Persistence of Vision (POV) can be used to display text and graphics on moving objects. For one of the Team Projects that I did, we had to make a POV display on a bicycle wheel using LEDs.
An ATmega 328P was used as the microcontroller for the project. 32 RGB LEDs were controlled via two 16-channel LED drivers and three FETS. The FETs were used to switch between which colour was displayed at any given time (red/green/blue).
An image had to be visible on the wheel between 60 and 200 RPM. In addition to this, an advanced mode was used to measure distance and speed.
We used a magnet mounted in a fixed position on the wheel supports and a hall effect sensor to measure the speed of the wheel to work out how quickly to change the colours on the LEDs.
My main contribution to the project was the PC software, the bootloader code and soldering/testing. The software was used to make custom images to display on the wheel and see what they would look like when the project was running. It also communicated with the AVR over USB to download data to it. The bootloader code was used to save an image (~11.5kB) onto the internal flash memory of the AVR. This removed the need for external EEPROM storage. My PC software code is available on Github (see the link to my Github account on the right).
Now for some pictures! First of all, the PCB:
Then we have some images of the project in action:
A more complex pattern: