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Friday, October 9, 2009

Sun Up Alarm Circuit

This circuit can be used to provide a audible alarm for when the sun comes up or it can be used in a dark area and detect when a light comes on. It can also be used to detect a light beam, headlights etc. This circuit is a simple design circuit for alarm. This is the figure of the circuit.


The circuit works as follows. The photo transistor is very sensitive to light. (Any phototransistor will work fine) The sun shining on this device will provide a high to one of the NAND gates. This will cause another NAND gate to oscillate which will drive another gate to output a 100hz tone. The transistor provides drive for the speaker.

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