Electronic tachometer for a car. Free Technical Library article

Free technical library

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Schemes of radio-electronic and electrical devices

Electronic tachometer for car

Free technical library

Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices

Comments on the article

It is sometimes interesting for the driver to know how many revolutions the car engine develops. This can be determined using a simple electronic tachometer (Fig. 1), the measuring device of which, graduated in revolutions, is conveniently located near the steering.

Electronic tachometer for a car. Scheme of an electronic tachometer for a car

Fig. 1

The basis of the tachometer is a controlled multivibrator on transistors T1, T2. It gives narrow rectangular pulses, with a duration of about 0,5 microseconds, with a constant amplitude. The constancy of the amplitude of the output pulses is achieved by stabilizing the voltage supplying the multivibrator using the Zener diode D1.

The transistor TK, connected according to the emitter follower circuit, serves to match the output resistance of the multivibrator with the internal resistance of the measuring head of the IP. The indicator gives readings when pulses from the multivibrator arrive at the base of the transistor TK. Since their amplitude and duration are constant, the instrument readings are directly proportional to the repetition rate of these pulses. The more often they are, the greater the reading of the device.

The pulses controlling the multivibrator are fed to the capacitor C3 and the base of the transistor T2. They are obtained from a capacitive sensor made in the form of several turns (5-10) of PELSHO 0,31 wire wound on a common wire supplying power to the distributor (Fig. 2). To prevent the sensor from moving along the wire, its beginning and end are reinforced with sticky vinyl chloride insulating tape.

Fig. 2

The device is calibrated according to the scheme (Fig. 3) using a rectangular pulse generator. The voltage at the output of the generator is set to about two volts. When the tachometer is operating, it receives 4, 6 or 8 pulses (from the ignition system) per revolution of the engine shaft, depending on the number of its cylinders. Thus, the number of revolutions will be equal to the number of pulses received divided by the number of cylinders. For example, if the frequency of impulses from a 4-cylinder engine is 10 per minute, then its number of revolutions is 000: 10 \u000d 4 rpm.

Electronic tachometer for a car. Calibration scheme for an electronic tachometer for a car

Fig. 3

The readings of the device may be unstable or incorrect if pulses with an excessively large amplitude are supplied from the speed sensor. In this case, it is necessary to reduce the number of turns of the sensor.

If it is not possible to use a measuring signal generator, then with sufficient accuracy for practice, you can calibrate the tachometer using a conventional ohmmeter. In this case, you need to select the total resistance of the resistors R7 and R8 according to the table.

Max RPM	4-cylinder	6-cylinder
rev / min	R7+R8, Ohm	R7+R8, Ohm
5 000 8 000 10 000	180 520 800	500 1200 1500

The design of the device can be any. The easiest way is to attach the circuit board, which carries the main elements, to the back of the pointer device, to its output terminals.

In the tachometer, you can use any low-frequency, low-power transistors, for example, MP40 and a Zener diode D808 or D809.

Literature

Practical Wireless #2 1972

Publication: cxem.net

See other articles Section Automobile. Electronic devices

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Artificial leather for touch emulation 15.04.2024

In a modern technology world where distance is becoming increasingly commonplace, maintaining connection and a sense of closeness is important. Recent developments in artificial skin by German scientists from Saarland University represent a new era in virtual interactions. German researchers from Saarland University have developed ultra-thin films that can transmit the sensation of touch over a distance. This cutting-edge technology provides new opportunities for virtual communication, especially for those who find themselves far from their loved ones. The ultra-thin films developed by the researchers, just 50 micrometers thick, can be integrated into textiles and worn like a second skin. These films act as sensors that recognize tactile signals from mom or dad, and as actuators that transmit these movements to the baby. Parents' touch to the fabric activates sensors that react to pressure and deform the ultra-thin film. This ... >>

Petgugu Global cat litter 15.04.2024

Taking care of pets can often be a challenge, especially when it comes to keeping your home clean. A new interesting solution from the Petgugu Global startup has been presented, which will make life easier for cat owners and help them keep their home perfectly clean and tidy. Startup Petgugu Global has unveiled a unique cat toilet that can automatically flush feces, keeping your home clean and fresh. This innovative device is equipped with various smart sensors that monitor your pet's toilet activity and activate to automatically clean after use. The device connects to the sewer system and ensures efficient waste removal without the need for intervention from the owner. Additionally, the toilet has a large flushable storage capacity, making it ideal for multi-cat households. The Petgugu cat litter bowl is designed for use with water-soluble litters and offers a range of additional ... >>

The attractiveness of caring men 14.04.2024

The stereotype that women prefer "bad boys" has long been widespread. However, recent research conducted by British scientists from Monash University offers a new perspective on this issue. They looked at how women responded to men's emotional responsibility and willingness to help others. The study's findings could change our understanding of what makes men attractive to women. A study conducted by scientists from Monash University leads to new findings about men's attractiveness to women. In the experiment, women were shown photographs of men with brief stories about their behavior in various situations, including their reaction to an encounter with a homeless person. Some of the men ignored the homeless man, while others helped him, such as buying him food. A study found that men who showed empathy and kindness were more attractive to women compared to men who showed empathy and kindness. ... >>

Random news from the Archive

MPC17C724 - motor driver chip 27.01.2006

The FREESCALE SEMICONDUCTOR MPC17C724 motor driver IC is ideal for portable electronic applications such as bipolar stepper motors, DC motors for video cameras.

The chip is very small (3x3 mm), so it can be used in mobile phones with a built-in digital camera function.

News feed of science and technology, new electronics

We recommend downloading in our Free technical library:

▪ site section Electrician's tool

▪ Power Machines magazines (annual archives)

▪ book Broadcast television node. Kornienko A.Ya., 1950

▪ article by Thales of Miletus. Famous aphorisms

▪ article Worker of small enterprises and firms. Standard instruction on labor protection

▪ article Thermometer on the microcontroller. Encyclopedia of radio electronics and electrical engineering

▪ reference book Foreign microcircuits and transistors. Y-series

Leave your comment on this article:

All languages of this page

Home page | Library | Articles | Website map | Site Reviews