Circuit that allows snap of fingers creates equal flash from LED?

So, any simple/single transister or darlington/minimum parts type solutions...that would fit in a AA battery compartment?

You need an amplifier that uses supply current all the time. Maybe you can find a low power amplifier IC. Then when it receives a signal from the microphone it feeds a rectifier that produces a DC voltage that turns on the transistor.

I will give that some research Audioguru, thank you.
And Colin, I still thank you for the attempt. You were still way ahead of me!
I still have a lot of learning to do.

I guess there is just NOT a transister sensitive enough to use the microphone to activate it (momentarily) as a switch...as I had hoped/imagined.

Is something like this that you want?

I made this with parts that were laying on my work table in less than five minutes without doing any math. And with two simple BC547Cs.

Of course it could be improved. And a lot. With emitter resistors and stuff.

This was just to show that no, you don't need an IC to do that.

What's best, or simpler, is a matter of taste.

Transistors work fine.

Edit: There are two major mistakes in the schematic, which are:
1 - I forgot to draw the Vcc (in this case, 5V from a DC power supply)
2 - The resistor in series with the LED is a 39R/1W resistor.

Caster, it's probably obvious to you experts, but where does the Vcc input connect exactly?

So you quickly built it, and it worked!? A snap of the fingers resulted in a flash from the LED?

caster.cp said:

I made this with parts that were laying on my work table in less than five minutes without doing any math. And with two simple BC547Cs.

Click to expand...

It is almost like the circuit designed by Colin.
The first transistor is turned off but heat will turn it on and if you scream into the mic or hit it with a hammer. The 470uf capacitor is 1000 times too big.

My circuit will not work. Don't try it.

audioguru said:

It is almost like the circuit designed by Colin.
The first transistor is turned off but heat will turn it on and if you scream into the mic or hit it with a hammer. The 470uf capacitor is 1000 times too big.

Click to expand...

Yes, the heat problem could be easily solved with a emitter resistor bypassed to ground by a capacitor. The capacitor values was chosen following a simple rule: there were two caps laying on my table, one 470u and one 10u

This was just to show that it can be done with transistors.

Have you seen the video I attached, also?

Its sensibility is good enough.

Caster,
There is an error in the header of your ZIP file so it cannot be unzipped.
I didn't know it is a movie of your circuit working.

Yes, Caster, I couldn't get the zip file to open.
I'm anxious to see it though!

Does it show where you brought the Vcc in at? And also please show me how you would add the emitter resister/capacitor if you would.
I am anxious to get a working circuit built, but I'm pretty new to this...so you kinda have to spell it out for me.
I had hoped it could be done with a minimum of parts, and I think what you have designed can be made to fit in my space required.

Thank you for the help!

In Caster's circuit both transistors are not biased correctly so they do not work.
His and Colin's first transistor are turned off so they cannot amplify the low level signal from the mic unless you scream into it or hit it with a hammer.

If the first transistor is biased properly so it is an amplifier then its continuous current will kill your tiny battery in a few minutes. You need to find an amplifier circuit that uses a very low amount of supply current.

A "Keys Finder" project has an amplifier that uses a low amount of supply current.
The Keys Finder project at Electronics-Lab is not suitable.

Okay, if it can't be done...then I guess it can't be done.

BUT, It just seems odd that I can design a transister switch circuit that will activate and turn on an LED from the voltage on my skin (a "touch switch"), but that the output from a microphone is NOT enough to do it.

REMEMBER, the flash from the LED doesn't have to be proportional to the finger snap audio!!!

It just has to turn on the LED for a moment (flash). This could be a flash that's only as long as it takes a capacitor to discharge.
A super small "clapper" circuit, that doesn't stay on...but only results in a SINGLE FLASH with each clap.

So, it doesn't actually HAVE to be an "amplifier" circuit (per se)...just a "switch circuit" that will FLASH the LED for a fraction of a second.
JUST a SINGLE FLASH each time a loud snap occures.

Just a "clapper" that doesn't stay on...but only results in a SINGLE FLASH per each clap.
BUT, the limiting factor is that the entire assembly has to be SMALL to fit in a AA sized compartment...that's why I was hoping for a small single transister type circuit. But, if it can't be done...without a large amplifier circuit...it won't fit in a AA compartment.

Hope the video works now. It's exactly that circuit shown in the schematic.

And about the current consumption, it all depends on the application of the circuit. If you intend to let the thing on all day long, then I agree with audioguru. If you just want to build something fun to show your friends and stuff, than don't care about it.

I completely agree with the legendary Mr. Miyagi in these matters: "First learn stand, then learn fly. Nature rule." If you don't know even how a transistor work, then it would be much more profitable if you built a simpler circuit and understand what's going on than to build something overly complex just mimicking some schematic you found on the web.

Again, it depends on what do you want =).



Answering your first questions: The vcc goes at the "top" of the circuit, conected with all those "top" resistors.

The emitter resistor is a kind of negative feedback added to the circuit, that reduces the gain but makes the circuit much more stable to temperature variations.

