home > Internet > DIY speed meter. DIY car tachometer

DIY speed meter. DIY car tachometer

Before making a tachometer with your own hands, you need to understand the features of this device. The device is used to measure the number of revolutions of the power unit while driving. This information is displayed on a display located on the dashboard or a special screen. Let's look at the principle of operation of the tachometer and how to make it yourself.

We use a microcontroller

To make a tachometer with your own hands based on a microcontroller, you will need the following parts:

Directly microboard, an Arduino circuit will do.
Set of resistors.
For LED version you will need an LED element.
Diodes (infrared and photo analog).
Monitor. For example, LCD display.
Shift register

In the method discussed below, an optical regulator is used rather than a slot regulator. This will avoid problems with the thickness of the rotor, the number of blades will not affect the readings, and it will also be possible to read information about the drum speed.

Stages of work

Below is step-by-step instruction how to make a tachometer with your own hands based on a microcontroller:

To begin with, fine-grit sandpaper is used to sand the light and photodiode until they are flat.
A similar element is made in the form of a strip, then both parts are connected with glue and painted black.
At a further stage, diodes are mounted and wires are soldered to them.
The critical resistor values may vary depending on the photodiode used. The sensitivity of the controller will allow you to adjust the potentiometer.
Having studied the circuit of a car LED tachometer, you can understand that it has an eight-digit shift register. In addition, the circuit includes a liquid crystal display. To fix the light bulb, a small hole is made in the housing.
At the final stage, you will need to solder a resistor (270 Ohms) to the diode, then mount it into the socket. The controller is inserted into a cubic tube, which provides additional strength to the device.

Making a simple tachometer with your own hands

To make this device, a microcalculator is used as the basis. This option is suitable for those who have problems with the element base. It is worth noting that such a device does not provide 100% accuracy, and the tachometer will not display the number of rotations per minute on the display. Nevertheless, the calculator is a good alternative to other signal counting devices.

To manufacture the signal regulator, inductive or similar controllers are used. When the disk rotates, the display shows one signal after each rotation. The contacts must be open at this moment. They close when the assembly passes the disc tooth. The tachometer in question (it’s quite easy to make it yourself, as we see) of this type is excellent for those cases where measurements are rarely taken. For those who want to install a regular speed controller, it is better to opt for more reliable devices.

Exploitation

The simplest tachometer, made with your own hands on the basis of a calculator, works after soldering the contacts to the addition button of the computer.

Measuring the rotation speed is performed as follows:

The micro calculator turns on.
The “+” and “1” keys are activated synchronously.
The gadget starts up and measurements are taken on it. To ensure accurate readings, the stopwatch should be turned on at the same time as the calculator.
Wait 30 seconds and then look at the screen. The corresponding value should appear on it.
This indicator is the number of revolutions in 30 seconds. Multiplying the number by two, we get the number of rotations per minute.

Analog option

An electronic tachometer, made with your own hands for a diesel or gasoline engine, is focused on converting an electronic pulse and transporting it to an indication device. Unlike this device, digital models convert the analog pulse into a certain sequence of zeros and ones, which is read and decrypted by the controller.

Analog tachometers include the following elements:

A microboard whose purpose is to convert analog pulses.
Wiring connecting all elements of the device.
A scale used to demonstrate indicators.
An arrow that affects the effective value.
A special reel with an axis ensures correct operation of the arrow.
Inductive controller type reading device.

How to make a digital tachometer with your own hands

Devices of this type have an identical purpose, but differ in structural elements. To build the device yourself, you will need the following parts:

The converter is eight-bit.
A processor that allows you to convert pulses into a chain of zeros and ones.
Display for showing readings.
Interrupting type device (rotation controller) with amplifier. Special shunts may be used for this purpose, depending on the specific situation.
Payment for resetting information.
Additionally, you can connect antifreeze, cabin air, engine fluid pressure, and the like to the processor.
To set up the normal operation of the device, you will need to install a special program.

Mechanical modification

A DIY mechanical car tachometer does not require power or control circuits. A permanent type magnet is rigidly fixed on the shaft. When it rotates, a vortex field is created, which carries with it a special container made of magnetic material. The rotation of the bowl is resisted by a spiral spring. The higher the rotation speed, the more actively the shaft equipped with an arrow deflects.

The main advantage of a mechanical device is its simplicity of design and the absence of the need to obtain electrical power. Among the disadvantages are the high error and the shifted lower measurement limit. It is worth noting that at low speeds the needle does not deviate.

