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Please help modified a circuit

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cannibal

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Hello

I am using Dark activated circuit which is in black color in the attached image

but I thought it would be better to use buzzer with timed one

so I added other circuit which is blue color in the attached image
it has 555 IC

1) I would like to know if the circuit will work or not so I won't lose money buying components

2) how to make the whole circuit working with B1 or B2 only NOT two source?

3) what value should be for R9 ???
 

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It won't work because the 2 circuits are only joined at one point.

You have not explained what you're trying to do.

You can easily run it from one battery. Just connect the 0V and V+ lines.
 
The circuit will active the buzzer when there is no light on photo resistor

I modifiy it again please check
 

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The 555 draws a fair amount of current even if it is not doing anything. A Cmos 555 (LMC555, TLC555 and ICL7555) draw almost no current.

The 555 does not time out when its pin 2 is low. Add a coupling capacitor to pulse pin 2 low then use a pullup resistor.
 
I have this type

IC

D&P
NE555
0531


Do I have to add something ??

and could you please show me how to add a coupling capacitor to pulse pin 2 low then use a pullup resistor
 
You should remove R10 and D2. These should not be in series with the battery.

Do you want the LED to glow when the Buzzer is sounding?
 
I fixed the LED and R10

the circuit is working but not correct


this what happens

when there is light there is some low sound from buzzer which should not be

when there is dark the buzzer sound louder which is correct
 
If Q8 is connected upside down then it would act like a 7V zener diode in series with the buzzer and make it have a low level sound.

Then when it turns on it will have a small amount of current gain which makes the buzzer a little louder.
 
Hi

I just fixed the circuit problem

Now it’s working like I want

But still one more problem

When switching the 9V ON, the buzzer starts making sound even if there is light on photoresistor
but it will stop after some time because of 555IC and then the circuit functioning with no problem


HOW can I solve the buzzer problem (when the circuit starts up) ????
 

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Now you have pin 2 of the 555 at a low voltage all the time. With pin 2 low then it makes its pin 3 high which turns on Q3 and the buzzer all the time.

Pin 2 of a 555 must be pulsed low for a moment to trigger it then it must return to being high.

The signals at the emitters of the transistors are at a very low level. The trigger pin 2 of a 555 needs a high signal level.
 
Pin 2 of the 555 is connected to a 47 ohm resistor (R6) to ground. Its voltage is about 0.08V. Pin 2 needs to be at least 6V for the 555 to time-out.
 
Is this what you want?
 

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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
 
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
 
Last edited:
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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