Cycling is our common means of transport, if accompanied by a bicycle speedometer, you will be able to master cycling speed, especially for cyclists , the usual training, a
reasonable allocation of the way the speed, rhythm master speed, is a good method, bicycle speedometer circuit shown in Figure 5-33 below. The speedometer use bike ride line speed rotation of the wheel is proportional to the relationship between the frequency of rotation of the wheels is converted into a linear DC voltage ripple voltage and remove it from the electrical voltage meter displays the voltage value corresponding to the riding speed. When riding infrared light detector per revolution of the wheel when moving hair a week, the next pulse, the crystal tube VT2 conduction generates a pulse to the next hop single trigger group consisting of an integrated circuit 555 -shot circuit. Riding faster time two pulses of infrared light emitted by the detector is shortened to increase the number of one-shot circuit outputs a high level, the average value of the DC voltage meter indication. Meter scale in speed unit km / h, said the number of rotations of the bicycle wheel can be calculated based on the wheel circumference obtained, currently used bike 71cm (28in), 66cm (26in), 60cm (24in), 50cm (20in) 4 class , given the scale that is four available. 28in bike to calculate, such as when 40km / h speed line Chi, the wheels turning about 2.5 times / s. Forgiving one-shot timing resistor RP1 and capacitance values can be used iookfl c2 and o. 47vF. Bicycle speedometer, the infrared light detector can be used for any infrared tube, LED and VT1 mounted on special brackets, the stent with a thin metal plate from a cross-sectional shape can refer lock structure and mount the front bicycle wheel spokes tops an obstruction, so that each revolution of the wheel, red light detector is shielded from the outside once. Transistor VT2 silicon NPN transistor 9014, selected about 120 betas. When the base integrated circuit NE555. Potentiometer RP1, RP2. They are made WH7 type trimmer potentiometers, remaining resistors are used RTX type 1 / 8W carbon film resistors. Header with 91C2 type. Remaining capacitors are used CJ11 metallized paper dielectric capacitor.