Diagnostics

A do-it-yourself tachometer can also fail. To identify the cause of the problem, you will need to carry out diagnostics. In vehicles equipped with an OBD II interface, the check is performed using a scanner. In addition, the electronic device can be controlled using any The best option will become a known good device, oscilloscope or frequency meter.

The mechanical analogue is diagnosed using a drill or screwdriver. If you have a speed controller, it is easier to check. The tail part of the cable is fixed in the chuck, and the body of the device is rigidly fixed.

Repair

Repairing the device in question is not very difficult. The most difficult item to repair is the electrical circuit module. After localizing the fault, you will need to replace the defective element. As a rule, the wiring, indicator contacts, sensor, and magnet on the crankshaft most often fail.

With the mechanical version everything is much simpler. It is enough to replace the failed part with a new spare part. With such tachometers, cars have high mileage and are considered heavily used vehicles. Therefore, it will not be difficult to find the element on the automobile market or at a disassembly site. After repair, connecting the device does not require calibration.

Settings

A tachometer on a car, made by yourself, may require adjustment. Since in machines the indicator usually produces a couple of pulses per revolution of the motor shaft, when calibrating the device, the generator frequency should be set twice as high.

To ensure that setting the tachometer does not cause difficulties, it is necessary to study the principle of operation of the bridge circuit. For example, if the ratios of resistor values are equal, the voltages at the points are equal, which means that no current flows and the arrow is at zero. If you reduce the value of the first resistor, the voltage at one point will increase, but at the second it will remain unchanged. The current will flow through the milliammeter and the needle will begin to move. This means that when constant voltage at the second point and changes in this indicator at the first point, the tachometer needle will move relative to the scale.

Finally

Making a car tachometer with your own hands is quite possible if you have basic knowledge of electrical engineering and desire. All you need is a ready-made circuit, a soldering iron and the main parts. The work will take no more than two days, including dismantling and installation. You can choose a product according to your needs: from a simple device based on a calculator or a more advanced tachometer based on the ARDUINO circuit. Before starting work, study the principle of operation of the standard device on your car.

The tachometer is a device that is actively used on gasoline and diesel cars. This device serves to measure the rotation speed (rpm) of the crankshaft or generator. Most modern vehicles are equipped with a standard tachometer straight 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 tachometer connection diagram on a diesel engine is somewhat different from a similar solution for gasoline internal combustion engines. When choosing a tachometer for a diesel engine, you need to consider this feature, since the tachometer for gasoline engines will not fit on a diesel engine.

Read in this article

Where does the tachometer signal come from for a diesel engine?

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

To connect to the generator, you must have the tachometer itself, an insulated wire and accompanying instructions for installing and operating a car tachometer.

Connecting the device

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

Electrical circuit diagram

The presented tachometer circuit is distinguished by its simplicity and accessibility of parts for repetition due to the use of an integrated timer - the KR1006VI1 microcircuit (analogous to NE555).

The diagram consists of the following functional units. A pulse shaper made on VT1-VT2, a pulse width modulator on a DA1 chip of type KR1006VI1 and a resistor bridge on resistors R8-R13. An electrodynamic pointer microammeter is used to take readings. The disadvantages of the tachometer circuit include the need to balance the bridge for each type of milliammeter when repeating the circuit. But this is not a difficult operation.

The supply voltage to the tachometer circuit is supplied directly from the terminals of the car battery.

Principle of operation

When pulses arrive from a breaker or inductor used in a strobe, capacitor C1 is recharged through diode VD1 and resistor R1-R2, creating pulses based on transistor VT1, opening it. As a result, short positive pulses are formed on the collector of the transistor, switched on in switch mode, the duration of which is determined by the capacitance of capacitor C1. VT2 serves to invert pulses before applying them to input DA1. The pulse shape is shown in electrical diagram tachometer on the right side, upper oscillogram. The photo below shows the block diagram of KR1006VI1.

The integrated timer KR1006VI1 is connected according to a standard pulse shaper circuit. Based on the positive edge of the pulses arriving at input 2, the microcircuit generates positive pulses at output 3 with a width that varies linearly depending on the frequency of those arriving at the input. The frequency is higher, the pulses are wider. The initial pulse width depends on the time constant of R6, R7 and C3.

The pulses coming from pin 3 of the DA1 microcircuit are sent to the left arm of the tachometer bridge, which is formed by resistors R8-R9 and R11. The right arm of the tachometer bridge, which is formed by resistors R10 and R12, R13, receives a constant reference voltage of +9V from the integrated voltage stabilizer K142EN8A. Capacitor C4 prevents the tachometer needle from jerking when measuring low engine speeds. The stabilizer also provides power to all active elements tachometer. A microammeter is included in the diagonal of the bridge.

