Connecting a tachometer to an electronic ignition coil. Tachometer on a car, tachometer does not work, causes of tachometer breakdowns, do-it-yourself repairs

Every modern car is equipped with a device such as a tachometer. Information on how to connect a tachometer will be useful to owners of the first models of the VAZ family, as well as other cars that were not equipped with this important device from the factory.

Many motorists are well aware that the use of a tachometer makes it possible to increase the service life of the engine, since it is this device that helps determine the optimal moment for changing gear. Although beginners are more likely to look at the tachometer, its installation helps every motorist. The tachometer is not only used while driving, it is also used to adjust the carburetor and other devices while idling.

The connection of the tachometer can be carried out on any machine, regardless of which power unit is located in the engine compartment - diesel or gasoline. Consider the methods of connecting the tachometer in more detail.

Installing a tachometer on a car with a gasoline engine

If the vehicle is equipped with an ignition system, the device itself is installed first. Often, motorists use a remote tachometer. The tachometer connection diagram looks like this:

• wire "minus" (as a rule, it has black insulation) - to the mass of the machine;
• power wire (red) - the corresponding terminal of the ignition switch;
• the wire connected to the measuring input of the device - to the terminal of the ignition coil, which is connected to the distributor breaker (this option is relevant for cars with a contact circuit, but if a non-contact circuit is used, we connect the third wire of the tachometer to the voltage switch).

As a rule, tachometers are equipped with a backlight, which is recommended to be connected to the “dimensions” of the car (this must be done through a special ignition switch terminal).

Connecting a tachometer on a car with a diesel engine

Owners of cars equipped with a diesel engine should also know how to connect a tachometer. In such a situation, the measuring wire of the device is connected to the generator terminal, which is indicated by the symbol "W". If you could not find it, you need to disassemble the generator in order to get to the wires connecting the rectifier and the winding. We connect the tachometer wire to one of them. Be sure to insulate everything well.

Then the generator is reassembled. At the end of our article, I would also like to advise you to take into account the features of the devices during their selection. So, tachometers for diesel and gasoline engines use different methods for determining the number of incoming pulses, so before purchasing a specific device, do not forget to ask if the tachometer will work correctly on your car.

Get the tachometer and suitable terminals. You can buy and install both a new device (its price is in the range of the equivalent of $ 30-50), and an inexpensive used tachometer.

• The only extra you need is a set of quick connectors. You can buy them at any auto electric store for the equivalent of $2-$3. Keep in mind that the wire size is usually 0.5-1.0 mm², so choose the right size terminals.

The tachometer is a device that is actively used on gasoline and diesel vehicles. This device is used to measure the speed of rotation (revs) of the crankshaft or generator. Most modern vehicles are equipped with a standard tachometer directly from the factory.

The need to independently install a tachometer on a diesel engine may arise for various reasons. It should be noted that the connection scheme for a tachometer on a diesel engine is somewhat different from a similar solution for gasoline ICEs. In the process of choosing a tachometer for a diesel engine, this feature must be taken into account, since a tachometer for gasoline engines will not work on a diesel engine.

Read in this article

Where does the tachometer signal to the diesel engine

Today, for diesel engines, electronic, digital and analog tachometers are on sale, the connection diagram of which involves a number of features. The fact is that in the overwhelming majority of cases, the generator acts as the connection point for the tachometer for a diesel engine.

To implement the connection to the generator, you must have the tachometer itself, an insulated wire and the accompanying instructions for installing and operating an automobile tachometer.

Device connection

The principle of operation of an electronic tachometer is based on the reading of electrical impulses. In gasoline units, pulses are read, which are fed in a certain amount to the ignition coil. As for the diesel engine, the reading is carried out from a special terminal, which is located in the generator housing.

Read also

Why a diesel engine does not need to be twisted like a gasoline engine. Features and differences of diesel internal combustion engines in comparison with gasoline. Optimal turnover.

A tachometer is a device for measuring the rotational speed of engines, shafts, and other mechanisms. In transport technology, the tachometer has been used for more than a hundred years. As a rule, it is installed on the dashboard. The device indicates the rotational speed of the internal combustion engine during its operation. In modern cars equipped with electronic engine control systems, it is not always installed. However, the tachometer readings allow you to select the most suitable driving mode. In some cases, this allows you to save fuel or, conversely, switch to a more aggressive driving style. Therefore, experienced motorists, professional drivers often install dashboards with tachometers on their own.

