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Using Bicycle Wheel to Display Text
The project shows rotating LEDs on a bicycle wheel that is capable of reading the RPM of the wheel and displaying the value with LEDs with fixed display scan rate for allowing smooth display at any rotating speed.
The PCB from an old project board was used since it contains an ATmega8 MCU, ULN2003, and 7 high-intensity red LEDs. The LEDs are controlled by Port D by writing a value on the port and using a busy loop while the MCU uses its internal clock circuit.A position sensor made from a relay coil has been added along with a magnet and an amplification circuit in order to display the pattern always at the same place. The magnet is fixed on the bicycle frame and the coil is inside the wheel. A small voltage is generated by the coil each time the magnet passes near the coil. This voltage is boosted by the amplification circuit to an acceptable level for the MCU. Making this work correctly would require a small code. The MCU will wait for a pulse, scans the picture one time and wait for another pulse, which displays the picture.