Thanks to this circuit solution, it was possible to eliminate nonlinear elements, obtain a linear reading of the milliammeter as the frequency changes and ensure high accuracy of engine speed measurements due to the extended scale. Since the tachometer, for reasons of overall dimensions, uses a small-sized milliammeter from the recording level indicator of a tape recorder, whose scale length is short, it was only thanks to the extended scale that it was possible to obtain high accuracy of readings.

The K142EN series stabilizer chips provide a stable output voltage over a wide temperature range, which is why the K142EN8A chip is used in the tachometer. Capacitors C2, C5 and C6 are installed to smooth out supply voltage ripples.

Construction and details

Since the circuit is simple, I did not develop a printed circuit board. All parts, except the milliammeter, were installed on a universal breadboard measuring 30 mm×50 mm. The photo shows how the elements of the circuit are placed.

A three-pin connector is used to supply the supply voltage and input signal. The milliammeter scale is printed on a printer and glued on top of its standard scale.

The board with the parts is secured in the cover of the strobe housing with screws. The milliammeter is installed in a rectangular window cut out in the housing cover and secured with silicone.

This design for placing the tachometer provides easy access to the strobe board; just remove the cover and disconnect the connector.

Tachometer setting

If no errors were made during the installation of parts and the circuit elements are in good working order, the tachometer will immediately begin to work. It will only be necessary to adjust the values of the bridge resistors. To do this, you need to apply rectangular pulses with a frequency taken from the table below from a pulse generator to the tachometer input and calibrate the scale.

Table for converting engine speed to frequency
Engine speed, rpm	700	800	900	1000	1100	1200	1500	2000	2500	3000	3500	4000	4500	5000	6000
Generator frequency, Hz	12	13	15	17	18	20	25	33	42	50	58	67	75	83	100
Generator frequency, 2×Hz	24	26	30	34	36	40	50	66	84	100	116	134	150	166	200

Since in cars the sensor usually produces two pulses per revolution of the engine shaft, when calibrating the tachometer you need to set the frequency on the generator to twice as high. For example, when calibrating a scale point of 800, it will be necessary to apply pulses with a frequency of not 13 Hz, but 26 Hz, to the tachometer input. A number of frequencies for this case are given in the bottom row of the table.

In order not to experience difficulties when calibrating tachometer scales, you need to know the principle of operation of the bridge circuit. In front of you circuit diagram bridge direct current. If the ratios of the values of resistors R1/R2 and R3/R4 are equal, the voltages at the diagonal points of the bridge A and B are equal, and the current does not flow through mA, the arrow is at zero.

If, for example, we decrease the value of resistor R1, then the voltage at point A will increase, but at point B it will remain the same. Current will flow through the milliammeter located diagonally on the bridge and the needle will deflect. That is, with a constant voltage at point B and a change in voltage at point A, the needle of the device will move relative to the scale.

In the tachometer circuit, the function of resistor R1 is performed by resistor R9, and so on. As the engine speed increases, the frequency and width of the pulses from the output of the microcircuit increases and thus the voltage at the left connection point of the milliammeter increases, the flowing current increases and the arrow deviates. The resistors in the bridge arms are selected in such a ratio that the bridge is initially unbalanced, and voltage equality at the milliammeter connection points occurs at 700 engine revolutions.

The resistor values in the diagram are indicated with a milliammeter frame resistance of 1.2 kOhm. If you use a device that has a different frame resistance, you will have to select the value of resistors R8, R9 and R12, R13, temporarily replacing them with variables. After calibrating the device, the resistance of the variable resistors is measured and they are replaced with constant ones.

Switch S1 can be omitted and the device can be configured to measure in the required range on one scale. In this case, the measurement accuracy will be reduced by half. With a stretched instrument scale, such accuracy will also be sufficient.

A tachometer made according to the proposed scheme is a complete device and can be used to measure the rotation speed of any shafts, for example, a motor boat engine, electric motors. Hall sensors, photo and electromagnetic sensors can be used as sensors. It is enough to modify the circuit of the input pulse shaper.

The main task of a tachometer in a car is to help select the correct gear, which has a positive effect on the life of the engine. Most cars already have an analog tachometer and when the needle approaches the red mark, you need to shift into a higher gear.

In addition, car owners use it for adjustment work, both at idle and to control the engine speed while driving.

The physical principle of operation of the tachometer is based on counting the number of pulses that are recorded by the sensors, the order of their arrival, as well as the pauses between these pulses.

