Measure RPM DIY Portable Digital Tachometer

8/10/2019 Measure RPM DIY Portable Digital Tachometer

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http://www.instructables.com/id/Measure-RPM-DIY-Portable-Digital-Tachometer/

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Measure RPM - Optical Tachometerby electro18on September 17, 2014

Table of Contents

Measure RPM - Optical Tachometer ...............................................................................................

Intro: Measure RPM - Optical Tachometer ........................................................................................

File Downloads ...........................................................................................................

Step 1: Part List : ..........................................................................................................

Step 2: Build the sensor .....................................................................................................

Step 3: Making the sensor board ...............................................................................................

Step 4: The 3-pin LCD .......................................................................................................

Step 5: Make the box .......................................................................................................

Step 6: Finishing Touch ......................................................................................................

Step 7: Program ........................................................................................................... 1

Step 8: Explanation and Calculation ............................................................................................ 1

Step 9: Testing and Troubleshooting ............................................................................................ 1

Step 10: Conclusion ........................................................................................................ 1

Related Instructables ........................................................................................................ 1

Advertisements ............................................................................................................... 1

Comments ................................................................................................................ 1
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Author:electro18

Hey there ! I'm an electronic hobbyist interested in making robots and sharing stuff. I hope that my instructables help you in solving your problems HappyTinkering !

Intro: Measure RPM - Optical TachometerThis Instructable will show you how to make a Portable Digital Optical Tachometer using an Arduino Uno. This project is inspired from This instructableand is anenhanced version of it with an LCD display and a modified code.

Instead of a slotted sensor , it has a reflection based sensor. So :

1. You don't have to worry about the thickness of the rotor

2. The number of blades won't change your readings

3. It can also read the RPM of drum style rotors which slotted sensor can't

What is a tachometer ?

A tachometer is a device used to measure the RPM or Revolutions Per Minute of any rotating body. Tachometers can be contact based or non-contact ones. The noncontact or contact-less optical tachometers usually use laser or Infrared beam to monitor the rotation of any body. This is done by calculating time taken for one rotatio

FEATURESIt can measure RPM over 20k Sensor range extends upto 7~8 cm Displays Maximum RPM when left IdleAutomatically toggles modes from "Idle" to"reading"Can be adjusted to match the ambient lighting conditionsIt is comparatively cheap and easy to buildCan work without an LCDProgrammable and supportscustomization Connect an SD card to the Arduino to keep logs

File Downloads

LCD_TACHOMETER.ino(3 KB)
http://www.instructables.com/files/orig/FHK/QKDL/I07YMX7Y/FHKQKDLI07YMX7Y.ino?utm_source=pdf&utm_campaign=fileshttp://www.instructables.com/files/orig/FHK/QKDL/I07YMX7Y/FHKQKDLI07YMX7Y.ino?utm_source=pdf&utm_campaign=fileshttp://www.instructables.com/files/orig/FHK/QKDL/I07YMX7Y/FHKQKDLI07YMX7Y.ino?utm_source=pdf&utm_campaign=fileshttp://www.instructables.com/id/Arduino-Based-Optical-Tachometer/http://member/electro18/http://member/electro18/


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[NOTE: When saving, if you see .tmp as the file ext, rename it to 'LCD_TACHOMETER.ino']

Step 1:Part List :Electronics

ArduinoResistors - 33k , 270 ohm , 10k potentiometerLED - blueIR LED and Photodiode16 x 2 LCD74HC595 shift RegisterRibbon cable ( 3 wire )Perfboard and headers

Tools and Hardware

Soldering IronSolderPinsScrewsMotors and DC fan
http://www.instructables.com/files/orig/FHK/QKDL/I07YMX7Y/FHKQKDLI07YMX7Y.ino?utm_source=pdf&utm_campaign=files


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Step 2:Build the sensorFor the sensor you'll need an IR LED and a Photodiode.

1. Start by sanding the LED and photodiode to make it flat ( do not sand it too much or you'll destroy it ).

2. Then fold a strip of paper sheet as shown. Make two such Structures so that the LED and Photodiode fit tightly into it. Joint these together by glue and paint themblack.

3. Insert your LED and Photodiode in them in such a way that the positive ( longer ) lead of the LED is right above the shorter lead of the photodiode.

4. Glue them into the cover using superglue and solder the positive ( longer ) lead of the LED to the shorter lead of the photodiode.

5. Solder the 3 wire ribbon cable to the remaining leads

In my case :

1. Orange wire --> LED's positive pin and photodiode's shorter lead

2. Yellow wire --> photodiode's longer lead

3. Green Wire --> LED's ground pin

You're ready to make the board >>


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Step 3:Making the sensor boardTake a small piece of Perfboard and place the components according to the schematics.

The resistor values may vary depending on what kind of photodiode are you using.

