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. electronic tachometer best quality 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 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 appearance panels.
Helps to fix best friend car enthusiast - double-sided tape. This universal remedy 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.
Most modern cars are equipped tachometers facilitating right choice transmission, which extends the life of the engine. 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 chip, 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.
The signal, the frequency of which is proportional to the speed of the engine crankshaft, is taken from the contacts of the chopper or from the amplifier-shaper of the Hall sensor and through the voltage divider R1R2 is fed to the input of the Schmitt trigger DD1.1. The purpose of the trigger and capacitor C3 is to suppress bounce pulses at the output of the chopper, high-voltage surges on the ignition coil winding and bring the signal to standard CMOS logic levels with normal edge steepness.
click on diagram to enlarge
Rice. 1 Tachometer circuit
The output signal of the Schmitt trigger starts the waiting multivibrator on the DD2 chip. In the main position of the switch SA1 "6000", the duration of the pulses generated by the waiting 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 R12C6 integrating circuit averages these pulses, and the average voltage across capacitor C6 is about 3 V. This voltage is supplied to the pin . 17 (UBX) DD2 chips. At a voltage of 3 V applied to the pin. 3 (UB) of this microcircuit and determining the indication scale, all 12 LEDs HL1 ... HL12 are turned on, forming a luminous column.
At lower engine speeds, the duty cycle of the pulses at the output of DD1 increases, the average voltage across the 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 are lit. The “division price” of the LED scale is 500 rpm.
It is advisable to install LEDs of a different glow color. For example, if optimal performance engines correspond to 2000.. .4000 rpm, LEDs HL1…HL3 can be used yellow or orange (“switch to a lower gear”), HL4…HL8 green (“normal”), HL9…HL12 red (“switch to higher gear).
To adjust the idle speed, the switch should be set to the "1200" position. In this case, the duration of the generated pulses will increase by 5 times and will be 12.5 ms, and the "division" of the scale will be 100 rpm.
Microcircuits DD1 and DD2 of the tachometer are fed through an 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 lights are off, there is a log at the inputs of the DD1.2 element. 0, output - voltage 6 V, pin. 2 DA2 - about 0.85 V, which sets the current to 25 mA through each LED. In the evening, when the backlight is turned on, the voltage at 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 printed circuit board of the tachometer is shown in fig. 2. The design used constant resistors MLT, tuning SPZ-19a. Capacitor C5 type K73-17 for a voltage of 250 V, C6 - K50-16, the rest - KM-5 and KM-6. Chip DA1 - any voltage regulator for 6 V, 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 glow 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 in parallel printed circuit board. The size of the LEDs is reduced to 5 mm with a file.
Switch SA1 - 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 a common wire or to a +6 V circuit.
Setting up the tachometer is quite simple. First, the SA1 switch is set to the “6000” position, positive polarity pulses 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 a connection to a breaker. The entire LED column is lit with a trimming resistor R9. If necessary, select the resistance of the resistor R8. Then the same operation is performed for the position SA1 "1200" at an input pulse frequency of 40 Hz.
The LEDs can be arranged in a circular arc. In this case, the glow of one LED from the chain may turn out to be more effective. To ensure this mode of turning on the LEDs, their anodes should be disconnected from the outputs of the DA2 chip and connected to the power output (pin 18).
The electronic tachometer is digital device, made of electronic components and used to measure the speed of an electric motor or any other rotating object in revolutions per minute. It is located in the dashboard of the car good review and measurement accuracy.
Simple speed metronome
The tachometer comes from two Greek words: "tacho" means "speed" and "metronome" means "measure". It works on the principle of a generator and determines the voltage corresponding to the speed of the shaft. It is also known as a rev counter. Principle of operation:
- induction;
- electromagnetic;
- electronic;
- optic.
Historically, the first mechanical tachometer was developed from the measurement of centrifugal force. In 1817 they were used to measure the speed of traction machines, but after 1840 they were mainly used to measure the speed of vehicles. Digital tachometer - an optical sensor designed to determine the angular velocity of a rotating element. Areas of use:
Types of modern tachometers
An important parameter that is taken into account when choosing a device is the operating speed range. It sets the measurement limit that the device is able to control. Another parameter is precision, which is given in units such as ±RPM. Sensor technology used: contact, photoelectric, inductive and Hall effect.
