
- Current flows through the buzzer when NPN BJT is on. No current flows through it when the NPN BJT is off.
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