universal tachometer signal interface

• 2021-12-30

In the automobile instrument panel, the engine tachometer and speedometer are two very important gauges. The tachometer collects the pulse of the engine speed sensor to indicate the current engine speed and reflect the working condition of the engine. The speedometer collects the pulse of the vehicle speed sensor to indicate the current vehicle speed and its changes. At present, vehicle modification is becoming more and more common. The modification of engine, gearbox and tire will cause the indication error of engine tachometer and speedometer. The inconsistent number of speed pulses before and after engine modification will cause the display error of tachometer, resulting in the failure of engine in time. The inconsistent pulse number or tire diameter of the speed sensor before and after the modification of the transmission or tire will cause the speedometer display error. Because it can not correctly reflect the current speed, it is difficult to reach the economic speed per hour. At the same time, it can not be found in time when there is overspeed.

The signal converter includes pulse input interface, pulse output interface and parameter configuration interface. Its hardware circuit mainly includes four parts: pulse acquisition circuit with adjustable filter frequency, pulse output circuit, RS232 serial port communication circuit and LED indication circuit. RS232 serial port communication realizes parameter configuration, and LED indicates whether the converter has downloaded parameters.

In the design of pulse acquisition circuit, firstly, the signal of speed / vehicle speed sensor is converted to TTL level through shaping circuit, then the burr on the pulse is removed through RC low-pass filter circuit, and the input capture pin of MCU is introduced. The digital potentiometer with fixed capacitance and adjustable resistance is used in the low-pass filter circuit. When the number of sensor pulses changes, the low-pass cut-off frequency is adjusted by the digital potentiometer to realize the programmable adaptive pulse acquisition of low-pass filter threshold, so as to ensure the universality of the converter.

The signal converter realizes the frequency conversion of engine speed pulse and vehicle speed pulse before and after modification, so that the original instrument continues to display engine speed and vehicle speed information accurately and in real time. Download the parameter configuration before and after refitting by means of serial port communication, adjust the low-pass cut-off frequency of speed and vehicle speed pulse acquisition circuit through digital potentiometer according to the parameter configuration, and carry out corresponding frequency conversion. By downloading different configurations and low-pass cut-off frequency adjustable acquisition circuit, the universality of the converter is ensured, which has wide applicability and strong practical value.