Problem Corner

A guide to troubleshooting MadLab kits.

If you have any questions about your MadLab kits please send your letters to: MadLab, Unit 7, Abbeymount Techbase, 2 Easter Road, Edinburgh EH7 5AN, U.K.

Or, email your questions to: info@madlab.org

"Mad Music Machine tunes playing too fast"
"Howling SuperSpy"
"How long does a battery last"

Dear MadLab,
When I touch the back of my Mad Music Machine the tunes play much faster. Is something wrong?

Your Mad Music Machine contains a computer chip which has a master clock controlling the speed of the program. The clock uses a capacitor, and when you touch the board your body changes the capacitance. This happens because your fingers bridge across the legs of the capacitor and this increases the speed of the clock. Thus the chip runs faster and the music plays quicker.

Dear MadLab,
My SuperSpy makes a high pitched howling noise when I place the microphone next to the earpiece. Why is this?

Firstly, there is nothing wrong with your SuperSpy. In fact it's a good way of testing that a SuperSpy is working. The technical name for the whistling sound is acoustic feedback. It is caused by tiny vibrations which rapidly grow bigger and bigger as they are amplified and fed back to the input via the earpiece.

Dear MadLab,
How long will the battery for my Flashing Lights last? Can I make it last longer?

The Flashing Lights circuit draws about 20mA on a fresh battery. An ordinary zinc chloride battery should last up to 3 days and an alkaline battery twice as long. It's difficult to calculate the exact time because the circuit will work down to 3 volts where the current drawn is only 5mA.

To make the circuit more energy efficient you can use ultrabright LEDs in place of normal LEDs. Change R1 & R4 to 4k7, R2 & R3 to 220k, and C1 & C2 to 1uF. The lights will flash in exactly the same way as before and will be just as bright but they will use only 1.6mA and the battery will last more than 10 times longer.