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Connecting a 8 ohm buzzer to a 555 timer : help !

Hi !

I am having A LOT of trouble to make this buzzer buzz. I am building a rain detector. When there's water the system closes, the LED lights and the buzzer buzzes, expect its not buzzing. I do not understand what I did wrong, I reconnected the circuit 10 times. Please help me. I am using a 9 V battery, a 8 ohm speaker.

Circuit diagram : https://ibb.co/s3kf28P
 

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audioguru

Well-Known Member
Most Helpful Member
As I said in the other forum your wires are a mess. Get rid of the breadboard and use a neat and tidy pcb.
The schematic shows an 8 ohm speaker (not a buzzer) that will overload and destroy the 555 oscillator which might have already happened.

Electronics Hub is a website done by students (in India?) with many errors. Use a website done by engineers.
 
As I said in the other forum your wires are a mess. Get rid of the breadboard and use a neat and tidy pcb.
The schematic shows an 8 ohm speaker (not a buzzer) that will overload and destroy the 555 oscillator which might have already happened.

Electronics Hub is a website done by students (in India?) with many errors. Use a website done by engineers.
So i need to get a new timer and a new buzzer? It is too late to change of circuit diagram and I didn't know this was not going to work. Thank you for responsding !
 

audioguru

Well-Known Member
Most Helpful Member
A new timer will also quickly burn out. The bad translation says buzzer instead of speaker.
You need a circuit designed in The West by an engineer who knows English and all the details about electronics, not by a student over there.
 

audioguru

Well-Known Member
Most Helpful Member
I do not know if your rain has enough salts in it to be conductive enough. My rain doesn't. Maybe the students used sea water.
After replacing the burnt out 555 a complementary pair of medium-power transistors as emitter-followers can be added between the 555 output and the 100uF output capacitor.
The 100pF capacitor C5 should be 10nF.
 

AnalogKid

Well-Known Member
Most Helpful Member
the LED lights and the buzzer buzzes, expect its not buzzing.
What does this mean? Please describe in detail how the circuit is behaving.

Is the circuit supposed to drive a speaker with a tone, like a beep? Is the tone supposed to go on and off, or stay on continuously?

Is the circuit supposed to make a tone for a few seconds, and then stop even though the sensor still is wet?

If so, there are better ways to do that. The basic problem is that all three transistors are acting as emitter followers rather than as saturated switches. this makes the circuit performance very dependent on the performance of each transistor as a linear amplifier. This performance changes from device to device, and with temperature, making the overall performance unpredictable.

Also, operating on 9 V rather than 12 V can matter, again because the transistors are not acting as switches. The problem might be that the voltage at the Reset input is not going high enough to enable the 555. A quick thing to try is to delete (short out) D1.

ak
 
What does this mean? Please describe in detail how the circuit is behaving.

Is the circuit supposed to drive a speaker with a tone, like a beep? Is the tone supposed to go on and off, or stay on continuously?

Is the circuit supposed to make a tone for a few seconds, and then stop even though the sensor still is wet?

If so, there are better ways to do that. The basic problem is that all three transistors are acting as emitter followers rather than as saturated switches. this makes the circuit performance very dependent on the performance of each transistor as a linear amplifier. This performance changes from device to device, and with temperature, making the overall performance unpredictable.

Also, operating on 9 V rather than 12 V can matter, again because the transistors are not acting as switches. The problem might be that the voltage at the Reset input is not going high enough to enable the 555. A quick thing to try is to delete (short out) D1.

ak
The online document doesn't say much: an alarm is supposed to go off for some time and then stop. Link to the project : https://www.electronicshub.org/rain-alarm-project/

When you say short out D1, you mean remove it from the circuit ?
 

audioguru

Well-Known Member
Most Helpful Member
In the other forum he said, "The led is working but not the buzzer."
Simple arithmetic shows that the 555 is still overloaded if the battery is only 9V, but then the transistors in the circuit might not work with only 9V.
 

danadak

Active Member
Trying to drive an 8 ohm speaker directly with 555 ill advised.

Power average somewhere around 1.6W, cook steaks on the 555 at that level.

Use a much smaller coupling cap to speaker could resolve, at reduced volume, or use
external power device, bipolar or MOSFET. Or reduce Vcc to 555.

1638016350952.png



Waveform is speaker power.


Regards, Dana.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Trying to drive an 8 ohm speaker directly with 555 ill advised.

Power average somewhere around 1.6W, cook steaks on the 555 at that level.

Use a much smaller coupling cap to speaker could resolve, at reduced volume, or use
external power device, bipolar or MOSFET. Or reduce Vcc to 555.

You rather missed the standard method - simply stick a resistor in series with the speaker - you do the same with mico-controller pins as well. Needless to say volume is reduced considerably, hence AG's suggestion of driver transistors.
 

danadak

Active Member
You rather missed the standard method - simply stick a resistor in series with the speaker - you do the same with mico-controller pins as well. Needless to say volume is reduced considerably, hence AG's suggestion of driver transistors.

I did not miss in his original circuit a C was used. In fact used the same value he used.
Focus was on power he was experiencing. And I concur, R's are used frequently to limit
current flow. But as you can see sim not exact, was having problems with sim working
with high valued R timing values., still looking at that.

Regards, Dana.
 
I did not miss in his original circuit a C was used. In fact used the same value he used.
Focus was on power he was experiencing. And I concur, R's are used frequently to limit
current flow. But as you can see sim not exact, was having problems with sim working
with high valued R timing values., still looking at that.

Regards, Dana.
thank you ! where in the circuit should i plug the rain detector and the led ?
 
You rather missed the standard method - simply stick a resistor in series with the speaker - you do the same with mico-controller pins as well. Needless to say volume is reduced considerably, hence AG's suggestion of driver transistors.
so should i just add a resistor in series with the capacitor and the buzzer ? if yes, what value ? before or after the capacitor ? thank you
 
Replace cap you show in series with speaker with a 300, 330 ohm R for starters.

Regards, Dana..
OMG i took out the diode, added a 1k resistor in front of the cap and it worked ! The sound is reallly weak but thank you so much you don't even realize how much i appreciate it. If replace the speaker with a buzzer, will the sound be louder ?
 

danadak

Active Member
Without calculations the R is probably safe to ~ 50 ohms, so try at 300
and drop values until you get loudness you want. But stay above 50 ohms
so. You don't need the cap anymore just the R in series with speaker.

I did a sim and not crazy about response. Do you want led to snap on/off
or a response like sim shows ?

1638034299916.png


Regards, Dana.
 

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