Programmable light controller

The main objective of this project is to design a maintenance free and low-cost light which automatically turns on and off at the predetermined time of the day.

To meet the above requirement I designed this controller using ATmega8 MCU and DS1307 RTC. The driver stage of this light controller is intended to work with commonly available 7W LED modules.

PCB of the programmable light controller.

The core component of this programmable light is ATmega8 low power CMOS microcontroller. The main reason to select this microcontroller is it’s lower cost and higher availability. Except for the above two reasons this microcontroller also bundled with a rich set of peripherals which including 23 GPIOs, 3 independent timers, Two-wire serial interface, EEPROM, etc.

Apart from ATmega8 microcontroller, this system uses DS1307 real time clock to maintain system time. Like ATmega8, DS1307 is also a very popular RTC in the market.

This controller is designed to work with a 24V DC power supply. The main reason to select 24V is that most of the medium power LED modules in the market are designed to work with that voltage. During my search all the medium power LED modules which I found are designed to work with 20V - 28V range. Out of those LED modules, the majority of modules are rated for 24V input.

The bottom side of the programmable light controller board.

For this circuit, the recommended power supply is 24V 1.5 A portable switch mode power supply. Except for the LED driver stage the all other parts of this light controller is designed to work with 5V. MC34063 DC-to-DC converter is used to supply 5V to those components.

To reduce the size of the PCB I design this system using surface-mounted components, but this system can also build using through-hole type components. At the prototype stages, I build this system entirely on a breadboard using through-hole type parts.

To build 7W light, I used LED lamp parts available in the market which including Warm white 7W LED panel, aluminum lamp shell (heatsink) and diffusing cap (lamp cover).

All the design files and source code related to this project are available at https://github.com/dilshan/programmable-light. The complete documentation of this project is also available at Github Wiki.

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