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AVR Light Controller for LiPo or LiIon-Powered Halogen Bike Lights

AVR Light Controller for LiPo or LiIon-Powered Halogen Bike Lights

This project is about building a power controller based on a small microcontroller, here the ATtiny45 was used. The desired output power can be achieved using Pulse-Width Modulation (PWM) of a power source LiPo battery in this case .The duty cycle of the PWM determines the amount of power sent to a load that is the halogen light.
The resulting effective power of the halogen light is calculated by integrating the applied power over time. With on/off modulation, this results in:

duty cycle = Veff2 / Vbat2

In this project, a microcontroller continuously measures the battery voltage level and calculates the duty cycle to achieve a desired output power.

Beside controlling the output power, the use of a microcontroller allows for other goodies:

Smooth transition between power levels.
A remote control with a single button and an LED that can be attached for example to the strap of a bike pack.
The button on the remote allows to turn the light on. It further allows to toggle between BRIGHT and DIMMED power mode. Holding the button for a second turns the light off.
The control LED warns about low battery or when the light is not connected. Also, holding the input button when the light is off triggers the LED to show the battery voltage level.

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