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This is a selection of small self-contained alarm circuits. They have a very low standby current; and are suitable for battery operation. Some are triggered by normally-open and normally-closed switches. Some react to changes in light or temperature. The result is a variety of output times and patterns.... [read more]

This is a single channel (on / off) universal switch that may be used with any Infra Red remote control that uses wavelengths between 850-950nm.... [read more]

Readers who do not care to modify the power supply of an old PC into a suitable halogen power source (see our April 2006 issue), may find the present design a welcome alternative. The circuit does not need any changes to the power supply. It allows the halogen lamps to be initially powered from the 5V rail of the supply via RE2, so that they are preheated. Subsequently, they are powered from the 12-V rail via RE1, while at the same time the 5-V rail is disconnected.... [read more]

This circuit provides a visual 9 second delay using a 7 segment digital readout LED. When the switch is closed, the CD4010 up/down counter is preset to 9 and the 555 timer is disabled with the output held high.... [read more]

Don't get caught with a flat battery; this easy-to-build circuit can cut off the power to a 12V fridge or car stereo system if the battery voltages drops below critical level. Electric fridges in vans and 4WDs are a great idea but if you are not careful, they can severely discharge the battery and leave you stranded. Maybe the battery will end up with severe damage as well. The same problem applies if you have a big stereo system and you like to play it without the motor running.... [read more]

This little circuit can be used to dim lights up to about 350 watts. It uses a simple, standard TRIAC circuit that, in my expirience, generates very little heat. Please note that this circuit cannot be used with fluorescent lights.... [read more]