# DIGITAL TACHOMETER

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This is a Digital Tachometer using Hall Effect Magnetic Sensor, Arduino Nano and show the result on 4 Digit 7 Segment Display.

Its very simple project to build.

As you see on circuit diagram, we only need 4 resistors to limit the current for the 7 segment display.

COMPONENTS:

1. ARDUINO NANO V3
2. HALL EFFECT SENSOR MODULE
3. 4 DIGIT 7 SEGMENT DISPLAY (12 PINS)
4. 4 X 330OHM RESISTOR 1/4W 5%

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## Step 1: CREATE PCB & CODE

I'm using Fritzing Apps to create a PCB.

The size is about 40mm x 40mm using Single Layer PCB

There are four jumper on PCB.

THE CODE:

```// DIGITAL TACHOMETER// 4 DIGIT 7 SEGMENT DISPLAY
// by SAFT7ROBOTICS.comint sensorvalue;
int state1 = HIGH;
int state2;
float rps;
float rpm;
long prevMillis = 0;
long interval = 200;
long currentTime;
long prevTime = 1;
long diffTime;
int sensorthreshold = 30;//ABCDEFG,dp
const int numeral[10] = {
B11111100, //0
B01100000, //1
B11011010, //2
B11110010, //3
B01100110, //4
B10110110, //5
B00111110, //6
B11100000, //7
B11111110, //8
B11100110, //9
};//pins for decimal point and each segment
//dp, G, F, E, D, C, B, A
const int segmentPins[] = { 4, 7, 8, 6, 5, 3, 2, 9};
const int numberofDigits = 4;
const int digitPins[numberofDigits] = { 10, 11, 12, 13}; //digits 1, 2, 3, 4void setup()
{
//set segment and DP pins to output
for (int i = 0; i < 8; i++)
pinMode(segmentPins[i], OUTPUT);  //sets the digit pins as outputs
for (int i = 0; i < numberofDigits; i++)
pinMode(digitPins[i], OUTPUT);
}void loop()
{
if (sensorvalue < sensorthreshold)
state1 = HIGH;
else
state1 = LOW;
if (state2 != state1) {
if (state2 > state1) {
currentTime = micros();   // Get the arduino time in microseconds
diffTime = currentTime - prevTime;
rpm = 60000000 / diffTime; // calculate how many rev per minute      unsigned long currentMillis = millis();      if (currentMillis - prevMillis > interval) {
prevMillis = currentMillis;
}
showNumber(rpm);
prevTime = currentTime;
}
state2 = state1;
}
}void showNumber (int number)
{
if (number == 0)
showDigit (0, numberofDigits - 1); //display 0 in the rightmost digit
else
{
for (int digit = numberofDigits - 1; digit >= 0; digit--)
{
if (number > 0)
{
showDigit(number % 10, digit);
number = number / 10;
}
}
}
}//Displays given number on a 7-segment display at the given digit position
void showDigit (int number, int digit)
{
digitalWrite(digitPins[digit], HIGH);
for (int segment = 1; segment < 8; segment++)
{
boolean isBitSet = bitRead(numeral[number], segment);    //isBitSet= ! isBitSet; //remove this line if common cathode display
digitalWrite(segmentPins[segment], isBitSet);
}
delay(5);
digitalWrite(digitPins[digit], LOW);
}```

## Step 2: TESTING..

I test this tachometer using computer fan with attached magnet on fan blade.

Finally I put Hall Effect Sensor Module on my Mini Drill Machine, and test the sensor.

Tachometer running well.... YEAY!!

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## 7 Discussions

The print layout is faulty pin 4 of the display is not connected

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266/5000

Good work, Mr. Saftari. Do you think it is possible to implement the code to obtain an output signal based on the number of revolutions? Let me explain, I would like to get an output signal which, however, is increasingly delayed as the speed increases.

Buon lavoro, signor Saftari. Pensi che sia possibile implementare il codice per ottenere un segnale in uscita in base al numero di giri? Lasciatemi spiegare, vorrei ottenere un segnale in uscita che, tuttavia, è sempre più ritardato all'aumentare del numero di giri.

Good job Mr Saftary. Do you think it is possible to implement the code in order to obtain an output signal according to the number of laps? Let me explain, I would like to get an outgoing signal which, however, is increasingly delayed as the number of revolutions increases.

Hey, nice tutorial. What kind of 7 seg. 4 digit display did you use? Common Cathod or Common Anode? I bought a CC one and I'd like to try this project.

I've had problems getting it to work. I have tried both a nano and a promini. When connected, the segments on the display just flash in no set order. When I connect the hall effect sensor the lights go blank. The hall effector light does blink when the magnetic field goes by. I tried using 300 ohm resistor and it did the same thing.

Any suggestions?

Thanks,

Bob