The whole temperature problem can be resumed to the following:

The current flowing through the colector tends to get much higher at higher temperatures. Increasing the temperature also makes the base-emitter voltage drop become smaller. This effects makes the overall current flowing through the transistor increase. The increase of the current increase the power dissipation, that increases the temperature, that increases the current even more... You see the problem, don't you?

Placing a resistor betwen the emitter and ground makes everything much better.

When the collector current increases due to the temperature, the voltage at the resistor in the collector also increases (as V = R*I). This reduces both the Collector-emitter and the base-emitter voltage, almost solving the temperature thing.

You can calculate some parameters related to this phenomenon, called the thermal stability factors. Mathematically speaking: if you know the partial derivative of a certain circuit parameter (such as the collector current, for instance), with respect to the temperature, than you can quantify how big is the problem at your circuit.

Simplifying things: this parameter, called S at the book in which I studied this at college (Millman....), can be approximated to 1 + Rb/Re, where Rb is the thevenin's equivalent resistance at the base of the transistor, and Re is the resistance at the emitter.

The smaller the S, the better the circuit. As you can see, increasing the Re makes the circuit more stable.

The problem is that this resistor makes the voltage gain smaller. So, to make this compensation not interfere at signal frequencies, we bypass this capacitor to ground, so that it "vanishes" at higher frequencies (because the capacitor can be thought of as being a short-circuit at high f).

My advice: build something you can understand, and really make an effort to understand it. You'll profit a lot from the experience. The biggest mistake some people make when they begin to learn electronics is to think that electronics is just schematic-mimicking.

If you can learn something new, than you are onto something good.


Castilho

Isn't a loud clap much louder than a finger snap?

The output level from a microphone is very small and needs a preamplifier turned on all the time so it can listen for your finger snap. The preamplifier's current will kill your tiny battery soon unless you find a preamplifier circuit that uses a very low supply current.

I suggested looking for a "Keys Finder" circuit that also has a preamplifier that is turned on all the time.

The sound will actually be a fairly loud metalic snap (like a closing door), and I anticipate about one snap/flash per minute would be necessary...for about 2 hours of battery use.

If I end up getting 2hrs use (at that rate) out of 3 button-cells (4.5v total) I will be happy.

PS: I've been buying LED reading/book lights at the doller store for $1 that include 3 button batteries (similar to CR123's I think). Granted, they are NOT Energizer brand, but they're also 3 for a buck. (with a free LED light thrown in)
If those last me 2hrs for the dollar I spend on them...hey..I'll be happy!

Try this circuit:

Colin's new circuit has a current drain of only about 0.5mA by the electret mic so button battery cells will last for days.
But since the first transistor is turned off then it takes heat or a very loud sound into the mic to turn it on.

Well, it's worth a try...now to try to squeeze the parts/circuit into the tiny space of a AA battery compartment.
I sure do apporeciate all the help from you folks, and I am learning more everytime I get on this website. I can understand how audioguru can get a post count in the 18K range!
This stuff is cool!!! The more I learn, the more questions I have to learn more!

Thanks folks! Time to build it and try it out!!!
Bought myself a new soldering gun yesterday (and a desoldering gun for "scrounging" parts from the massive amount of old stuff that doesn't work that I never throw away)


I'll play with it and see if the circuits shown have the sensitivity for the application, and I'll also keep my eye out for a tiny "Key Finder" circuit that might work as well. I can at least LEARN from the attempts.

Rookie question...

One more question, and it's probably a kindegarden-level question...but I'm still learning so here goes:

Do the 1M+100K resisters effectively act as enough of an "open" to prevent the 1M+100K resisters from completeing a circuit back to the battery, and draining the battery?

I understand the 10K+microphone loop is going to drain current, but won't the loop that consists of the 1M and the 100K also drain some current?
Or is that such a high resistance that it almost acts as an "open"? And if it does almost act as an "open" for that reason...what do you need that circuit path for? Why not just remove the 1M/circuit path completely?

In Caster's circuit (that worked but may drain battery?) that same area adds up to 43.7K...so even less...

Or is my math/understanding wrong on 1M+100K total resistance through the 1M circuit path?
I think I understand the circuit, except for THAT loop...
And, will the battery see the 10K being in parallel with the 1M, cause the 1M+100K path to be even less?
What is the resistance in the red loop, or can it even be looked at that way?

**broken link removed**

In other words, what exactly is that 1M/circuit path there for? Do you even need that circuit path, or can everything on the BASE side of Transister1 go through the 10K/blue loop? Why not take the 1M resister out completely?

arizonaguide said:

I can understand how audioguru can get a post count in the 18K range!

Click to expand...

I didn't look. I have many more posts on the other electronics chat sites I visit every day.

Bought myself a new soldering gun yesterday (and a desoldering gun for "scrounging" parts from the massive amount of old stuff that doesn't work that I never throw away)

Click to expand...

I used a soldering gun to scorch electronic parts when I was 12 years old. It soldered things very poorly. Then I got a cheap soldering iron that also got way too hot. Then I got the Weller temperature controlled soldering iron that solders and unsolders perfectly, is 44 years old and it still works perfectly. It is still manufactured and sold today.