In the “Happy when clapping cap”,
(see the cap on the GOSSIP project page: http://www.contrechoc.com/garments/projectPage.htm)
we used a mic as a sensor, an electret mic, to register the sound of clapping. To get the signal we used the Led organ Velleman kit
called # MK103 SOUND-TO-LIGHT UNIT (see http://www.mainelectronics.com/kiltsvelleman.htm )
This kit is an amplifier of three stages with transistors. Since all the parts are in the box, and a PCB with it, it is quickly soldered. And it works easily, and the sensitivity is ajustable. We took the signal from the LED array and connected it to an analog pin of an atmega328 (be careful with the voltage differences!)
This amplifier is also used in the so called LED-ORGAN, for instance:
In this LED ORGAN the signal is divided into three parts, HIGH, MID, LOW, using simple electronic parts.
Here is the Velleman Kit assembled:
An electret microphine has a minus and plus side: the minus can be recognized looking for connections to the outer metal.
But then came the students, and they wanted to be real men – in fact they are real men, but real men without any soldering experience-….
They bought an electret mic and we had to come up with the rest. Well, first we showed them the MIT hello.mic.45 scheme and labels.
Of course this is a very simple way to register sound, and it works but only with very very loud brutal sounds.
So we searched for new information. This can be found everywhere, but the posts are always describing one possibility. We wanted to compare.
We already bought an op-amp, LM 324 = CA 324, with four op-amps in one IC.
http://www.conrad.nl/, order number 175838
But how does an op-amp function, what are the principles?
This is explained nicely here:
But then you know about the principles, but as always electronics is about details, a small capacitor here and there….
So we found useful practical information (as usual) at sparkfun.com
They have a break out board: op-amp and are so kind to show the schematics. There is a lot to learn from that!
(You need a lot of 10K resistors!)
But also they have a break out board for an electret mic with an op-amp, and the schematics. Indeed they have two versions. One is obsolete and the other apparently their favorite.
First we made the op-amp which is an amplifier with two stages on a test PCB, using only one half of the chip (with 4 op-amps). It didn’t work, because we had the capacitors before the minus – inputs the wrong way around….this was better on the breadboard, where we could experiment before soldering.
So we made the mic-op-amp on a breadboard. This was useful, because changing the capacitor C3 can make quite a difference.
As you know from the principles the quotient R5/R4 gives the amplification, you can experiment a little bit with that too.
This op-amp is indeed amplifying, but this electret is a closed one, (one tiny hole in the middle) and may be because of that, the response is still not what we expected. We used Serproxy and Flash (with socket connection) to make a graphical representation of the signals, which shows a lot of details. Indeed it shows the loading and discharging of capacitor C1.
Changing the C1 makes a lot of difference too, making a wild noise around the average signal (500) tame.
We have to fiddle around a little bit further, looking at different electrets in combination with the op-amp configurations.
In the end we have explored three/four possibilities:
- the velleman kit, very well functioning, only 9V, can this work on a lower voltage too, with less LED’s… a test is needed?
- The electronicpeasant .com – LED organ (running at 5V), this works well with the first two amp – stages (2 transistors and the rest), picture coming up soon!
- the MIT solution, this works, but is very rough
- the op-amp, this requires lots of 10K’s (to start with), two amp stages,
- the op-amp electret combined, one amp stage
The op-amps ask for learning, comprehension and a bit of patience. The MIT board is not what we are looking for.
So my advice is: when you start experimenting and soldering, start with to the Velleman kit!
Then try out the LED ORGAN, take the first two stages, top left of the diagram.
If you have time and want to learn something, try the op-amps.