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

[KhaledOsmani]

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

 

[Audioguru]

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.

 

[KhaledOsmani]

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?

 

[Audioguru]

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.

 

[KhaledOsmani]

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?

 

[Audioguru]

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.

 

[KhaledOsmani]

This all was tried. Same output. Continuous noise

 

[Audioguru]

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?

 

[KhaledOsmani]

Speaker noise:

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

 

[Audioguru]

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.

 

[KhaledOsmani]

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

what is your major of study?