Design of Speed Sensor Unit :
The reed switch and a magnet need to be fixed on the front wheel of the motor bike. A small circular magnet (about 2 cm in diameter), normally used in speakers of small toys, can be used. Fix the magnet to the central drum of the wheel just below the spokes connected to the drum. Secure the magnet using hot glue or Araldite. For fixing the reed switch, a PVC pipe contraption needs to be made so that the magnet and reed switch are aligned. The materials required to build the contraption. Cut a 3.2cm diameter PVC pipe measuring 15.2 cm in length perpendicularly into two halves. Use only one half of the PVC pipe. Mount and secure the reed switch using Araldite and cable ties on the plastic handle (normally used in emergency lights). Once it dries up, solder two wires to the two oppositeend leads of the reed switch. Fix the plastic handle on the half cut PVC pipe using screws. Now, place the pipe on the front shock absorber fork such that reed switch faces towards the magnet. Connect a multimeter, set in continuity mode, to the two wires coming from the reed switch. Rotate the wheel slowly and see whether the reed switch closes when the magnet passes across it. If it does, the multimeter will give a continuity beep. When the magnet moves away from the reed switch, the beep will stop, indicating that the reed switch is open. Make a few trials to find the optimal position for mounting and fixing the PVC pipe such that the reed switch works smoothly. Mark the location on the front shock-absorber fork. Now you can fix the PVC pipe contraption to the shock-absorber fork using hot glue. Use liberal amount of hot glue to secure it to the pipe. Carefully route the two wires up to the bike’s handle bar using cable ties to secure the wire. This completes the sensor mounting part.