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Build Arduino Tachometer Using A3144 Hall Effect Sensor

Build Arduino Tachometer Using A3144 Hall Effect Sensor

In this article, we will build a tachometer. A tachometer measures the number of rotations of a wheel, fan, engine, etc. 

We will use the A3144 hall effect sensor to build a couple of projects which will read the speed of the fan and blink an LED.  

You find tachometers measuring the rotation speed of hard disks, motors in automobiles, aviation, 3-D printers, computers, etc. 

You can also use tachometers to measure the distance covered on your bicycle. 

In this article, we cover the basics of the A3144 sensor. We will learn the pin description and the specifications of the sensor.

Later, we will build the complete project. 

You will find step-by-step connections, Arduino code, and all the necessary information to program the Arduino and test your project in the real world.

At the end of the section, you will find many frequently asked questions with answers.

Let’s get started!

Components Needed To Build A3144 hall Sensor Tachometer Project

Hardware Components

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Basics of The A3144 Hall Effect Sensor

In this section, we will understand the features, specifications, and electrical interfaces needed to use the A3144 sensor in our tachometer project. 

The A3144 is a very sensitive hall effect sensor that can work over a wide temperature range.

There are 4 basic devices: A3141, A3142, A3143, and A3144. The A3144 is a three-terminal device.

Basics of The A3144 Hall Effect Sensor
Pin NamePin DescriptionRemarks
SUPPLYPower supply pinPin 1 of the IC. You can connect to 5V pin of the Arduino UNO
GROUNDPower return pinPin 2 – Ground connections
OUTPUTOutput pinPin 3 – Connect to any digital input pin of the Arduino UNO

The A3144 sensor can operate from 4.5 V up to 24 V. The wide operating range makes the sensor compatible with many applications. 

Features Of The A3144 Hall Effect Sensor

A3144 has a built-in voltage regulator. Hence the device can accept a wide range of voltage.

The internal regulator will regulate the input voltage and provide stable voltage for the operation of the chip. 

The hall sensors also incorporate a reverse battery voltage protection diode.

Accidentally, if you connect the power supply reverse, you won’t damage the device.

The diode will protect the device by blocking the current flow in the reverse direction. 

Small size and solid state reliability mean you can use the sensor in portable applications with vibration or stress.

Since there are no moving elements, the part will work reliably in applications with physical stress. 

The A3144 sensor is an open collector sensor. It supports up to 25 mA sink current. 

Functional Block Diagram Of A3144 Sensor

Functional Block Diagram Of A3144 Sensor

You can notice the following blocks in the functional diagram above. 

  1. Reverse Voltage protection
  2. Schmitt trigger output which provides hysteresis and avoids noisy outputs
  3. Open collector feature

The A3144 chip consumes about 4.4 mA (typical) current for regular operation.

Operation Of The A3144 Hall Effect Sensor

Pin 3 is the output pin of the sensor. You should provide an external pull-up for this pin. The pin goes low when you bring a magnet close to the IC. 

To be precise, the output pin three goes low when the magnetic field sensed is higher than the preset operating point threshold (magnetic field strength). 

When the magnetic field reduces, the output pin will again go high.

Here is the primary circuit you will need to work with the A3144 hall effect sensor.

A3144 hall effect sensor

-> Read our guide about What You Can Build with Adruino.

Step-By-Step Instructions To Connect The A3144 Sensor With Arduino UNO

In this section, we will build a project using Arduino UNO and the A3144 sensor.

Let’s get started with the hardware connections!

We will be using the chip directly. My personal preference is to use the A3144 IC as is.

It helps me bring the hall sensor as close to the magnet as possible.

Also, the sensor module’s overall size is more than the sensor alone. 

The smaller sensor allows me to easily insert the sensor in tight spaces such as moving disks, fans, etc.

You may also find the sensor module with the option to connect easily to the Arduino module!

The A3144 Sensor With Arduino UNO

The sensor module will have an LED to indicate the power.

LED to indicate the power

How To Connect The A3144 Hall Effect Sensor To The Arduino UNO?

Below is the step-by-step guide to complete the minimal connections needed to connect the Arduino and the A1344 hall effect Sensor. 

Step 1: Start with the GND connections.

Start with the GND connections

You can connect any GND pins available on the Arduino UNO board.

The ground pin on the Hall sensor is the pin in the middle.

Always start with the ground connections.

Connecting the GND pins first helps avoid accidental damage to the boards. 

Step 2: Connect the Resistor

Connect the Resistor

Hall sensor A3144 is an open collector output sensor. It would help if you connected an external resistor as a pullup.

You can use any value between 1 kOhms and ten kOhms. When the magnetic field is not present, the output pin will float.

Connecting an external resistor keeps the line at a high level. 

Step 3: Complete the power connections

Complete the power connections

Connect the 5 V pin of the Arduino UNO to the Supply pin of the A3144 hall effect sensor.

Congratulations, you have completed all the necessary connections needed.

Step 4: Connect the output pin

Connect the output pin

Connect the output pin to any of the Arduino GPIO pins. I have used pin A0 for the connection. 

Step 5: Verify the complete connection

Verify the complete connection

In the next sections, we will continue programming the Arduino UNO board to verify our connections.

Let’s continue!

-> Read our article about How Easy Is It To Learn Arduino?

Arduino Code Example For The Arduino and A3144 Sensor Project

In this section, we will walk through the example Arduino code to verify the A3144 sensor module. 