In this case, counting the number of pulses can be performed using various methods: forward, reverse and in both directions. The results obtained are usually transformed into the quantities we need. This value can be considered hours, minutes, seconds, meters, and the like.

The design of all tachometers allows the obtained values to be reset. The accuracy of these measurement results is quite conditional, about 500 rpm; the most accurate electronic tachometers measure with an error of up to 100 rpm.

Car tachometers come in two types: digital and analog. A digital car tachometer consists of the following blocks:

CPU
ADC 8 bits or more
Liquid temperature sensor;
Electronic display
Optocoupler for idle air valve diagnostics
Processor reset block.

The display of a digital automobile tachometer displays the results of measurements of shaft and engine revolutions. A digital tachometer is very useful when adjusting operations with electronic ignition units of a car engine, when accurately setting economizer thresholds, etc.

Analog car tachometers are more common and understandable more car enthusiasts. It shows the measurement results using a moving arrow.

Usually analog tachometer consists of:

chip
magnetic coil
wires for reading information from the crankshaft
graduated scale
arrow

This tachometer works as follows. The signal from the crankshaft is transmitted through wires to a microcircuit, which determines the position of the arrow on a graduated dial.

It is best to have both types of tachometer in your car. So the digital one does an excellent job of adjusting the idle speed, checking the operation of the EPHH control unit (forced idle economizer) and checking the standard tachometer (since the digital tachometer has much higher accuracy). When driving a car, it is much more convenient to use a standard analog tachometer, because the human eye and brain analyzes analog information better and faster than its digital value, and better accuracy while driving vehicle not required at all.

In addition, tachometers are also classified according to the installation method. There are standard and remote car tachometers. The first one is mounted directly into dashboard car. “It” is simpler and is used in most cars. The remote tachometer is designed for installation on the dashboard. They are used to give the car a more tuning appearance. appearance. The design of the remote tachometer has a leg for securing it to the dashboard.

Below is a diagram of a quasi-analog electronic tachometer. The principle of its operation is as follows. Engine speed is displayed on a simplified linear LED scale. The digital tachometer scale consists of nine LEDs. Each of these roughly corresponds to 600 rpm of the engine. At idle, only the first LED lights up. The tachometer is adjusted by selecting resistance R6. Depending on it, you can set the indicators to the required number of cylinders. You can also change the division price.

The source of pulses for the correct operation of the digital tachometer can be a Hall sensor, which is present in the electronic ignition system, a shaft position sensor, and others. The main thing is that the sensor sends pulses to our circuit that change the resistance of resistor R1.

This circuit works as a simple frequency meter. Pulses that constantly come from the engine sensor are sent to the counting input of the K561IE8 decimal counter, and then to the LEDs. The circuit can be powered from a cigarette lighter or.

Diode VD1 KD522 protects the circuit from incorrect connection of power polarity. The crankshaft speed sensor sends pulses to the base of transistor VT1. We select resistance R1 depending on the sensor (in the diagram, the resistance is selected for the Hall sensor in the contactless ignition system of a carburetor engine). From the output of VT1, the pulses go to the Schmitt trigger, made on elements D1.1-D1.2. It converts the pulses into the required rectangular shape. Capacitor C2 filters interference; paired with resistor R4, it forms a filter that cuts off high-frequency pulses. From Output D1.2, pulses are sent to the counter.

A multivibrator assembled on microcircuit elements D1.3 and D1.4 generates clock pulses with a frequency depending on R6. These pulses go to the C3-R7 chain, which forms a pulse to reset counter D2. Ultra-bright LEDs HL1-HL9 are connected directly to the outputs of the K561IE8 counter. Using R9 you can adjust the brightness of the display.

LEDs 1-4 on printed circuit board connected with an installation wire.

Setting up the design begins with calculating the value of resistor R1 in accordance with the range of incoming pulses. Then we replace R6 with series-connected variable resistors of 1 Ohm and constant resistors of 10 kOhm. Next, we tighten the variable resistor to maximum resistance. Then we turn it so that only two LEDs light up when the engine is idling. We mark this position of the tuning resistor. Then we reduce the resistance so that only one LED lights up. Then we adjust the resistor to the middle position. Next, we measure the resulting resistance R8 with a multimeter.

Most modern cars are equipped tachometers, facilitating the correct choice of gear, which extends engine life. If your car does not have such a device, then it can be made according to the proposed description.

Tachometer circuit shown in Fig. 1. Its main feature is the use of the K1003PP1 microcircuit, designed to control a linear scale of 12 LEDs. In the standard version, described in, the microcircuit provides the formation of a column of luminous LEDs, the length of which is proportional to the input voltage.

