I did this a little while ago, so sorry for not posting earlier. My chronology is all messed up. ; )
So, I play piano in a salsa band at MSU, and it is my favorite thing to do. In learning about how to play the music and what this whole other world of rhythm was all about, I learned about Clave: the rhythm, the instrument and the word. I got one, I learned that it is tricky for me, and that I needed more of it in my life, in addition to needing a steady clave rhythm to practice with.
So I made myself a new metronome.
This was a fun project for me. It has one of Paul Badgers' Bare Bones Boards inside, as well as a Minty Amp kit, some buttons for changing the tempo, adding mambo bell and cascara and changing back and forth between son and rhumba clave. I have had some practice with using switches, potentiometers and lights with and Arduino, but making them make sound and steady rhythms, and then amplifying it so that it's loud enough to practice with a piano required some learnin'.
To get the Arduino to make sound, I used one of the pins that was capable of Pulse Width Modulation (PWM) and used it as an Analog Output pin. The three sounds (one sound for clave, one for cascara and one for mambo bell) are each really fast pulse (or square) waves that are only played for a couple cycles (high frequency for a very short amount of time). The three different sounds are different frequencies and different lengths. The sound of connecting the Arduino directly to the speaker worked ok, but wasn't very loud, so I tried to amplify!
I still need to read more about Audio Amplifier chips, but this Minty Amps kit worked real well for amplifying my signal a little. Although, with regular audio, I'm pretty sure there's an impedance problem somewhere or something, because it was very distorted. I wanted to put in some potentiometers for different volume stages (one control for dropping the signal between the Arduino and the Amp, and one between the Amp and the speaker). However, I either wired the pots incorrectly or they're broken, so they just fizzle out in the middle. I put in two bybass switches, one for removing each of the pots from the signal chain.
Anyhow, I made it and I use it for practicing now, which is great, because this is one of my only projects that I actually use regularly. Total cost ~ $35