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.
p/s: ni belom consult lg dgn sir. tp da mule working on it. moga2 dipermudahkan. amin
please proceed
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