A signal, the frequency of which is proportional to the engine crankshaft rotation speed, is removed from the contacts of the breaker or from the shaper amplifier of the Hall sensor and is fed through the voltage divider R1R2 to the input of the Schmitt trigger DD1.1. The purpose of the trigger and capacitor SZ is to suppress bounce pulses at the breaker output, high-voltage surges on the ignition coil winding and bring the signal to standard CMOS logic levels with normal edge slope.

To enlarge, click on the diagram
Rice. 1 Tachometer diagram

The output of the Schmitt trigger triggers the standby multivibrator on IC DD2. In the main position of switch SA1 “6000”, the duration of the pulses generated by the standby multivibrator is 2.5 ms. At a rotation speed of 6000 rpm, the pulse frequency for a four-cylinder engine is 200 Hz, the repetition period is 5 ms, the duty cycle is 2. The integrating chain R12C6 averages these pulses, and the average voltage on capacitor C6 is about 3 V. This voltage is supplied to the pin . 17 (UBX) DD2 chips. With a voltage of 3 V applied to the pin. 3 (UB) of this microcircuit and determining the scale of the display, all 12 LEDs HL1...HL12 are turned on, forming a luminous column.

At lower engine speeds, the duty cycle of the pulses at output DD1 increases, the average voltage on capacitor C6 decreases in proportion to the speed, and the height of the column becomes smaller. When the engine is stopped, none of the LEDs light up. “Division price” of the LED scale is 500 rpm.

It is advisable to install LEDs different color glow. For example, if optimal performance engine corresponds to 2000...4000 rpm, LEDs HL1...HL3 can be used yellow or orange (“go to more low gear"), HL4…HL8 – green (“normal”), HL9…HL12 – red (“move to a higher gear”).

To adjust the idle speed, the switch should be set to position “1200”. In this case, the duration of the generated pulses will increase by 5 times and will be 12.5 ms, and the “scale division price” will be 100 rpm.

The tachometer microcircuits DD1 and DD2 are powered through the integrated voltage regulator DA1. Capacitors C1 and C2 ensure the stability of the stabilizer.

The current through the LEDs connected to the DA2 chip is determined by the voltage at its pin. 2. In the daytime, when the instrument panel backlights are turned off, a logic signal is present at the inputs of element DD1.2. 0, output – voltage 6 V, pin. 2 DA2 – about 0.85 V, which sets a current of 25 mA through each LED. In the evening, when you turn on the backlight, the voltage on the pin. 2 is reduced to 0.4 V, which reduces the current through the LEDs to 8 mA and, accordingly, their brightness.

A drawing of the tachometer printed circuit board is shown in Fig. 2. The design uses fixed MLT resistors and SPZ-19a tuning resistors. Capacitor C5 type K73-17 for a voltage of 250 V, C6 - K50-16, the rest - KM-5 and KM-6. DA1 chip - any 6 V voltage stabilizer, for example, KR1157EN6 with any letter index, KR142EN5B(G), KR1180EN6, 78L06, 7806 . The K561TL1 chip can be replaced with KR1561TL1, CD4093, CD4093B, and K1003PP1 with UAA180 or A277.

Orange LEDs - AL307MM (yellow ones usually glow weaker than others), green ones with increased brightness - AL307NM6, red ones - AL307BM. The LED leads are bent at an angle of 90°, and their axes are directed parallel to the printed circuit board. The size of the LEDs was reduced to 5 mm using a file.

Switch SA1 is any small-sized toggle switch; it should be installed in close proximity to the printed circuit board.

The unused inputs of the DD1 and DD2 microcircuits are connected either to the common wire or to the +6 V circuit.

Setting up the tachometer is quite simple. First, switch SA1 is set to position “6000”; pulses of positive polarity with an amplitude of 12 V with a frequency of 200 Hz and a duty cycle close to 2 are applied to the tachometer input to simulate connection to the breaker. The trimmer resistor R9 is used to make the entire LED column glow. If necessary, select the resistance of resistor R8. Then the same operation is performed for position SA1 “1200” at an input pulse frequency of 40 Hz.

LEDs can be arranged along a circular arc. In this case, the glow of one LED from the chain may be more effective. To ensure this mode of turning on the LEDs, their anodes should be disconnected from the outputs of the DA2 microcircuit and connected to the power pin (pin 18).

20.11.2020

Internet

The most interesting:

Label each polygon and measure the lengths of the sides of each

Connecting YouTube to TV

Names of large numbers Solving a compound problem