|The unfinished clock without the arms|
The mechanism inside the clock runs from one AA battery and has a small buzzer that looks like a piezo. The positive side of the battery is connected directly to the buzzer by a wire. The other side of the buzzer is connected to a chip under an epoxy blob that switches the buzzer on and off. The 1.5v of the AA battery is not enough to run the MSP430 I am using so I wired in two AAA batteries. The clock case has just enough room for the extra batteries and a small piece of protoboard for the microcontroller. I opened the mechanism to solder in some wires so that the microcontroller can monitor the line switching the buzzer and drive the buzzer directly instead. One of the small gears inside quickly melted from the heat given off by the soldering iron a few inches away. Luckily, all of the local clocks use a similar mechanism and I replaced the whole thing for about $1. The wires from the mechanism are connected to a switch so that the buzzer can either be run by the microcontroller or by the original clock in case the extra batteries die. Another feature the clock is missing is a light, so I wired in an RGB LED I bought a few years ago. It has a light so that it can be used as a backlight but it also flashes colors in time with the music when the alarm goes off.
At first I tried soldering components directly to a DIP socket but this was surprisingly difficult, so I added everything to a small piece of left of protoboard. The AAA batteries are too big to fit in the clock case side by side so I couldn't use a battery holder. Instead I soldered wires directly to the batteries. This will make them hard to change but hopefully the MSP430 will use very little power waiting for the alarm to go off. Once I got everything soldered, the microcontroller would play the music it should but it would not stop playing even when it was disconnected from the line switching the signal. This is a problem I still have not figured out but I'm sure it has something to do with fluctuating signals in the circuit.
There are still a lot of bugs to be worked out but I hope to make progress soon and finish this little project quickly.