Consider how to make an independent connection of the tachometer.

The principle of operation of the tachometer

Currently, tachometers are distinguished:

• Mechanical. Information about the engine speed is supplied to the mechanical tachometer using a rotating cable mechanically connected to the engine crankshaft. Now such devices are practically not used in cars;
• Electromechanical. The principle of operation of electromechanical tachometers is based on the conversion of electrical impulses from sensors installed on the engine or from other electronic devices. These signals are converted into magnetic impulses that deflect the pointer of the measuring device like a pointer voltmeter;
• Digital. Digital tachometers are used as part of modern computerized panels and are controlled by software and hardware. Self-installation of this type of tachometer is almost impossible.

Ways to turn on the tachometer

Information about the rotational speed of an internal combustion engine can be read from:

• generator;
• crankshaft speed sensor;
• camshaft speed sensor;
• ignition coil control pulse.

Alternators of some cars (for example, Volkswagen T4) have an additional AC voltage output, the frequency of which depends on the engine speed. In these machines, the signal to the tachometer is supplied from this point.

It is irrational to change the generator only to install a tachometer.

The crankshaft and camshaft speed sensors work on the electromagnetic principle. Earlier vehicles had sensors using the Hall effect. In any case, the electrical impulse generated by these devices has an amplitude of not more than 5V, their internal resistance is not less than 200 ohms. In order to connect the tachometer to these sensors, an additional amplifier is required. It is most efficient to use a more powerful impulse coming to the ignition coil.

Ignition system of petrol engines

Control of engine ignition processes can be organized in several ways:

• Distributor with one ignition coil;
• Tramblerless with a dual (triple, quadruple, depending on the number of cylinders divided by 2) ignition coil;
• Individual (for each spark plug).

In all cases, a powerful pulse with an amplitude of 12V is supplied to the coil from a chopper (for cars up to the 90s), a transistor switch, or directly from the engine control unit. It is from this point that the signal to the tachometer should be taken.

Technical solution

Before connecting a tachometer, it is necessary to draw up an electrical connection diagram in order to mentally determine the start and end points of switching on, and trace the conductor. Any ignition coil has an output (terminal) +15 (ignition on), which is supplied with battery voltage when the key is turned to the first (for some cars - the second) position. In no case should you connect a tachometer to this point, the first time you turn it on, it may fail. High-voltage wires are also dangerous, even for humans. The signal input to which the tachometer is to be connected must be precisely defined. In older coils, it is marked with the letter "K", it is better to find the exact electrical circuit diagram of the car.

The next, more difficult task is the electrical connection of the nodes. As a conductor, you should take a stranded copper wire with a cross section of at least 2 sq. Mm. with PVC insulation.

The connection points of the wire to the ignition coil are cleaned, mechanically twisted, soldered and carefully insulated. Lay the wire along any electrical harnesses, using plastic zip ties, towards the bulkhead of the engine compartment near the dashboard. You can enter the conductor inside the passenger compartment next to any wiring harness. To do this, it is easier to use an elastic string. Finally, connect the conductor to the signal output of the tachometer. In some cars that provide modifications with and without a tachometer, you can simply change the dashboard, find a regular conductor and connect it to the ignition coil.

Test, tachometer adjustment

If the car is equipped with a distributorless or individual ignition system, the tachometer can be connected to any coil. In this case, the readings of the engine speed (rpm) will be inadequate, since a pulse is supplied to the trampled ignition every cycle, an individual one - four times less often. However, it is possible to calibrate the measuring scale in a new way.

At the first stage of testing, the engine is started, the operability of the system is checked (deviation of the arrow at idle). As a rule, the speed in this mode is in the range of 800 - 1000 rpm.

Next, adjust the reading level. If the tachometer needle deviates slightly, you can connect an additional capacitor with a capacity of about 1 microfarad between the signal wire and the vehicle ground. On the contrary, if the arrow goes off scale, include a variable resistance of about 1 kOhm in the signal circuit break and scale the signal.

