Adjustable 1-10 Minute Timer Project

The circuit starts timing when switched on. The green LED lights to show that timing is in progress. When the time period is over the green LED turns off, the red LED turns on and the bleeper sounds. The time period is set by adjusting the variable resistor. It can be adjusted from 1 to 10 minutes (approximately) with the parts shown in the diagra

m. You can mark the times on a scale drawn on the box. Please note that the range of time periods is only approximate. With perfect components the maximum time period should be 4 ½ minutes, but this is typically extended to about 10 minutes because the 220 µF timing capacitor slowly leaks charge. This is a problem with all electrolytic capacitors, but some leak more than others. In addition the actual value of electrolytic capacitors can vary by as much as ±30% of their rated value.

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