In-depth analysis of electronic speed display

This is a simple diagram of a tachometer. The basis of the frequency converter circuit is the current, which converts the input signal into a proportional current measuring pointer device. The deflection of the milliammeter is proportional to the frequency of the input signal. To install the device on the input pin A, the car should be connected to the high voltage line, and pin B- is connected to the mass of the vehicle.

To calibrate the tachometer circuit, set the engine trim pots R2 and R4 to the middle position. Turn on the power circuit and switch to an input rectangular pulse of 60Hz from any generator. Rotate resistor R2 to select the statement milliammeter equal to 0.36mA, equivalent to 3600./Min. Disconnect the input signal and trim R3 so that the instrument displays 0mA. Reconnect the input signal to 60Hz, and if the reading is different from 0.36mA, rotate R4. A fully calibrated speedometer should read 0mA at 0Hz input and 0.36mA at 60Hz.

Speed ​​display diagram Note:

I have not tested the tachometer? Schematic diagram of any car. Install it on the car, all responsibility you assume.

However, the signal from my function generator tachometer works fine.

The voltage at the high-voltage wire connector from the ignition coil reaches several thousand volts. The motor vehicle must be turned off when you connect the tachometer. If you do not have sufficient experience and knowledge of automotive electronics, do not install a tachometer in your car. I do not assume any responsibility for accidents that may happen to you.

For the power tachometer principle circuit, a 12V power supply is required.

The bridge rectifier D3 can be assembled from four diodes, all 1N4007.

M1 – milliammeter pointer, current full deflection 1mA.