A tachometer is a device for converting a non-electric parameter (rotational speed) into an electrical one (pulses, voltage, amperage). With it, you can determine the number of turns 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 virtually any reading device. Very often used sensors:
The principle of operation of the tachometer on the microcontroller
If we take as a basis the modern element base, then it is possible with the use of several microcircuits to build a completely working homemade tester on LEDs or using an LCD display. Moreover, the options of readers can be a great many. It is possible to envisage both an inductive connection and a Hall sensor. The process of transformation in the tachometer on microcontrollers:
The device tachometer.
- On the axis of rotation is a disk, on the edge of which there is a protrusion - one tooth of small height. Disk size can be absolutely anything. The main thing is that the response speed of the sensor allows you to fix one turn.
- A sensor is installed opposite the disc tooth. It works only during the passage of the tooth near it.
- The tachometer reader receives a signal to the transducer if the signal level is small. The converter consists of an operational amplifier, which increases the signal level several times.
- The signal from the op amp enters the pulse counter. It can be performed on a simple microcontroller. Only it must be embedded software.
- The number of pulses counted by the controller is fed to a device that performs the calculation of data. This is the same microcontroller, but it has a different algorithm. The device according to a certain scheme, which is incorporated in it, considers the number of revolutions for a certain period of time.
- The next step is the conversion of a digital signal into a visual form. This task is handled by an LCD indicator with a microcircuit that controls it.
Simple device for measuring rotational speed
As a basis for the manufacture of a tachometer, you can take a calculator.
But you can build a tachometer not only with microcontrollers. In the absence of an element base, even a simple calculator 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 revolutions per minute. But the calculator will serve as a good pulse counter. As a signal device (sensor) it is allowed to use inductive sensors, as well as many others. When the disc is rotated, only one impulse per revolution should appear on the sensor. Moreover, the sensor contacts must be normally open, and at the time of passage of the tooth of the disk, they are closed.
This is ideal if you decide to use a home-made simple tachometer based on a calculator. But such a device would be useful if the measurement needs to be done very rarely. If constant monitoring of speed is required, it is better to use more reliable devices. Contacts are simply soldered parallel to the addition button of the microcalculator. When measuring the rotational speed, the following actions are performed:
- Turns on the calculator.
- The "+" and "1" buttons are pressed.
- A device is started, on which it is necessary to measure the rotational speed. At the same time, the stopwatch is activated.
- A countdown of 30 seconds is made, after which the value is recorded on the screen of the calculator.
- This is the number of revolutions in 0.5 minutes. Having doubled it, you get the value in 1 minute.
Analog and digital tachometers
A homemade tachometer can be of two types:
The differences are visible from the titles. The first convert the electronic signal and give it to the display device - voltmeters, ammeters, LEDs. The second converts the analog signal into a sequence of zeros and ones, which are easily recognized by microcontrollers. The latter work with such complex combinations, ultimately converting the initial value into numbers on the display.
Analog tachometer circuit.
Analog tachometers consist of the following main nodes:
- an electronic chip that acts as an amplifier and analogue signal converter;
- wiring connecting all elements of the tachometer;
- scales with a specific graduation, which is applied by simultaneously measuring the speed of rotation with a reference tachometer (instead of the scale, LEDs mounted one behind the other can be used);
- arrows indicating the current value of the desired value;
- electromagnetic coil on which the axis for the arrow is located;
- reader - breaker (in its quality often serves as an inductive sensor).
Digital tachometer circuit.
Digital tachometers perform a similar function, but consist of other nodes:
- ADC with 8 digits;
- a central processor that performs the function of converting an analog signal to a sequence of 1 and 0;
- LCD display to display the current value of a certain value;
- RPM sensor - breaker, must be used either with an amplifier or with shunts, depending on the design;
- a special chip that allows you to reset the current values to zero;
- in cars, liquid temperature sensors, in the cabin, oil pressure, speed, and many others can be connected to the CPU.
A tachometer using a microcontroller must necessarily have software.
In the "heart" of the chip with the help of a personal computer, a certain algorithm is laid by which the work is carried out. The processor calculates mathematical formulas that depend on which parameter is to be measured. When monitoring a single value, the algorithm will be the easiest.
But the digital tachometer in the car can also be used as a recorder of temperatures, pressure, speed. The microcontroller has several inputs and outputs. Readers are connected to them through buffer stages - converters and signal amplifiers. But It is worth noting that when introducing additional equipment into the tachometer design, it is necessary to take this into account in the algorithm and software of the microcontroller.
To make a homemade digital tachometer, you need knowledge of a personal computer and programming language. The ability to write algorithms will also prove useful. Therefore, it will be simpler to use conventional microcircuits, which will amplify the interrupter signal and give it to the strip of LEDs or a dial indicator. If there is a series of LEDs consisting of 10 pieces for every thousand revolutions, then the current value can be determined with an accuracy of one hundred.