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What is the difference between a SPEAKER and a PIEZO BUZZER, and how to choose

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KhaledOsmani

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Hello,


This circuit works as a light detector,
once there is light fallen on the LDR, the speaker buzzes

But, when connection this speaker alone, and supplying a voltage across its terminals, no sound is obtained. contrary to the buzzer, that once supplied, a sound occurs.

what is the difference between a speaker and a buzzer, why to choose a buzzer in this circuit, and why this speaker make no noise once supplied?

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This is the circuit
 

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EDIT:

A piezo beeper is a piezo transducer with a transistor oscillator inside.
The transducer beeps when the oscillator is powered by a DC voltage.

The output of the 555 produces a buzzing tone when there is light.
The 555 in the circuit is overloaded by most low impedance speakers, it should have a resistor in series with the speaker to limit its current to 200mA.

A piezo beeper might not beep when fed the buzzing tone from the 555 instead of DC.
 
Last edited:
So there wouldn't be any sounds at the output even if light is fallen on the LDR?

There is a mistake in the circuit? can I replace the speaker with a piezo?
 

The circuit is almost correct except most speakers will overload the 555.
I corrected my wrong text.

If you replace the speaker with a piezo transducer then it might not be able to produce the fairly low frequency from the 555.
You can replace the 555 circuit with a piece of wire and the LDR and power supply might be able to make a piezo beeper beep when there is light.
 
I've connected the circuit as it is, and made sure using a multimeter.

the output is: the speaker always have a sound on, either there is light, or there isn't any light, no matter what the value of the pot is set to...always sounds on...

why and how to solve?
 

The 555 is reset and stops oscillating when its Reset pin 4 voltage is as low as 0.3V for some 555 ICs.
Then you need darkness to produce a very high resistance for the LDR, or a reduced resistance for the 4.7k resistor and-or the pot.
 

This all was tried. Same output. Continuous noise
 

When pin 4 of a 555 oscillator has its voltage near 0V then the oscillation stops because then the 555 is reset.
When you connect pin 4 to 0V then does the oscillation stop?

You said "continuous noise". Is it the buzz sound from the 555 driving the speaker or is it interference maybe even mains hum?
 

Speaker noise:

Either the LDR is at full darkness/complete light
Either the pot is set to max/min/in between
 

Speaker noise:

Either the LDR is at full darkness/complete light
Either the pot is set to max/min/in between
I see the problem.
The datasheet for a 555 says that the minimum voltage on pin 4 for all of them to stop oscillating is 0.4V.
The maximum pin 4 current is 0.4mA. Then for the oscillator to stop the LDR must be a very high resistance, the pot must be zero ohms and the 4.7k resistor must be 0.4V/0.4mA= 1k ohms.
So change the 4.7k resistor to 1k ohms or less.
 

thank you man, and greetings to your efforts and logical thinking. good job.

what is your major of study?
 

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