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Smoke Alarm Battery Life Extender
While smoke alarms are quite cheap devices, the cost of 9V batteries quickly exceeds their purchase price. Added to that is the irritation of random beeps from the alarm as the battery reaches the end of its useful life. This circuit allows typical smoke alarms to be powered from the 12V supply in a burglar alarm while still keeping the standard 9V batteries in place. It extends the 9V battery life to that of its "shelf life" as the battery is only required to drive the smoke alarm in the event the 12V supply is removed or shorted out....
The ICL7107 is a 3 1/2 digit LED A/D convertor. It contains an internal voltage reference, high isolation analog switches, sequential control logic, and the display drivers....
This circuit enables you to test quartz resonators at the range values from 32kHz to 24MHz. Confirmation of good state of quartz resonator is done by diode signalling LED and acoustic signal...
A dimmer is quite unusual in a caravan or on a boat. Here we describe how you can make one. So if you would like to be able to adjust the mood when you’re entertaining friends and acquaintances, then this circuit enables you to do so. Designing a dimmer for 12 V is tricky business. The dimmers you find in your home are designed to operate from an AC voltage and use this AC voltage as a fundamental characteristic for their operation. Because we now have to start with 12 V DC, we have to generate the AC voltage ourselves....