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This digital SP tachometer for bikes uses 2 reed switches to urge the speed data of the bicycle. The reed switches are put in close to the rim of the wheel where permanent magnets pass by. The permanent magnets are connected to the wheelspokes and activate the reed switches everytime they pass by it. The speed is digitally displayed. The tachometer circuit works in step with this principle; the pulses created by the reed contacts are counted inside an explicit time interval. The ensuing count is then displayed and represents the speed of the bike. 2 4026 ICs are used to count the pulses, decode the counter and management 2 7-segment LED show. RS flip-flops U3 and U4 perform as anti-bounce. The pulses arrive at the counter’s input through gate U7. The measuring amount is set by monostable multivibrator U5/U6 and might be adjusted through potentiometer P1 so the tacho are often calibrated. The circuit U1/U2 resets the counters. Electronic bicycle SP tachometer circuit diagram Since batte...

Anyone performing their own automobile tune-ups knows how important it is to know your engines speed. With this tachometer, you can measure your engines speed without any connections or annoying timing lights.      Wireless Auto Tachometer Circuit Diagram PC board layout and parts placement  Calibrate the unit as folows: Set up this circuit: Turn on the Tach and allow a few minutes for temperature stabilization. Set S2 to 4 cylinders and adjust R5 for a meter indication of 180 (1800 rpm). Set S2 to 6 cylinders and adjust R6 for a meter indication of 120 (1200 rpm). Set S2 to 8 cylinders and adjust R7 for a meter indication of 90 (900 rpm). To use the Tach, turn it on and let it sit for one minute to allow for temperature stabilization. Extend the antenna, select the right number of cylinders and hold the unit over the engine. If the reading is erratic or the needle jumps around, move the antenna closer to the ignition coil or spark plug wires. The unit draws power fr...