Project 1: The complete Arduino code for the A3144 sensor – Calculate RPM of the Fan

// Analog pin A0 is the hall pin, On the Uno the value of the A0 variable is 14
int hall_pin = 14;
// set number of hall trips for RPM reading (higher improves accuracy)
float hall_thresh = 100.0;
void setup() {
  // initialize serial communication at 9600 bits per second:
  // make the hall pin an input:
  pinMode(hall_pin, INPUT);
// the loop routine runs over and over again forever:
void loop() {
  // preallocate values for tach
  float hall_count = 1.0;
  float start = micros();
  bool on_state = false;
  // counting number of times the hall sensor is tripped
  // but without double counting during the same trip
  while (true) {
    if (digitalRead(hall_pin) == 0) {
      if (on_state == false) {
        on_state = true;
        hall_count += 1.0;
    } else {
      on_state = false;
    if (hall_count >= hall_thresh) {
  // print information about Time and RPM
  float end_time = micros();
  float time_passed = ((end_time - start) / 1000000.0);
  Serial.print("Time Passed: ");
  float rpm_val = (hall_count / time_passed) * 60.0;
  Serial.println(" RPM");
  delay(1);        // delay in between reads for stability

You have to mention the Arduino input pin planned to use for the connections here.

In our case, it is pin A0.

int hall_pin = 14;

In this code, you count the number of times the output pin of the sensor toggles.

The output pin will go low when the magnet is near the output pin will go high when the magnet is far. 

You can connect the magnet to the equipment where you want to measure.

For example, in the image below, you are attaching the magnet to the fan so that the magnetic field can be detected every time the fan makes one rotation.

connect the magnet to the equipment
  1. Magnet pasted on the rotating part of the fan
  2. A3144 hall effect sensor

Later, you can convert the number of times the hall sensor output pin went low into RPM (Revolution Per Minute). 

Project 2: Arduino Code Example For The Arduino and A3144 Sensor Project – LED toggle when Magnetic field is detected

const int hallPin = 2 ;     // initializing a pin for the sensor output
const int ledPin =  13 ;     // initializing a pin for the led. Arduino has built in led attached to pin 13
// variables will change
int hallState = 0 ;          // initializing a variable for storing the status of the hall sensor.
void setup ( ) {
  pinMode ( ledPin, OUTPUT ) ;       // This will initialize the LED pin as an output pin :
  pinMode ( hallPin, INPUT ) ;                         // This will initialize the hall effect sensor pin as an input pin to the Arduino :
  Serial.begin( 9600 ) ;
  Serial.println ("HALL SESNOR WITH ARDUINO") ;
  Serial.println ("Testing the analog hall sensor module:");
void loop ( ) {
  hallState = digitalRead ( hallPin ) ;                          
 // reading from the sensor and storing the state of the hall effect sensor :
  if ( hallState == LOW ) {                                            
 // Checking whether the state of the module is high or low
    Serial.println ("The state of the analog hall module is high");
    digitalWrite ( ledPin, HIGH ) ;                                  
// turn on the LED if he state of the module is high
  else {
    digitalWrite ( ledPin, LOW ) ;                                       
// otherwise turn off the LED :
    Serial.println ("The state of the analog hall module is low ") ;

FAQs About The A3144 Hall Effect Sensor And Arduino Projects

I have included a list of the most frequently asked questions about projects built using Arduino and the A3144 hall effect sensor.

If you have more questions, please post them in the comments section.

I will be glad to answer them.

1. How do you measure the magnetic field strength?

To measure the magnetic field strength, you can use the ADC of the Arduino UNO.

Depending on the proximity of the magnetic field, the analog voltage read by the Arduino UNO varies.

You should first measure the sensor’s voltage output with a known magnetic field to have a reference.

You can always calculate the magnetic field during actual measurements.

2. What are bipolar hall effect sensors?

The hall effect sensor can respond to the magnet’s north and south poles.

SS460S is an example of a Hall effect sensor that can react to both the north and south poles.

3. What are latching hall effect sensors?

The latching hall effect sensors provide you with digital-level signals. The latching-type sensors help build tachometers.

They simplify the solution as you can directly connect the sensors to Arduino boards.

If the sensors are non-latching, you need a comparator or similar circuitry to convert the analog value up to the threshold value as logic 0 and any value higher than the threshold to a digital high (5 V / 3.3 V).

4. Is the Hall sensor analog or digital?

The hall sensor measures the magnetic flux density. The measured value varies by the distance between the magnetic field source and the sensor.

You can find analog hall sensor modules and sensors that provide digital value.

Analog sensors help detect the strength of the magnetic field.

For example, you can use the analog sensor to measure the current flowing through a conductor.

Another use case is to detect the distance between the object and the sensor.

Digital hall sensors find their use cases to detect the object’s presence or count the number of rotations.

Hence both analog and digital hall sensors modules have their applications.

5. What are the advantages of the Hall effect sensors?

Hall effect sensors are beneficial in several applications.

  • The voltage generated is proportional to the magnetic field
  • Hall effect sensors are generally immune to noise, light, or temperature.
  • Hall effect sensing has no mechanical moving parts. Hene, the product supports a higher lifetime.
  • The sensing elements are highly reliable, and the results are reproducible.

> Check out our guide to the Top 12 Best Arduino Online Courses


In this article, we covered the basics of the Hall sensor A3144 and how you can use it to make an Arduino tachometer.

I shared with you the wiring connections and verified the links using the Arduino code example.

Hall effect sensors are used universally. I have built projects using a hall sensor to detect touch.

I will be happy to help you if you have any questions or doubts regarding the project.

If you have any feedback to improve the article, please share it in the comments section.

Your valuable input helps me to improve the article quality and bring more helpful content in the future.

Please remember to share the article with your fellow Arduino enthusiasts.