Auto LED Taillight for a Bike

This is a circuit for automatically switching off and LED taillight for a bike. The backlight turns on by movement (in the dark). After about 20 minutes of inactivity, the backlight is switched off again. So you cannot forget to turn off the backlight so that you are less likely surprised by batteries. 

Auto LED Taillight Circuit Diagram

Auto LED Circuit Diagram

S1 is a motion switch. When the switch closes C1 is charged. Therefore FET switches T1 and burn the LED. T1 can however only enabled when R3 is sufficiently high resistance, or when it is dark. R1 C1 discharge slowly so that after about 20 minutes the FET turns off and the LED goes out.

The circuit may be built into the housing of a rear light on the battery that is inexpensive to buy in the market. That way you already have a beautiful body.

Parts List:

     R1 = 2.2 MΩ
     R2 = 2,2 kohm
     R3 = LDR
     R4 = 220 K?
     R5 = 22 K?
     R6 = 220 Ω
     C1 = 100 V μF/16
     D1 = high intensity LED 5mm red
     T1 = BS170
     S1 = motion switch (eg RS No. 455-3671)
     S2 = switch

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