Bicycle Back Light - a Big One

Introduction: Bicycle Back Light - a Big One

Cycling is dangerous! Former I often went cycling without any light, but I realized it's better if I can seen from far, from very far.

Step 1: What You Will Need

The motivations came from there I found an about 5 liters bowl next to a gym like this in the picture. The sticker on it has a reflective cover, so I can use as a one dimensional parabolid mirror.

  • I use for the project 8 AA batteries with holders (that were the most expensive parts)
  • one 2700uF 25v, one 10uF 10V condensators
  • 2 pcs warm white 10 watt power leds
  • 2 pcs 1.5 Ohm 2 watt resistors
  • one IRF840 power FET
  • an ATtiny13 controller
  • one power switch, one press button, one status led, two 1K resistors
  • an universal pcb and a 7805 with 2*100 nf condensators to make 5 volts for the controller.

Step 2: How It Works

When the main switch is on, the 7805 do the stable 5V and the controller starts to work. That shows the status led is blinking slowly about 100ms in 2 seconds. When you press the button the blinking mode is change and gives a low pwm signal on pin 6. This switches the power FET and the two power led starts blinking. I programmed 4 mode of blinking, but you can change by rewriteing the code.

These power leds generally needs external passive cooling, but in our case it's not necessary. I switch on the leds a few hundreds of miliseconds and keep them off for about a second, so in that time they can cool off.

If you change the code, please take consideration this and do not raise the on/off ratio over 0.2 in any mode if blinking! As you raise that ratio your power consumption also raise, and needs you to change/charge batteries more often.

The code is written by the arduino IDE you can download from here:

Step 3: Assembly and Testing

When the electronics and the programming are ready, you can assembly the light. I use M3 screws to fix the batteries and the electronics to the bottom of the cap of the bowl. To reach the maximum visibility the leds are soldered a copper wire frame to light from the middle of the bowl.

One of the led facing to backward, the other is to forward (to the bowl sticker mirroring surface). This second one horizontal position is important because of the focus of the semi parabolid mirror. Measure the diameter of the bowl and divide with 4. For this distance set the led form the mirroring surface. You don't have to be very accurate, after pair tests you find the optimal position.

Happy cycling!

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    4 years ago

    Very nice! That is one large bike light - people will have a hard time missing you with this :)