This short collection of projects - some useful, some instructive, and some amusing - can be made for around 10 UK pounds (16 US dollars). The estimated cost does not include an enclosure (box). All of the projects are battery powered, so are safe to build.

A two-in-one design that will bring comfort and joy to your youngster’s room.

This design is intended as a battery-powered nightlight suitable for a child’s bedside. Its power requirements are low and it should run nightly for several months from a lantern-type 6V battery, such as the 908S. It will run for a similar length of time on four D-type cells in a battery holder.

The key to this economical circuit is that it does not stay on all night. It relies on the fact that a typical child drops off to sleep within 10 minutes or so of being “settled down”. The nightlight has two filament lamps, such as 6V torch lamps running at 100mA each. These both come on when a pushbutton switch is pressed. From then on, the lamps are under the control of timer circuits.

One of the lamps stays on for about six minutes, which is usually long enough for the child to fall asleep. However, the other lamp stays on for about 13 minutes. At that time it dims down gradually, to avoid plunging the child into total darkness.

The lamp-switching circuit is on a separate circuit board and can be controlled with a pushbutton switch as described above. However, the project also includes a second circuit board, which is optional. This is a sound-sensitive trigger. When its microphone detects a sound such as a handclap, a cry or a shout, or someone hits the bedside table, the circuit generates a low-going output pulse. This triggers the switching circuits to put on the lamps for another 6/13 minutes sequence.