Project 9: Solar Motion Detector / Beam Break Detector
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Required parts: Solar cell, microcontroller (|jC), 2x 4K7 resistor (yellow, purple, red, gold), 470 ohm resistor, (yellow, purple, brown, gold), 2V4 zener diode, piezo sounder, wire.
How it works: The solar cell provides the supply vo tage for the microcontroller. Once the controller receives 2VDC it storts running its internai program The zener diode and the 470 ohm resistor make sure the supply voltage of the controller ne ver g ces beyond 2.4V, even in bright sunlight. A too high voltage can damage the devise. T'ie vc :a;e generatec1 ::y the solar cell is also divided by two by means of two equol resistors (4K7) and fed to the analog irput of t'ie controller.
Even in brght surlght. the nput receives no more than 4.5/2 = 2.25VDC. The internal software measures' the voltage at the input and compares it to the previous level. When it detects a sudden change ( .e. when the beam is interrupted or someone casts a shadow on the solar celI ). it generates a sound trough the piezo.