This switched ON bike lamp circuit was primarily intended to permit automatic switch-on of push-bike lights when it gets dark. Naturally, it might be applied for any other purpose involving one or more lamps to be switched on and off depending of light intensity. Power could be supplied by any kind of battery suitable to be fitted in your bike and having a voltage within the 3 to 6 Volts range. The Photo resistor R1 needs to be fitted into the box containing the total circuit, but a hole should be created in a convenient side of the box to allow the light hitting the sensor. Trim R2 until the desired switching threshold is reached. The setup will require some experimenting, but it ought to not be hard.
| R1 = Photo resistor (any type) R2 = 22K 1/2W Trimmer Cermet or Carbon type R3 = 1K R4 = 2K7 R5 = 330R * R6 = 1R5 * | D1 = 1N4148Q1 = BC547 Q2 = BD438 LP1 = Filament Lamp(s) * SW1 = SPST Toggle or Slider Switch B1 = 6V or 3V Battery * |
Bike Lamp circuit notes:
- In this circuit, the maximum electric current and voltage delivered to the lamp(s) are limited primarily by R6 (that can’t be omitted if a clean and reliable switching is expected). Consequently, the Ohm’s Law should be applied to calculate the ideal voltage and current values of the bulbs.
- At 3V supply, R6 value may be lowered to 1 or 0.five Ohm and the operating voltage of the bulbs should be chosen accordingly, by applying the Ohm’s Law. Example: Supply voltage = 3V, R6 = 1R, total current drawing 600mA. Decide on 2.2V bulbs as the voltage drop caused by R6 will probably be 0.6V.
- At 3V supply, R5 value should be changed to 100R.
- As an example: at 6V supply, one or much more 6V bulbs having a total current drawing of 500mA can be applied, but for a total current drawing of 1A, 4.5V bulbs need to be chosen, as the voltage drop across R6 will become 1.5V. In this case, R6 should be a 2W type.
- Stand-by current is much less than 500µA, provided R2 value following trimming is set at about 5K or greater: for that reason, the power switch SW1 could be omitted. If R2 value is set below 5K the stand-by current will enhance substantially.
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