Adding Volume Control to a Cheap Alarm Clock

In the boarding school where I study, we get these very simple, low-cost alarm clocks. They're quite loud, and can be very irritating to wake up to. This Instructable is about how I used a potentiometer (a variable resistor) to allow volume control.

A potentiometer

This step may vary from clock to clock, though there may be some similarities. With my clock, I had to unscrew the purple frame, pull off the clock hands and then pull off the clock face to reach the rest of the internals. My clock face was held down with a small piece of double-sided tape near its center, so nothing got damaged when I removed it.

Connecting the potentiometer between the buzzer and the rest of the circuit was pretty straightforward, as my clock had an ample amount of wire between the buzzer and the rest of the circuit. This will likely be the case with many similar low-cost clocks. I did not take a picture of the clock internals without the potentiometer, but you can get an idea from the attached picture -- each of the wires from the buzzer was about as long as the yellow line drawn.

The potentiometer has to be connected by the middle contact and one of the side contacts. Which side contact you choose will determine which way you have to turn the knob to increase/decrease the volume. The lowest resistance of the potentiometer will correspond with the highest volume setting. Consider this while connecting the potentiometer. The first time I connected mine, I connected it in the direction opposite to what I had intended.

For reference: In the picture, the three arrows point to the three potentiometer contacts, and the two red arrows point to the contacts I used. With this configuration, the potentiometer has least resistance when the knob is turned fully anticlockwise (clockwise when viewed from the outside of the clock).

The way this works is as follows. When a resistor is put in series with the buzzer, the total resistance of the circuit increases, decreasing current flowing through the circuit. When current flowing through the buzzer decreases, its volume decreases. This is why the highest resistance value corresponds to the lowest volume of the alarm.

Finding space to mount the potentiometer wasn't a problem with my clock, and will likely not be a problem with most cheap alarm clocks of this kind. There was plenty of free space on the back of the clock's body, so I drilled a hole in the back to mount the potentiometer.

That's it! Now all that I had to do was to reassemble and use it. I put a spot of glue in place of the double-sided tape to hold down the clock face.