The electronic speedometer consists of a speed sensor, a signal processing circuit, a speedometer and an odometer.

Working principle of electronic speedometer

The speedometer sensor is installed in the instrument cluster and driven by the transmission through the flexible shaft. When the car is running, it will produce a signal proportional to the speed. It consists of a reed switch with one or several pairs of contacts and a rotor.

Signal processing

The signal processing circuit consists of a monostable trigger circuit, a constant current circuit, a 64 frequency division circuit, a power amplification circuit and a power adjustment circuit.

When the car is running, it converts the pulse signal input by the speed sensor into a current signal after shaping, and drives the speedometer to indicate the speed after amplification; At the same time, it also converts the pulse signal into a pulse signal with a certain frequency through frequency division and power amplification, so as to drive the shaft of the odometer stepping motor to rotate and record the mileage of the car.

The speedometer uses a magnetoelectric ammeter as an indicator. When the car runs at different speeds, the signal processing circuit converts the pulse signal input by the speed sensor into a current signal proportional to the speed, which deflects the ammeter pointer and indicates the corresponding speed.

odometer

The odometer consists of a stepping motor, a six-digit decimal counter and an internal transmission gear.

When the vehicle is running, the pulse signal output by the speed sensor is converted into a pulse signal with a certain frequency after frequency division and power amplification by the signal processing circuit, which acts on the electromagnetic coil of the stepping motor. The stepping motor converts this pulse signal into an angular displacement signal, which makes the motor shaft rotate and drives the six counting wheels of the decimal counter of the odometer to rotate in turn to record the total mileage and one-way mileage of the car. When it is necessary to eliminate short-distance mileage, just press the reset lever and the short-distance odometer will return to zero.