What is POV?

POV stands for Persistence Of Vision. It’s a term that's been applied to devices that rely on the eye's tendency to continue to "see" an image for a short time after it has disappered. This is also what causes the apparent blurring of objects that are in motion (like an airplane propeller).

This project consists of three circuit boards with a row of 32 LEDs on each (actually 64 LEDs because they’re double sided). The circuit boards are mounted radially in the spokes of a bicycle wheel and batteries near the hub supply power to them. The LEDs are controlled by a microcontroller that measures the rotational speed of the wheel by way of a hall effect (magnetic) sensor. As the wheel rotates, the microcontroller turns the individual LEDs on and off in such a way that a static image appears to float inside the wheel.

Although the hardware and firmware are probably different, this project was inspired by Lady Ada’s Spoke POV.

Improvements in version 3:

In version 3, I made the following improvements over version 1:

• By running the front / back LED pairs in series instead of parallel, it now uses half as much power as version 1, yet the LEDs remain equally bright.
• By using the STP16C596 constant current LED driver instead of shift registers, the design is simplified, component count is reduced and it’s easier to build.
• The firmware shuts the circuit down automatically when the voltage gets too low to prevent damage to rechargeable battery packs.
• Switched to a low dropout regulator which gives more reliable operation when the batteries are almost depleted.
• Length of the board has been reduced slightly to fit most bike wheels that are 26" and larger.