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Automatic Bike Headlight Switch

2015-03-01 14:48  
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Automatic Bike Headlight Switch
Improved bike headlight switch circuit presented here has been designed to switch bike headlight on (or similar loads) at a presettable ambient light level. The circuit is based on the renowned timer chip LM555 (IC1), here triggered by a decrement in ambient light level. Here is a 220V automatic light switch, just in case you need one. Bike Headlight Switch Notes The whole circuit should be powered from the 12V bike battery Slight intervention in the existing electrical wiring of the vehicle may become necessary to add this circuit Use of a medium-size encased LDR is recommended for reliable operation. Fit the LDR at the front side of the bike in an appropriate position The relay used in the prototype draws near 37.5 mA. 555 IC output can switch up to 100mA, which is adequate for driving the relay 555 IC will only rise to near 10v for the 12V input supply and the diode D1 will drop 0.7Volt. As a result the 12V relay will only get about 9.3Volt. However, pick-up voltage of a standard 12V relay is 9V, this is not a problem. D1 is added intentionally to avoid episodic timer latch up