This is a new version of my Tengu clone. This time on a printed circuit board (PCB). I have them produced by Olimex and I am very pleased with the quality. The PCB worked on the first try and has some minor issues only.
Christmas is coming closer, so here is my contribution to put you in the right mood.
It is a blog hitcounter, that rings a bell. Literally. It puts a smile on your face, every time someone hits your blog. And it is a great way to annoy your colleages or your girl friend.
It consists of an Arduino board, a bell, a servo and a couple of lines of code in c, python and php.
When I first saw Crispin Jones Tengu, I was sure, I must have one. If you don’t know tengu and don’t want to follow the link, it’s a small face, made of LEDs, that reacts to music and sound.
It did not take long until I decided to clone this funny little device. All it needs is a microcontroller, an LED matrix and a sound sensor.
I searched the web for a cheap method to let the ATmega respond to sound. My knowledge in analog circuits is very limited, but what I do remember, is that you can not attach a electret mircophone to a controller pin. The signal of the microphone is just too small and has to be amplified. There is much of information out there, especially on diy amplifiers. I stumbled upon this little circuit here. It consists only of a handful of components:
Prototyping the amplifier
Putting things together on a breadboard.
Actually I had no 2N3904 around, so I replaced it with a BC337. The circuit is a emitter circuit with voltage degeneration (I dont know if that exists in english). I dropped the couple capacitor and took the signal right away at the collector.
Prototyping with the ATmega
The sound sensing is done with the ADC of the ATmega. A simple program reads the analog value of the amplifier over and over. If the value (loudness) exeeds a specific level, an LED is lit.
The schematic for rebuilding.
The code can be found here mic_sensor.c. It is just hacked together and has lots of room for improvements.
Video
Here is a video that I made. Has lousy quality, for both, video and audio.
Conclusion
It was easy and worked pretty well. I enjoyed looking at the LED responding to the music. I haven’t recorded anything with this amplifier, it might sound awfull. Next steps could be playing the sound back or be able to analyze the sound (FFT). And (re-)learning more on analog circuit design.
Links
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