The next step is sea trials. On a running engine, they reach the maximum speed. The tachometer needle should not go into the red zone. Otherwise, the adjustment is carried out again. Before starting operation, once again check the reliability of connections and insulation. And remember, additional hardware brings new challenges.

Not really

Many motorists are well aware of why and for what purpose engineers came up with a tachometer in cars. Some do not look at it at all, and on some cars its presence is not provided. Is there an electronic tachometer for these cars?

What does it represent?

Before we talk about electronics, let's see what this device is for in general.

So, this is a special device that is installed on cars to control the crankshaft speed. So, this device shows the driver at what frequency the motor rotates. This is necessary so that the driver does not exceed the permissible speed.

main function

The tachometer helps inexperienced drivers who still cannot determine the speed by the sound of the unit, to choose the right gear. Riding in the right gear allows not only to significantly increase the resources of the power unit components, but also save fuel. When the arrow of the device enters the red zone, it is recommended to shift to a higher gear. Also, this device is used to adjust carburetors both at idle and while driving.

Operating principle

The tachometer registers the number of pulses that are supplied from the sensors. Pauses between impulses and the order in which they arrive are also taken into account. The counting process can be carried out using both forward and reverse directions. Indicators are often translated into a certain value. This value can be any indicator. Most of these devices can be reset. As for the accuracy of the readings, it is rather conditional. The best quality electronic tachometer has an accuracy of about 100 rpm.

Digital tachometer device

If we consider this device, then this device consists of:

• central processor;
• 8 or more bit ADC;
• coolant temperature sensor;
• display;
• optocoupler, which is used for diagnostics;
• reset block.

Electronic switch devices

The electronic tachometer is in most cases made in display format. The readings are displayed on this screen.

These are the revolutions of the crankshaft. Especially these devices are convenient in the arrow version. Switch equipment can most often be seen on dashboards. Drivers find it very convenient, as the signals from the sensors are transmitted to the arrow. Scientists have proven that the brain perceives information better from the arrow, in contrast to the numbers on the display.

We assemble an electronic tachometer with our own hands

Why buy when you can assemble everything yourself? It's not that expensive and quite interesting. For assembly, there are several options for devices. These devices are assembled on the basis of contact or non-contact sensors. In non-contact systems of the optical type, laser or infrared beams are used to register pulses. The time of one revolution is calculated. Let's see how to build your own optical registration device using an Arduino-type microcontroller.

Electronic tachometer circuit on Arduino

To assemble the device, you will, of course, need an Arduino microcontroller. If it is not there, then any other controller with similar characteristics will do, but then you will need to additionally assemble the programmer. Also, for this circuit, resistors of 33 kOhm, 270 Ohm, 10 kOhm are needed in the form of a potentiometer. You can also purchase a blue LED, an infrared LED and a photodiode. Next, find the DSW display and shift register chip labeled 74HC595. It uses an optical sensor and the principle of reflecting rays. With this system, you don't have to worry about how thick the rotor should be, and the number of rotor blades won't change the performance. The sensor will be able to accurately read the revolutions.

Assembling the sensor

First of all, to create a sensor, you need an infrared diode and our photodiode. In the first step, sand the diodes until they are flat. Then it is recommended to fold a strip of paper in the form of a rectangular tube.

Further on the scheme

Resistors and their ratings may vary slightly. It depends on the diodes. A variable resistor makes it possible to change the sensitivity level of the resulting sensor. So, the "ground" is connected to a 33 kΩ resistor and to a variable resistor, and that, in turn, is connected to a wire that needs to be installed in front of the potentiometer. The minus of the LED is connected through the remaining resistor to the ground, and the plus goes to the Arduino. So, it turned out three conclusions - ground, plus and a signal wire. This circuit uses an 8-bit shift register and display. In the case, it is desirable to think over the recesses for the indicator. Now a 270 ohm resistor is soldered to the LED and then installed in pin 12 of the microcontroller. Now the electronic tachometer is ready. You can do its programming and calibration. The program for "Arduino" can be found on automotive resources.

Another homemade tachometer

In order to measure the number of revolutions, as we already know, the pulse count of the interrupter is used or the voltage from the spark plugs. The frequency of these pulses is linearly related to the speed of the motor. You can also try to organize an inductive connection with such a circuit, which will be demonstrated in this device. The single vibrator marked LM 555 is used as the basis for this option.