In a contact type device, it comes into contact with a rotating part. A photovoltaic device uses light rays, either visible or infrared, to measure speed. The frequency of the break that is used to calculate the speed. Inductive tools use magnetic elements to induce magnetic fields and the activation frequency to measure speed. Design features:
- counters;
- timers;
- stroboscope.
Display configurations include analog visual indicators, digital or graphical video displays. User Interfaces and control types have analog faceplates or digital panels and computer programmable interfaces. Modern tachometers are equipped with software for running on a PC. Many have network or communication interfaces. Available electrical outlets:
- analog voltage;
- analog current;
- analog modulated frequency;
- switch or alarm;
- LED screen.
Tachometers are classified based on the data acquisition technology. Applied device types:
Microelectric Machine Generated Voltage
The tachometer generator converts the shaft rotation into an electrical signal. Its work uses the properties of the angular velocity of the rotor, the excitation flux, which is proportional to the generated EMF. Most modern tachogenerators are a permanent magnet type. These devices use a rotating joint, one end of which is connected to the machine shaft, to induce an electromotive force (voltage) proportional to the speed of the shaft. The armature contacts are connected to a voltmeter circuit, converting the voltage into a speed value.
These tachometers are distinguished by accuracy, maximum allowable performance and operating temperature. They are used as sensors in various automotive and electromechanical computer devices. They operate in AC or DC networks.
The principle of operation of the car meter
The tachometer is used to check the performance of the engine and helps the mechanic to understand the condition of the engine in order to optimize its performance within acceptable parameters. The principle of operation of an automotive electronic tachometer is simple. The ignition system triggers a voltage pulse from the electromechanical part of the tachometer, which responds to the average voltage of the pulses in proportion to the engine speed. The signal is transmitted by a double shielded cable to the indicator. The tachometers are temperature compensated to handle measurements in the -20 to +70 C ambient range.
It allows the driver to select the appropriate throttle and gear settings while driving, as long-term use at high speeds causes insufficient lubrication affecting the engine, creating overheating and causing unnecessary wear to friction parts and machine failure.
Engine speed check
During the operation of the car, you need to know how to check the tachometer at home. Most cars are equipped with a speedometer, pressure gauge, coolant temperature gauge and tachometer. They are installed differently depending on the make and model of the car. Sequencing:
With the wide possibilities of the electronics market, it is not difficult to make a tachometer circuit at home using a multimeter. Moreover, the results obtained in such circuits are accurate in assessing the overall operating condition of the system being measured.
Circuit diagram using IC 555:
The above setting is done with a conventional tachometer. Parts for manufacturing are widely available and can be purchased at any radio supply store. Parts list for homemade version:
- R1 = 4K7.
- R2 = 47E.
- R3 = 100 KB, may be variable.
- R4 = 3K3.
- R5 = 10K.
- R6 = 470 K.
- R7 = 1K.
- R8 = 10K.
- R9 = 100K.
- C1 = 47n.
- C2 = 100n.
- C3 = 100n.
- C4 = 33uF / 25V.
- T1=BC547.
- IC1 = 555.
- M1 = FSD meter 10 V.
- D2 = 1N4148.
- C5 with any value between 3.3uF and 4.7uF.
Before you make a tachometer with your own hands, you need to complete the installation documentation. simple circuit, designed using easily accessible elements with a rubberized MOC7811 opto-isolating module and two seven-segment displays, measures drive speed in RPS. This scheme calculates RPS from 00 to 99 if needed big values, add another decade counter.
The circuit diagram contains IC555, MOC 7811, IC CD4081, IC CD4069 and IC 4033 and the seven segment display unit LTS 543. On the first timer IC 555, configured as a monostable multivibrator, it generates a clock pulse when switch S2 is pressed, green LED 1 indicates the detection time .
The MOC 7811 IC2 contains an IR transmitter and a photodiode to create changing logical levels, depends on the blocking or interrupting IR beam. Logic gate N1 turns on the counter of the Johnson detector (CD 4033), it controls the LTS 543 seven-segment display. There are two decimal counters and two seven-segment displays for displaying RPS from 00 to 99.