The potentiometer helps in reducing or increasing the sensitivity of the sensor.

Finally solder the sensor wires as shown and solder 3 headers.

The headers ( in order ) are shown on the left side of the schematic.

make a cuboidal paper tube whose length is equal to the sensor wires.


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Step 4:The 3-pin LCDThis method uses a 8-bit shift register 74HC595 with a 16 x 2 LCD. Normally this LCD uses 6 pins but using a shift register reduces the pin requirement by 3.

The full instruction guide and the library can be downloaded from THIS WEBSITE!

The only thing that I've changed is :

instead of going for (2, 4, 3) configuration I've used (8, 10, 9)

So be sure to change the pin mapping accordingly
http://cjparish.blogspot.in/2010/01/controlling-lcd-display-with-shift.html


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Step 5:Make the boxYou can use any type of case for this but I've used a piece of cardboard to make enclosure.

Cut the cardboard as shown and cut appropriate sized slits for the USB port , power jack and the sensor board.

Mount the Arduino on the platform using screws.

Attach the sensor and push it through the hole.

Connect the LCD to Arduino as shown.

Close the box and paint.


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Step 6:Finishing TouchMake a small ( 5mm ) hole to fix the status LED. Solder a 270 ohm resistor to the LED and insert it into pin 12 on Arduino.

Fold the cardboard along the lines to complete the enclosure. Keep the folds in place by using pins.

Cover the sensor with a cubical paper tube to give additional mechanical strength.

Place the LCD module over the box.

Your device is ready for calibration and programming.


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Step 7:ProgramCode

COPY THIS CODE INTO YOUR ARDUINO IDE

#include

ShiftLCD lcd(8 ,10 , 9); // DEFINE LCD PINS

volatile byte REV; // VOLATILE DATA TYPE TO STORE REVOLUTIONS

unsigned long int rpm, maxRPM; // DEFINE RPM AND MAXIMUM RPM

unsigned long time; // DEFINE TIME TAKEN TO COVER ONE REVOLUTION

int ledPin = 12; // STATUS LED

int led = 0,RPMlen , prevRPM; // INTEGERS TO STORE LED VALUE AND CURRENT RPM AND PREVIOUS RPM

int flag = 0; // A VARIABLE TO DETERMINE WHETHER THE LCD NEEDS TO BE CLEARED OR NOT

long prevtime = 0; // STORE IDLE TIME TO TOGGLE MENU

void setup()

{

Serial.begin(9600); // GET VALUES USING SERIAL MONITOR

lcd.begin(16, 2); // INITIATE LCD

attachInterrupt(0, RPMCount, RISING); // ADD A HIGH PRIORITY ACTION ( AN INTERRUPT) WHEN THE SENSOR GOES FROM LOW TO HIGH

REV = 0; // START ALL THE VARIABLES FROM 0

rpm = 0;

time = 0;

pinMode(ledPin, OUTPUT);

pinMode(3, OUTPUT);

pinMode(4, OUTPUT);

digitalWrite(3, HIGH); // VCC PIN FOR SENSOR

digitalWrite(4, LOW); // GND PIN FOR SENSOR

lcd.print("TACHOMETER"); // STARTUP TEXT

lcd.setCursor(0, 1);

lcd.print("- ELECTRO18"); // THAT'S ME

delay(2000);

lcd.clear();

}

void loop()

{

long currtime = millis(); // GET CURRENT TIME

long idletime = currtime - prevtime; // CALCULATE IDLE TIME

if(REV >= 5 ) // IT WILL UPDATE AFETR EVERY 5 READINGS

{

if(flag==0) // CLEAR THE LCD TO AVOID ANY GARBAGE TEXT

{

lcd.clear();

lcd.print("SENSOR MEASURING");

flag=1; // AFTER FLAG = 1 , THE LOOP WILL NOT EXECUTE AGAIN

}

rpm = 30*1000/(millis() - time)*REV; // CALCULATE RPM USING REVOLUTIONS AND ELAPSED TIME

if(rpm > maxRPM)

maxRPM = rpm; // GET THE MAX RPM THROUGHOUT THE RUN

time = millis();

REV = 0;

int x= rpm; // CALCULATE NUMBER OF DIGITS IN RPM

while(x!=0) {

x = x/10;

RPMlen++;

}

if(RPMlen!=prevRPM) // IF THE RPM FALLS TO A LOWER NUMBER WITH LESS DIGITS , THE LCD WILL GET CLEARED

{

lcd.clear();

prevRPM = RPMlen;

flag=0;

lcd.print("SENSOR MEASURING");

}


lcd.print(rpm,DEC); // PRINT RPM IN DECIMAL SYSTEM

lcd.setCursor(6,1);


