This experiment detects the presence of light. A photo-darlington transistor is connected to the circuit via a plug and socket and exposed to light. The change in resistance of the photo-darlington transistor creates a voltage change across it and this is amplified by the circuit and delivered to an input of the microcontroller. The program turns on the 8 LEDs when the photo-darlington transistor detects change in illumination. The photo-darlington transistor is connected to the circuit via a capacitor and only CHANGES in illumination are detected.
If the illumination is decreased, a point will be obtained where the circuit is sensitive to the changes in supply rail voltage. At this point the circuit will start to oscillate or MOTOR-BOAT. The circuit must be re-designed to prevent this from occurring. If the photo-darlington transistor is placed in a room with incandescent lighting, the 50 or 60Hz from the light will be detected. These pulses must be dealt with by the program to obtain a reliable HIGH/LOW pulse.
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