According to this scheme, you can make a tachometer for a chainsaw with your own hands with a rotating chopper. One interruption of the infrared beam will be taken as one count, and the total rotation count is RPS, multiply 60 by RPS to get Revolution Per Minute (RPM).
Online app for iPhone
The capabilities of modern smartphones allow you to display on the display the tachometer of any car or motorcycle engine in real time based on the sound emitted. The RPM range is 400 - 90,000 rpm. You can find the application in App Store. After installing it, the tachometer dial will appear in large numbers at the top of the display, updating the value every ¾ seconds. RPM is calculated from the peaks in the autocorrelation plot.
The program provides hint controls that define the RPM range. There is background noise correction to truly define the sound of the engine. The tooltip is determined by the value of the center and tolerance in percent. By scrolling left or right in the blue bars below the tooltip, adjust the center RPM value and tolerance. Instead of a fixed range, a tracking mode is used that works over the entire measurement range.
In this mode, the tooltip controls are replaced, allowing true tracking to begin. Below the control data is a plot of the autocorrelation function to check the reliability of the displayed RPM. There is a guide to setting the RPM range. The vertical yellow lines on the graph correspond to the periods of sound produced by the engine. If they match well with the peaks on the graph, the RPM value is accurate. Audio to tone video conversion to RPM depends on engine configuration.
You can choose from several built-in configurations, including 4-stroke and 2-stroke motors, and specify an overall ratio that can compensate for any gear ratio between motor and shaft. In addition to this view, there are two configuration settings pages. Each has its own context-sensitive help that provides more information on how to use the application. There is also detailed guide for operation.
Early models of tachometers depended on mechanical actuators such as a flywheel, camshaft, fan pulley, etc. They rotate a magnet, thereby inducing eddy currents on an aluminum disk (speedometer) in revolutions per minute. A modern type tachometer is an electronic, pulse-controlled tachometer capable of measuring both the smallest and megaloads.
A tachometer is a device for converting a non-electrical parameter (speed) into an electrical one (pulses, voltage, current). With it, you can determine the number of revolutions for a certain unit of time (most often the interval is 1 minute).
The tachometer is designed to convert a non-electric parameter into an electrical one.
A homemade tachometer can be based on almost any reading device. Very often used sensors:
- inductive;
- Hall;
- capacitive;
- resistive;
- photoresistive;
- terminal.
The principle of operation of the tachometer on the microcontroller
If we take the modern element base as a basis, then using several microcircuits it is possible to build a completely working home-made tachometer on LEDs or using an LCD display. Moreover, there can be a great variety of options for reading devices. It is possible to provide for both the connection of an inductive and a Hall sensor. The process of transformations in a tachometer on microcontrollers:
- On the axis of rotation there is a disk, on the edge of which there is a protrusion - one tooth of small height. The size of the disk can be absolutely anything. The main thing is that the response speed of the sensor allows you to fix one revolution.
- A sensor is installed opposite the disc tooth. It works only during the passage of the tooth near it.
- From the tachometer reader, a signal is sent to the converter if the signal level is low. The converter consists of an operational amplifier, which increases the signal level several times.
- The signal from the operational amplifier goes to the pulse counter. It can be performed on a simple microcontroller. Only it must contain software.
- The number of pulses counted by the controller is fed to a device that calculates the data. This is the same microcontroller, but it has a different algorithm. The device, according to a certain scheme, which is embedded in it, counts the number of revolutions for a certain period of time.
- The next step is transformation digital signal into a visual view. This task is handled by an LCD indicator with a microcircuit that controls it.
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A simple device for measuring rotational speed
As a basis for the manufacture of a tachometer, you can take a microcalculator.
But you can build a tachometer not only with microcontrollers. In the absence of an element base, even a simple microcalculator will help to get out of the situation. A homemade tachometer based on it will not have high accuracy, and it will not work to display the number of revolutions per minute. But the calculator will serve as a good pulse counter. As a signaling device (sensor) it is allowed to use inductive sensors, as well as many others. When the disk rotates, only one pulse per revolution should appear on the sensor. Moreover, the contacts of the sensor must be normally open, and at the moment the tooth of the disk passes, they close.
