Feedback on a sound controlled light circuit

[Rainier9]

Hi guys, I need to design a circuit capable of activating a light if there's a sound source.

Sound= Light on
No sound at all = Light off

Here's an attempt (see attachment). The AC voltage source is simulating an audio source. Then i converted it to DC so it could activate both transistors shown in the figure. Wich wouldl then activate a Relay that would activate an AC light.

Please tell me your feedback about the circuit, and I got a question as of how the circuit could affect the output signal (as in noise and etc).

Any feedback is good, thanks!

 

[berkeman]

Hi guys, I need to design a circuit capable of activating a light if there's a sound source.

Sound= Light on
No sound at all = Light off

Here's an attempt (see attachment). The AC voltage source is simulating an audio source. Then i converted it to DC so it could activate both transistors shown in the figure. Wich wouldl then activate a Relay that would activate an AC light.

Please tell me your feedback about the circuit, and I got a question as of how the circuit could affect the output signal (as in noise and etc).

Any feedback is good, thanks!

What are Q1 and R2 meant to do? Otherwise, it looks reasonable. Is the voltage souce meant to represent the output of the microphone amplifier circuit?

 

[Rainier9]

Yes, the AC Voltage source represents the output of the microphone/instrument amplifier.
Q1 and R2 are supposed to amplify the converted DC current, so it would switch the second transistor from off to on.

 

[berkeman]

Yes, the AC Voltage source represents the output of the microphone/instrument amplifier.
Q1 and R2 are supposed to amplify the converted DC current, so it would switch the second transistor from off to on.

Then Q1's collector should go someplace else if you want current amplification. What should Q1's collector be connected to if you want to tap another source of higher current than the output of the microphone amplifier?

 

[Rainier9]

I'm kind of sorry man, I can't really understand your question (Spanish is my first tongue). Could you please rephrase it?

I do get what you mean about Q1 though, what if I connect the DC current to the Base of Q1 instead of its collector?

 

[berkeman]

I'm kind of sorry man, I can't really understand your question (Spanish is my first tongue). Could you please rephrase it?

How do you say collector in Spanish? Just kidding. I took 3 years of Spanish in high school, but that was before my EE education...

I do get what you mean about Q1 though, what if I connect the DC current to the Base of Q1 instead of its collector?

To get amplification, you need the transistor's collector connected to a higher power source than just the input small signal source. Otherwise, you could just eliminate the transistor and connect the rest of the circuit to the output of the rectified microphone amplifier (which might be enough to still turn on your relay circuit, but maybe not).

What is the relay driver transistor's collector connected to (through the relay coil)? Why?

 

[Rainier9]

To get amplification, you need the transistor's collector connected to a higher power source than just the input small signal source. Otherwise, you could just eliminate the transistor and connect the rest of the circuit to the output of the rectified microphone amplifier (which might be enough to still turn on your relay circuit, but maybe not).

Yeah, I was thinking about connecting the rectified microphone/instrument amplifier to the base of the transistor and then adding a DC voltage source to the collector to amplify the current (just to make sure it will be enough).

What is the relay driver transistor's collector connected to (through the relay coil)? Why?

If the current that goes thru the base of the second transistor is enough to ''activate it'' then it would switch from ''off'' to ''on'' and would charge the Coil of the Relay and thus activating the AC light.

 

[berkeman]

Yeah, I was thinking about connecting the rectified microphone/instrument amplifier to the base of the transistor and then adding a DC voltage source to the collector to amplify the current (just to make sure it will be enough).

Yep.

 

[Rainier9]

Do you then think that I should still connect the first transistor's collector to the base of the second one?

 

[Jiggy-Ninja]

So the signal from the microphone is half-wave rectified, smoothed with a capacitor, and sent through what seems to be something like a Darlington pair of transistors to amplify the current to drive the relay, is that correct?

What is the peak voltage from the microphone? The signal has to travel through a diode and two BE junctions, so you'll need at least 2.1 V to forward bias all those. If it's a 3V peak-to-peak signal it won't work, but 3V peak would be fine.

And what Berkeman is trying to say is that the Q1 collector should be connected to something like your 12V power supply. If you connect the base and collector to the same source, the transistor isn't doing anything and you aren't getting any amplification.

Depending on how much you can load the microphone and how much current the relay needs, you might not even need two transistors.

 

[Rainier9]

Yep, thanks for answering.

I already tested and it worked without one of the transistors! The thing is that I may have to amplify the signal once more, since with low peak voltage songs as Instrumental/Classic ones it won't work. Haven't tested with an actual stage mic or electric instrument yet, will do so in this week, but I guess it's right to assume it will work since those devices will probably deliver more Power than an IPhone, which was how I previously tested the circuit.

Also, I changed the rectifier to a bridge rectifier. Better resulst overall. Here's another idea: After I rectify the signal I was thinking about adding a 5V voltage regulator... what do you guys think?