POV Clock
March 2008
For my ME 135 design class, two friends and I chose to build a POV clock. It turned out to be a very fun and educational endeavor. I had seen several examples and knew that the concept was fairly simple, but as with most ideas, implementation is the hardest part. I have included a simple explanation of the clock, a short vido clip, and the raw code in case you are one of those people who like to read C.
POV stands for persistence of vision. The human eye refreshes at a relatively slow rate, causing the brain to see images for longer than they may actually be present in front of your eye. Thus, an LED which blinks at a rate of 100 Hz will not appear to be blinking, but instead will look like a steady light. The POV clock works off this principle by quickly rotating an array of LEDs and blinking each LED at just the right time, so that after a complete rotation, your eye sees a basic analog clock.
For this project I used the eZ MSP 430 F2013 microprocessor from TI. It turned out to be a fantastic choice. It features a clean proprietary coding interface from TI, a hassle free USB connection, a very small footprint, and extremely low power consumption. The C code that runs the clock is interrupt driven, modifying the “time” array every second, and flashing the appropriate LEDs during each rotation. The clock also accounts for rotational velocity changes by timing each loop with the aid of the infrared emitter and detector pictured to the left. This simple setup prevents clock drift.
In case you want to look at the C code to see what was happening behind the scenes, I have included the file here:
pov_c_code.rtf | |
File Size: | 12 kb |
File Type: | rtf |