Sunrise Word Clock – Design

My next project is a word clock inspired by drj113’s instructible on making a word clock.

My design differs from drj113’s original considerably

Design Modifications:

• Rearranged lettering on the front, giving am and pm yet maintaining a compact design
• Dimmable LED channels so that i can create smooth time transitions
• Light sensor so that brightness can be adjusted according to ambient light
• Superbright power LEDs on the back so that the clock can be used for dawn simulation.

I’ve also decided the frame of the clock will be aluminium, touching this aluminium should toggle the power LEDs on and off (with smooth transition).

Overall Design:

As with my DIY bench power supply, I’ve designed my project in sketchup:

(download .skp)

The front is smoked perspex or glass. The power LEDs for the sunrise alarm will sit behind the clear plastic around the edge., using the aluminium frame as a heat sink. I’ve done a sketch of how the layers of the clock will fit together:

As the circuit board needs to be compact, i will be eventually make a surface mount PCB for it. My plan is to try and make this look professional as it will be visible through the perspex backing. I haven’t yet figured out how i’m going to build most of this, but want to get started anyway.

Potential Issues:

1. 23 separate LED channels that all need to be PWM controlled – possibly use 2 microcontrollers and communicate over I²C
2. Programmable time and alarm – set using buttons and LCD
3. accurate clock time – use dedicated clock chip with battery backup
4. touch sensitive aluminium frame – unsure
5. non-linear light sensor response – careful resistor choice and nonlinear software rule

I’ll come to each of these issues in time. All of these are things I’ve never approached before so it should be interesting.

I’m going to start by building the fundamental circuit on breadboard (microcontrollers, LCD, buttons, a few LEDs, light dependant resistor) and figuring out the code. After that i’ll solder a completed circuit on strip board and concentrate on building the word clock frame pictured above. Finally I’ll rebuild the circuit as a PCB

Any ideas or potential issues, feel free to comment.