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Introduction:
This is my first real Arduino project.  It comes after building a handful of Picaxe projects over several years.  Both platforms are nice, but all things being equal, the Arduino is more open and hence, offers more freedom.  I'm sure that there are some good comparisons of these devices on the net, but since you're already here, you can read my impression of the differences.

Description:
This is a simple sequencer machine which uses Capacitative Sensing Code for input to the Arduino.  It is is a combination drumpad and sequencer.  It has just two modes, record, and playback, and needs very few components; an Arduino (of course), and just 3 resistors and a piezo speaker.  If you're feeling decadent, you can add an LED (with a resistor) for more "ooomph".

I have a $5 version of this which runs on a PICAXE microcontroller.  As you can see from the project enhancements, moving
to an Arduino is a nice change since it offers much more potential with far faster processing, much more memory, and a nice
variant of C which is closer to the high-level object oriented languages that I like.  But I can't give up on the Picaxe either. 
It offers unparalled simplicity, lower cost, and lower power requirements.  In fact, my picaxe projects never needed a power-switch since they could go to sleep and wake up entirely under software control.  It is just a matter of time before this level of
power conservation comes to the Arduino, but its not quite a nanowatt microcontroller yet.


Basic function:
When the program starts, it expects the sensing buttons to be untouched, and needs a fraction of a second to calibrate a good
value to distinguish between touched and untouched.  It then beeps a high pitch beep to indicate the start of the record sequence.
 
 At this pont, the user taps a rhythm on any of the 3 pads:  low, medium, and high pitch tones.  When finished, tap one final time
 to indicate when the drum-loop should repeat. 
 
 After the recording is finished, the Arduino removes the trailing silences, and applies a modified median filter to clean up the
 recorded track.  Capacitive sensing buttons have noise like you wouldn't believe, making real-time input a bit challenging. 
 Then playback looping begins.  Your track is repeated ad infinitum, in all its glory.  Touching one of the buttons at the end of
 a loop resets the device and enters record mode. 
 
This program contains some good generic code.  The capacitive sensor routines senses a finger touching a wire attached to a pin. 
It needs only a 1M ohm resistor, so using this as a UI is cheaper and easier than buying buttons!  And Paul Badgers tone generation
routine is essential knowledge for those who wish to beep.

My capacitive sensing code is based on Paul Badgers code, but should be easier to read since I don't know the Arduino particularly well! 

I wouldn't have used his routines, but using external libraries with the Arduino software is kind of a hassle.  I like very
portable code, and will stick with my stand-alone routines until the Arduino IDE has a mechanism for importing external libraries nicely.
The IDE is ok, but compared to OOP methods using Netbeans and Java, embedded programming still has a little way to go.

Power is supplied by a wall wart through the onboard Arduino voltage regulator, or through the USB bus if you have the programming header connected. 

Assembly:

The schematic of this project is pretty darn simple.  I first assembled it on a prototype.  Its worth having a a dedicated Arduino on a solderless breadboard so you can quickly wire-up anything you wish.  I then mounted it in a craft box that was predecordated with tissue-paper and pictures.  The RBBB Arduino just fits inside.  3 small sheet metal screws stick out of the front of the box and provide the touch pad surface on which the user taps.  There's also an LED.  This was of the clear variety which was difficult to see, so I roughed it up with sandpaper which converts it nicely to a diffuse LED. 

The software is fairly straightforward. Since I worked out the interface previously, it was pretty easy to code up.  And after programming on a Picaxe for a while, the richness of the Arduino makes you wonder if there is anything that you can't do. 

This code is explicitly released under the GPL. And this page is licensed under a Creative Commons Attribution 2.5 License.  

Write me if you find this project interesting. Link to this page if you find it relevant.

Warning, warmly greet new renewably powered interactive autonomous electromechanical overlords. This project is provided without any warranty and probably isn't suitable for anything.

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