Measure the distance by bicycle

Operation of the circuit. Wreath switch S1 to detect the magnetic field. By S1 on the circuit.When a magnetic force drew near.When the magnetic field out away.It works in conjunction with resistors R1, R2 and capacitor C1.Pulse generator signal to IC1 to count pulses. When the pulse count to 8, the voltage is “high” from the pin 6, through R4, to stimulate the base pin of the transistor Q1 to work.
The current flowing through the LED, in Photocoupler IC2 transfer pulse output signal to Pin 7, 8. Into a series of modules, the frequency of the measurement distance is already installed on the bike.

The magnets are mounted on the cage wheel spokes, the wheel is about 12.5 inches from the center.The switch S1 wreath mounted bicycle stand tall, to meet with a magnet. When the magnet rotates around with S1 which is fully fit, or the origin of the pulse signal is a pulse. If the wheel rotates a full eight rounds, will have a pulse input to IC1, 8 pulses. The pressure to stimulate the transistors work, and displays the distance of one meter. If the wheel rotates around 9, or pulses 9, enter the IC1 is a reset, or start counting again until 8 around to show off to measure the distance. A second time. Each time it is displayed to a distance of 0.01 miles, or about 16 meters.

Source: http://www.hqew.net/circuit-diagram/Measure-the-distance-by-bicycle_10864.html