audioguru

Is this what you want?

Attached Images

buzzer when dark.PNG (12.8 KB, 19 views)

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Uncle $crooge

cannibal

hello

I tested the circuit you provided in breadboard

I faced these problems

1) the buzzer making sound when there is light and that should be revered
the buzzer should make sound if it's in dark

2) the buzzer not stoping making sound

3) the sound of the buzzer is too week

ljcox

I don't see why you need Q3 and R8.

Connect the buzzer to the 555 pin 3.

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Len

cannibal

hello
with out Q3 and R8 it won't work

Mr audioguru

I tried to test again your circuit and it's working fine
but facing one simple problem

1) the buzzer won't stop when it get activated

I appricate your help

audioguru

In my circuit the 555 is a monostable exactly like in its datasheet. The 10k resistor holds its pin 2 high so it can time out and stop the buzzer.

When it gets dark then Q1 turns off. Then R4 turns on Q2. The collector of Q2 then has a negative-going pulse through the 47nF capacitor that triggers pin 2 of the 555 so it makes a timed output for the buzzer. R4 and R9 are 10k ohms and R5 is 470 ohms.

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Uncle $crooge

cannibal

I did everything that you said but still the buzzer wont stop

please see this

is this the capacitor that I have to use ? the one of 47nF

it's writting on it

473

Attached Images

Image330.jpg (2.5 KB, 8 views)

audioguru

A fuzzy photo without any light is useless.
A capacitor marked 473 is 47nF.

Disconnect everything from pin 2 of the 555 except the 10k resisitor to the positive supply, the 47nF capacitor and the other 10k resistor to the positive supply at the other end of the capacitor. Ground the input for a moment like this:

The 555 should get triggered, the buzzer should sound for the timing then stop when the 555 times out.

Please stay in only one website's forum.

Attached Images

555 monostable timer.PNG (10.8 KB, 12 views)

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Uncle $crooge

cannibal

I done the circuit
and I touched the * to the ground then the buzzer made sound
but didn't stop

there was no timeout for 555

audioguru

Then either the 555 is defective, or the leakage current of C2 is too high or the value of R7 is too high.

If all your questions were on a single website then i could see the values of C2 and R7.

What is the voltage of the battery? Maybe its voltage drops too low when the buzzer is activated.

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Uncle $crooge

cannibal

C2 is 10uF
R7 is 1M (brown black green)
battery is 4.5V

audioguru

Replace C2 because it might have too much leakage current then it will never fully charge. Make certain it isn't connected with backwards polarity.

The minimum operating voltage for a 555 is 4.5v and yours might drop lower when the buzzer is activated. So try a 6V or 9V battery.

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Uncle $crooge

cannibal

I replaced the C2 with new one (10uF)
the polarity connection checked correct

battrey changed to 9V

the problem still
buzzer won't stop when it get activated

audioguru

Maybe the 1M pot doesn't conduct.
Replace the defective 555 IC.

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Uncle $crooge

cannibal

Hello

Just want to make sure before buying new 555 IC

after how many seconds the 555IC should time out ??

because I waited for 2 minutes and no time out

audioguru

Why ask? Simply look on the datasheet.

1.1 x 10uF x 1M= 11 seconds with the pot at max resistance. They show a graph that looks like 8 seconds.
The 10uF capacitor could be actually only 8uF or 12uF and the 1M pot could be only 800k or 1.2M so the time will be somewhere from 7 seconds max to 16 seconds max.

Since you replaced the capacitor and made certain its polarity is correct then either the 555 is bad or the pot doesn't conduct.

Before buying another 555 try a 1M resistor to replace the pot.

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Uncle $crooge