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lcd.print("RPM");

delay(500);

prevtime = currtime; // RESET IDLETIME

}

if(idletime > 5000 ) // IF THERE ARE NO READING FOR 5 SEC , THE SCREEN WILL SHOW MAX RPM

{

if(flag==1) // CLEAR THE LCD

{

lcd.clear();

flag=0;

}

lcd.clear();

lcd.print("MAXIMUM RPM");


lcd.print(maxRPM,DEC); // DISPLAY MAX RPM

lcd.print(" RPM");

delay(2000);

lcd.clear();

lcd.print("IDLE STATE");


lcd.print("READY TO MEASURE");

delay(2000);

prevtime = currtime;

}

}

void RPMCount() // EVERYTIME WHEN THE SENSOR GOES FROM LOW TO HIGH , THIS FUNCTION WILL BE INVOKED

{

REV++; // INCREASE REVOLUTIONS

if (led == LOW)

{

led = HIGH; // TOGGLE STATUS LED

}

else

{

led = LOW;

}

digitalWrite(ledPin, led);

}

////////////////////////////////////////////////////////////// END OF THE PROGRAM ///////////////////////////////////////////////////////////////

Step 8:Explanation and CalculationThis program basically monitors the IR sensor's value constantly and with the highest priority using Interrupts.

The Arduino Uno has 3 interrupts and the Interrupt 0 is pin 2 on the arduino.

attachInterrupt(0, RPMCount, RISING);

This line attaches an interrupt to pin 2 on arduino in "RISING" mode. This means that whenever the sensor goes from LOW to HIGH , the function RPMCount(); is

invoked.

This means that in one revolution , the function will be called twice ( REV++ ). Therefore actualREV = REV/ 2.

rpm = 30*1000/(millis() - time)*REV;

To calculate the actual RPM, we need the time taken for one revolution. And (millis() - time) is the time taken for one full revolutions.

In this case , let t be the time taken for one full revolution , so the total number of revolutions RPM in 60sec ( 60*1000 millisecond ) is :

rpm = 60*1000 / t * actualREV => rpm = 60*1000 / (millis() - time ) * REV/2

OR rpm = 30*1000 / (millis() - time) * REV;

Step 9:Testing and TroubleshootingTesting :

1. Take a DC fan and stick a white tape to one of it's blades. Place the sensor 2~7 cm from the blades

2. The readings will appear on the LCD

3. If the sensor gets no readings for 5 sec then it will automatically display the idle screen

4. The Idle screen will display the maximum RPM reached in that particular run.

TROUBLESHOOTING :

1. If the status LED is not blinking, try to adjust the potentiometer until the sensor is able to get readings

2. Ambient light may sometimes interfere with the sensor. Decreasing the sensitivity would eliminate the chance of getting false readings.

3. Check the polarity of the photodiode properly.

4. If everything fails , check your sensor manually by using :


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electro18says: Sep 18, 2014. 12:10 PM REPThanks a lot ! :)

BLR_RAVIsays: Sep 18, 2014. 8:22 AM REPexcellent project..very nicely and neatly made..

electro18says: Sep 18, 2014. 8:25 AM REPThanks ! :)

BeachsideHanksays: Sep 17, 2014. 3:46 PM REPI like all your stuff, so I'm following you. Just a thought-the composition of your Instructables are of course, up to you but I think yourstated mission is to share, so thechoice of fonts can be somewhat critical to those of us in the over 40 club(you've got a while before you need to worry ;-) ). Specifically, open frameand shadowing of textual descriptions tend to appear blurry, slowing down theassimilation of critical data. This in no way diminishes your noteworthyaccomplishments, but I just thought you'd like to know the perspective from theother side of the hill and in closing, congratulations on some very fine work,you will go far I do believe.

electro18says: Sep 17, 2014. 8:35 PM REPThanks for the encouragement , it means a lot to me :) and thanks for the suggestion , I'll be sure to use a better font in my next instructable.

seamstersays: Sep 17, 2014. 3:04 PM REPWow! Nicely done!

electro18says: Sep 17, 2014. 8:32 PM REPThanks ! :)
http://www.instructables.com/id/Measure-RPM-DIY-Portable-Digital-Tachometer/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/electro18/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/electro18/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/Measure-RPM-DIY-Portable-Digital-Tachometer/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/seamster/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/seamster/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/Measure-RPM-DIY-Portable-Digital-Tachometer/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/electro18/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/electro18/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/Measure-RPM-DIY-Portable-Digital-Tachometer/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/BeachsideHank/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/BeachsideHank/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/Measure-RPM-DIY-Portable-Digital-Tachometer/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/electro18/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/electro18/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/Measure-RPM-DIY-Portable-Digital-Tachometer/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/BLR_RAVI/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/BLR_RAVI/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/Measure-RPM-DIY-Portable-Digital-Tachometer/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/electro18/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/electro18/?utm_source=pdf&utm_campaign=comments

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Measure RPM DIY Portable Digital Tachometer