This is ideal if you decide to use a homemade simple calculator-based tachometer. But such a device will be useful if the measurement needs to be carried out very infrequently. If constant speed monitoring is required, then it is better to use more reliable devices. The contacts are simply soldered parallel to the calculator's add button. When measuring the rotation speed, the following actions are performed:
- The calculator turns on.
- The "+" and "1" buttons are pressed.
- The device is started, on which it is necessary to measure the rotation speed. At the same time, the stopwatch starts.
- A countdown of 30 seconds is made, after which the value is fixed on the screen of the calculator.
- This is the number of revolutions in 0.5 minutes. Doubling it, you get the value in 1 minute.
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Analog and digital tachometers
Homemade tachometer can be of two types:
- analog.
- Digital.
The differences are visible from the names. The former convert the electronic signal and output it to the display device - voltmeters, ammeters, LEDs. The latter convert the analog signal into a sequence of zeros and ones, which are easily recognized by microcontrollers. The latter work with such complex combinations, eventually converting the original value into numbers on the display.
Analog tachometers consist of the following main components:
- an electronic microcircuit that acts as an amplifier and analog signal converter;
- wiring connecting all elements of the tachometer;
- scales with a certain graduation, which is applied by simultaneously measuring the speed of rotation with a reference tachometer (instead of a scale, LEDs mounted one after another can be used);
- an arrow indicating the current value of the desired value;
- an electromagnetic coil on which the axis for the arrow is located;
- a reader - an interrupter (an inductive sensor often acts as it).
Digital tachometers perform a similar function, but consist of different components:
- ADC with 8 bits;
- a central processor that performs the function of converting an analog signal into a sequence of 1 and 0;
- LCD display for displaying the current value of a certain value;
- speed sensor - interrupter, must be used either with an amplifier or with shunts, depending on the design;
- a special microcircuit that allows you to reset the current values to zero;
- in cars, sensors for fluid temperature, in the cabin, oil pressure, speed, and many others can be connected to the CPU.
A tachometer using a microcontroller must have software.
In the "heart" of the microcircuit with the help of personal computer a certain algorithm is laid according to which the work takes place. The processor calculates mathematical formulas that depend on which parameter needs to be measured. When monitoring a single value, the algorithm will be the simplest.
But a digital tachometer in a car can also be used as a recorder of temperatures, pressure, speed. The microcontroller has several inputs and outputs. Readers are connected to them by means of buffer stages - converters and signal amplifiers. But it is worth noting that when introducing additional equipment into the design of the tachometer, it is necessary to take this into account in the algorithm and software microcontroller.
To make a homemade digital tachometer, you will need knowledge of a personal computer and a programming language. The ability to write algorithms will also be useful. Therefore, it will be easier to use conventional microcircuits that will amplify the interrupter signal and give it to a strip of LEDs or a dial indicator. If there is a row of LEDs, consisting of 10 pieces for every thousand revolutions, then you can determine the current value with an accuracy of one hundred.
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 the display located on the dashboard or a special screen. Consider the principle of operation of the tachometer and how to make it yourself.
We use a microcontroller
To make a do-it-yourself tachometer based on a microcontroller, you will need the following parts:
- The microboard itself, the Arduino circuit will do.
- Resistors kit.
- For the LED option, you will need an LED element.
- Diodes (infrared and photoanalog).
- Monitor. For example, an LCD display.
- shift register
In the method discussed below, not a slotted, but an optical regulator is used. 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 revolutions of the drum.
Stages of work
Below is step-by-step instruction how to make a do-it-yourself tachometer based on a microcontroller:
- To begin with, the light and photodiode are processed with fine-grained sandpaper until they take a flat shape.
- A similar element is made in the form of a strip, then both parts are connected with glue and painted in black.
- At the next stage, diodes are mounted, wires are soldered to them.
- 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 scheme of the automobile LED tachometer you can understand that it provides an eight-bit shift register. In addition, the circuit includes a liquid crystal display. To fix the light bulb in the housing, a small hole is made.
- At the final stage, you will need to solder a resistor (270 ohms) to the diode, then mount it in the socket. The controller is inserted into the cubic tube, which provides additional strength to the fixture.