The element is launched due to impulses from candles that are induced in the coil. The input contact is used either for setting or for signaling from the interrupter. For an ordinary four-cylinder unit, the speed of which is 3000 rpm, the frequency is 100 Hz. For 1500 rpm - 50 Hz. This makes it possible to easily calibrate the device in terms of frequency. The pulses received from the third output of the microcircuit are fed to the dial indicator. In this circuit, the author uses a milliammeter. The indicator will show the voltage in this network. Since the duration of the pulses at the output of the microcircuit is approximately the same, the voltage is proportional to the frequency with which sparks are formed. So, the scale of the measuring device can be redrawn by calibration. The head from an old cassette recorder is excellent as a coil. It should be located near the high voltage coil. To protect the microcircuit, you can use a 12 V diode.

Tachometer for motorcycles

How to put an electronic tachometer on a motorcycle? Here, the owners of motor vehicles have a choice: either purchase ready-made equipment, or make it yourself. Suppose that there is a motorcycle, there is a device for controlling speed. But how to connect an electronic tachometer? The device TX-193 from the six for these purposes is best suited for mounting on domestic brands of motorcycles.

The device has extraordinary accuracy, low weight, economical power consumption, as well as stable operation in vibration conditions. I must say that this model cannot even be compared with any tachometers for motorcycles. The process of connecting the device to two-cylinder motorcycles with a starter and a battery, as well as single-channel ignition, is no different from the process of connecting the same device to a VAZ. The input of the device is connected to the output of the primary winding of the ignition coil. The device can be powered by a battery. For this, the unit has the appropriate wires. It is then recommended to install a switch in the positive cable. This is useful when the technique is at a standstill. This way you can save battery power.

If the motorcycle is not domestic and there is still the same electronic tachometer, the connection diagram will change slightly. In this case, you will have to power through the ignition switch. There are special contacts for these purposes. If the motorcycle does not have a starter, then the battery should be connected to the rectifier output. And from the battery it is already possible to supply power directly to the tachometer through the switch. If there is no rectifier, you need to buy one. If there is no battery, you can put it. The easiest option is a power source from a UPS or an old flashlight. If you connect a measuring device directly to the generator coil, then it will burn out. To avoid this, you can ask a neighbor radio amateur to make a voltage regulator on thyristors.

If the engine has three cylinders, then signals from two coils are input here. There are also technical possibilities for installing a tachometer on six-cylinder motorcycles, but this already requires the purchase of branded equipment.

Installing a tachometer on VAZ cars

You can purchase a freelance electronic tachometer (VAZ 2109 is not equipped with these necessary devices on a regular basis) and enjoy life. Modern devices are also multifunctional. On many of them, the car enthusiast will additionally find an alarm clock and many other useful things.

It is worth noting that these devices differ in the type of engine power. For gasoline engines, the principle of operation is one, for diesel engines - completely different.

Gasoline devices also have differences in the number of cylinders

So everything is bought. Now decide where you will install the electronics. Many put it on the dashboard, others mount it near the ignition switch. However, it is best if the electronic tachometer is installed in a place where it will not spoil the appearance of the panel.

For fixing, the best friend of a motorist will help - double-sided tape. This universal tool saves in a variety of situations.

Do-it-yourself device connection

Not everyone understands electronics, but it is still desirable to be able to connect a measuring device. This will not cause difficulties, because there are only three wires. The first thing to do is take the wire from the tachometer to the engine compartment. The easiest way to do this is through the hole in the speedometer cable. Next you need a piece of wire. It should be about one meter long, thin and hard. At one end, secure the wire from the device with electrical tape. Try to work carefully. Gently insert the other end of the wire into the holes in the cable and push. Connecting an electronic tachometer can be done as follows. The positive wire is connected to the ignition coil (pin B). Connect the signal wire to contact K of the same coil. Minus connect to ground. Work as carefully as possible, the wires are very thin and very unreliable.

Now it remains to start the car and test everything. That's all. Now you know how to connect an electronic tachometer, and you can even assemble the device yourself if you wish. It won't take you much time and effort.