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Tuesday, February 5, 2008

Count Down Timer

Timer kits are an ever popular item with the hobbyist. One of the main methods used is the ever-popular 555 timer IC. In this circuit we use a 555, a counter IC and a transistor switch to activate a relay either on-to-off or off-to-on (mode selected by a jumper) as soon as the counting period is over. Let us look at the kit in more detail. The circuit consists of 3 parts: an oscillator, a ripple counter and two switching transistors.

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