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Clap Switch

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Christy

New Member
Hey everyone,
I have a bit of a problem, I am using a clap switch for my project.The attachment is included. In the current clap switch, i do not want to use the whole circuit but till the end of the second 555 timer output...in the this circuit it uses a 9V dc supply but i want to use a 12Vdc, could someone help me on how to calculate those resistor values and capacitors excluding the resistors R7 and R9 and the capacitors C3 and C5
It would be much appreciated.
Thanks.
 

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audioguru

Well-Known Member
Most Helpful Member
People who made the circuit say that it starts all confused because the CD4017 is not reset when the power supply is turned on.
Then after many hand claps it starts to work but responds to almost everthing that makes sharp loud sounds including dog barks and a bouncing ball.
 

Christy

New Member
Thanks for the reply audioguru, but i dont wanna use the whole circuit, i just want to use it till the output of the 2nd 555 timer and not the rest of the circuit, because I'm connecting the output of the second 555 timer to something else...could you please help me on how to calculate the values of the resistors and capacitors when i use a 12V supply instead of 9V
 

Christy

New Member
thank you for the reply. So I could use the same resistor values and capacitors regardless the supply voltage?
 

audioguru

Well-Known Member
Most Helpful Member
thank you for the reply. So I could use the same resistor values and capacitors regardless the supply voltage?
Yes. But the minimum supply voltage is 4.5V and the max allowed supply voltage is 16V for an ordinary 555. A Cmos 555 has a minimum supply voltage of 1.5V or 2.0V and a max allowed supply voltage of 15V.
 

DerStrom8

Super Moderator
I think I've tried this circuit before, and as AG said, it responds to any loud noise. It is definitely not the best clap switch circuit.
Der Strom
 

BrownOut

Banned
I doubt that any of the 'clap' switches will be sophistacated enough to discern an hand clap from a dog bark, etc. The trick will be to use it in a normally quiet area. One might adjust the input network to T1 to set a high threshold for the loudness of the sound to trigger the device. ie lowering the value of R4 might help.
 
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Christy

New Member
Thanks guys.Damn, responds to any noise???that sucks!i will try it in a quiet area as Brownout mensioned....But can u guys help me on how they calculated those resistor and capacitors values until the output of the second 555 timer using that 9V supply , because my lecturer wants me to show how the values were calculated.I tried but i struggled. thanks
 

DerStrom8

Super Moderator
Thanks guys.Damn, responds to any noise???that sucks!i will try it in a quiet area as Brownout mensioned....But can u guys help me on how they calculated those resistor and capacitors values until the output of the second 555 timer using that 9V supply , because my lecturer wants me to show how the values were calculated.I tried but i struggled. thanks
If your lecturer wants you to show how the values were calculated, shouldn't that mean that he has taught you already? I can give you the equations, but it seems as though you should already know them.

High time period (T1) = 0.693 * (R1+R2) * C
Low time period (T2) = 0.693 * R2 * C
Frequency = 1.44 / ( (R1+R2+R2) * C)

This all comes from THIS site, or you can just google it in case you need more help.
Good luck!
Der Strom
 
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Christy

New Member
Thank you DerStrom...My lecturer as not taught me this,it's a project I'm doing that includes a clap switch.By the way DerStrom,could you explain to me on how to get those resistor and capacitor values at the amplification side,in the very beginning and how would I know the values I calculated are correct or not?
 

DerStrom8

Super Moderator
By the way DerStrom,could you explain to me on how to get those resistor and capacitor values at the amplification side,in the very beginning and how would I know the values I calculated are correct or not?
The first 555 is not an amplifier, traditionally speaking. It is wired as a monostable "trigger." When a certain level of "noise" is detected by the mic, it forces pin 2 low, triggering the output. You can google "monostable 555 timer" or something like that to get the calculations.
Der Strom
 
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BrownOut

Banned
The first 555 is not an amplifier, traditionally speaking. It is wired as a monostable "trigger." When a certain level of "noise" is detected by the mic, it forces pin 2 low, triggering the output. You can google "monostable 555 timer" or something like that to get the calculations.
Der Strom
I think he was asking about the input transistor stage.
 
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DerStrom8

Super Moderator
I think he was asking about the input transistor stage.
Oh, sorry. I guess you're right :p
Anyone else able to answer that? I'm not very good with the operation of audio circuits :D
AG?
 

BrownOut

Banned
R3 and R4 create a voltage generator by the equation:

VB = VCC*R4/(R3 + R4), for the values in the circuit: V = .9V.

The output resistance of the voltage generator is ~= 240K, the smaller of the two resistors.

IB would then be the generator voltage minus .6V, which is the approximate VBE of the transistor, divided by the generator resistance: IB = (.9 - .6)/240K = 1.25uA.

Assuming Beta of 100; IC = 125uA

And finally, the collector voltage in the quiescent state: VC = 9 - 125uA*3.3K = 8.6V.

So the transistor is just barely conducting. A signal from the mic causes the transistor to conduct a higher current, which is then sensed by the first timer, and causes it to trigger.

The -3db frequency of the C1 network is, using time constants is:

1/2pi*R, where R is R2 + ((R1 + R3)||R4)

And for C2:

1/2pi*R, where R is R5+R6.
 
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