We make a simple tachometer with our own hands
For the manufacture of this device, a microcalculator is taken 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 percent accuracy, and the tachometer will not broadcast the number of rotations per minute on the display. Nevertheless, the calculator is a good alternative to other signal counting devices.
For the manufacture of the signal regulator, inductive or similar controllers are used. As the disc rotates, the display shows one beep after each revolution. The contacts should be open at this point. They close when the node passes the disc tooth. The tachometer in question (with our own hands, as we can see, it is quite simple to make it) of this type is perfect 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.
The rotation speed is measured as follows:
- Turn on the calculator.
- The "+" and "1" keys are activated synchronously.
- The gadget is launched and it is measured. To ensure accurate readings, turn on the stopwatch at the same time as the calculator.
- Wait 30 seconds and then look at the screen. It should show the corresponding value.
- This indicator is the number of revolutions in 30 seconds. Multiplying the number by two, we get the number of rotations per minute.
Analog variant
Do-it-yourself electronic tachometer for a diesel or gasoline engine is focused on conversion electronic pulse and transporting it to the display device. Unlike this device, digital models convert an analog pulse into a certain sequence of zeros and ones, which is read and decoded by the controller.
The following items are included in the package of analog tachometers:
- Microboard, the purpose of which is the conversion of analog pulses.
- The wiring that connects all the elements of the fixture.
- A scale used to demonstrate indicators.
- Arrow that renders on the effective value.
- Special spool with axle providing correct work arrows.
- The reading device of type of the inductive controller.
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 your own device, 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 demonstrating readings.
- Interrupting type device (rotation controller) with an amplifier. Special shunts may be used for this purpose, depending on the specific situation.
- Information reset fee.
- 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 mechanical car tachometer, made by hand, does not require power and control circuits. A permanent type magnet is rigidly fixed on the shaft. When it rotates, a vortex field is created, which carries along a special container made of magnetic material. The rotation of the bowl is resisted by a spiral spring. The greater the rotation speed, the more actively the shaft equipped with an arrow deviates.
The main advantage of a mechanical device is the simplicity of design and the absence of the need for electrical power. Among the minuses, one can note a high error and a shifted lower limit of measurements. It is worth noting that at low speeds the arrow does not deviate.
Diagnostics
A self-made tachometer can also fail. Diagnostics will be required to identify the cause of the problem. In vehicles equipped with an OBD II interface, the check is performed using a scanner. In addition, an electronic device can be controlled using any. The best option would be a known-good device, an oscilloscope or a frequency meter.
A mechanical analogue is diagnosed with a drill or screwdriver. If there is a speed controller, it is easier to check. The tail part of the cable is fixed in the cartridge, and the body of the device is rigidly fixed.
Repair
It is not very difficult to repair the device in question. The most difficult instance to repair is the module electrical circuit. After localizing the malfunction, it will be necessary to replace the defective element. As a rule, wiring, indicator contacts, a sensor, a magnet on the crankshaft most often fail.
With the mechanical version, everything is much simpler. It is enough to replace the part that has failed with a new spare part. With such tachometers, cars have high mileage and are classified as heavily used vehicles. Therefore, it will not be difficult to find an element in the automotive market or in disassembly. After repair, connecting the device does not require calibration.
Setting
A do-it-yourself tachometer on a car may require adjustment. Since in machines, usually, for one revolution of the motor shaft, the indicator gives out a couple of pulses, when calibrating the device, the generator frequency should be set twice as high.
In order to set up the tachometer without causing difficulties, it is necessary to study the principle of operation of the bridge circuit. For example, if the ratios of the resistor values are equal, the voltages at the points are equal, which means that the current does not flow and the arrow is at zero. If you reduce the value of the first resistor, the voltage at one point will increase, and at the second it will remain unchanged. The current will go through the milliammeter and the needle will start moving. This means that with a constant voltage at the second point and a change 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 realistic if you have elementary knowledge in electrical engineering and a desire. All you need is a ready-made circuit, a soldering iron and basic 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 calculator-based instrument to a more advanced tachometer based on arduino schematics. Before starting work, study the principle of operation of the standard device on your car.
