Published July 18, 2019 © GPL3+

Sorting Resistors the Lazy Way

A small device that will help you sorting resistors without wasting time with their color code.

IntermediateFull instructions provided2 hours23,927

Things used in this project

Hardware components

Arduino Nano R3

Resistor 10k ohm

Resistor 1k ohm

Resistor 100 ohm

Resistor 100k ohm

Resistor 1M ohm

ElectroPeak 0.96" OLED 64x128 Display Module

Jumper wires (generic)

Software apps and online services

Arduino IDE

Hand tools and fabrication machines

3D Printer (generic)

Soldering iron (generic)

Story

Hey there,

Are you tired of ending up after every finished project in a situation like this?

Bunch of unsorted resistors.

Are you a messy guy that's too lazy to check the color code on every resistor to sort them by resistance? Are you so lazy that even using a multimeter is too much? Than maybe there could be a solution for you, the ultimate lazy ohmmeter!

The ultimate device for lazy tinkerer.

All you will need to build this simple ohmmeter that will check the value of your unsorted resistance are a bunch of resistors (known value this time), an Arduino and a display (I used an I2C OLED display for mine).

We will then rely on the voltage divider equation in order to obtain the value of an unknown resistor in series with a resistor with a known value. This simple technique has just one drawback. The more the two resistors are different, the less accurate will be our measurement. In order to overcome this phenomena we will need to use multiple resistors and write a code that will allow the Arduino to choose the most suitable resistor for the unknown value calculation.

Following this philosophy we can build the Ohmmeter following the schematics in the image below.

Schematics of the device.

If you use an I2C display, you can also follow the schematics for that. Arduino Nano uses pin A4 for SDA and A5 for SCL.

Let's now focus on the coding part. The code I used can be seen here:

#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
  
[...]
  
int R1 = 100;
int R2 = 1000;
int R3 = 10000;
long R4 = 100000;
long R5 = 1000000;
long Rn;
int D2 = 2;
int D3 = 3;
int D4 = 4;
int D5 = 5;
int D6 = 6;
float raw = 0;
float Vout = 0;
float Ru = 0;
int Analogohm = A0;
void setup() {
 [...]
}
void loop() {
   pinMode(D2, OUTPUT);
   pinMode(D3, INPUT);
   pinMode(D4, INPUT);
   pinMode(D5, INPUT);
   pinMode(D6, INPUT);
   digitalWrite(D2, HIGH);
   raw = analogRead(Analogohm);
   Serial.println(raw);
   Serial.println("ref 1M");
   Rn = R5;
   if (raw < 350 || raw > 800){
     digitalWrite(D2, LOW);
     pinMode(D2, INPUT);
     pinMode(D3, OUTPUT);
     digitalWrite(D3, HIGH);
     raw = analogRead(Analogohm);
     Serial.println(raw);
     Serial.println("ref 100k");
     Rn = R4;
     if (raw < 350 || raw > 800){
       digitalWrite(D3, LOW);
       pinMode(D3, INPUT);
       pinMode(D4, OUTPUT);
       digitalWrite(D4, HIGH);
       raw = analogRead(Analogohm);
       Serial.println(raw);
       Serial.println("ref 10k");
       Rn = R3;
       if (raw < 350 || raw > 800){
         digitalWrite(D4, LOW);
         pinMode(D4, INPUT);
         pinMode(D5, OUTPUT);
         digitalWrite(D5, HIGH);
         raw = analogRead(Analogohm);
         Serial.println(raw);
         Serial.println("ref 1000");
         Rn = R2;
         if (raw < 350 || raw > 800){
           digitalWrite(D5, LOW);
           pinMode(D5, INPUT);
           pinMode(D6, OUTPUT);
           digitalWrite(D6, HIGH);
           raw = analogRead(Analogohm);
           Serial.println(raw);
           Serial.println("ref 100");
           Rn = R1;
         }
       }
     }
   }
   Vout = 5*(raw/1024);
   Ru = (Rn*Vout)/(5-Vout);
   if (Ru < 10 || Ru < 70) {
     Ru = 10 *round(Ru/10);
   } else if (Ru < 100 || Ru < 700){
     Ru = 100 *round(Ru/100);
   } else if (Ru < 1000 || Ru < 7000){
     Ru = 1000 *round(Ru/1000);
   } else if (Ru < 10000 || Ru < 70000){
     Ru = 10000 *round(Ru/10000);
   } else if (Ru < 100000 || Ru < 700000){
     Ru = 100000 *round(Ru/100000);
   } else if (Ru < 1000000 || Ru < 7000000){
     Ru = 1000000 *round(Ru/1000000);
   }
   Resistance(Ru);
   delay(1000);
}
[...]

For the OLED screen, I just used the Adafruit library. You just need to download that through the Library Manager of the Arduino IDE and copy the code you need. I used two bitmap just to make more fancy the reading, you can easily add your bitmap or replace the one I added.

For the ohmmeter part, you will instead need to understand how this works since you can change it dependently on how many resistors you are using as reference values.

Once the code enters the void loop, the Arduino will check the voltage on pin A0. Since from the voltage divider equation:

V0 = Vi*R2/(R1+R2)

If R1 and R2 are the same, we should have V0 close to 2.5V (thus 512 on our 10 bits reading).

If the value is far from these results, then the code moves to the next value and so forth until we get the closest resistor. One the "close resistance" condition is fulfilled, the value will be printed on the display.

NOTE #1: On each IF statement we need to redefine the pinMode of every digital pin, since if you keep that as output it will behave as a low impedance pin and screw up our measurement on pin A0.

Once the right resistor has been selected, the unknown resistor value ( Ru variable inside the code) is calculated using the voltage divider equation.

NOTE #2: For this device I used just 5 resistors, but if you like you can have way more values for each digital pin on the board.

The photo below the system built on a breadboard.

Lazy meter on a breadboard.

Now for the real application, we will need to build some kind of box where we can plug in the unknown resistor and the result will be shown on the screen.

The box I made can be easily printed with a 3D printer and all parts can be fixed together with a glue gun. Some soldering of the known resistors was required in order to make everything fit in a small volume.

Final device.

Just one thing left: plug your unsorted resistors in those tiny holes and clean your workbench!

Have fun and see you in the next tutorial.

EDIT: I modified the rounding part of the code since as it was it could cause error while rounding around 5k resistors. With this change the problem should be solved. Anyway adding a 5k resistor among the references should prevent the problem at all.

Schematics

Code

Lazy R meter code

#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128 // OLED display width, in pixels
#define SCREEN_HEIGHT 64 // OLED display height, in pixels

// Declaration for an SSD1306 display connected to I2C (SDA, SCL pins)
#define OLED_RESET     4 // Reset pin # (or -1 if sharing Arduino reset pin)
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

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};

const unsigned char myBitmap [] PROGMEM = {
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  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x07, 0xe0, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x3f, 0x60, 0x00, 0x00, 0x01, 0xf8, 0x18, 0x00, 0x00, 0x00, 
  0x00, 0x07, 0x80, 0x00, 0x00, 0x07, 0x80, 0x18, 0x00, 0x00, 0x03, 0xc0, 0x06, 0x00, 0x00, 0x00, 
  0x01, 0xf8, 0x60, 0x00, 0x00, 0x00, 0xf8, 0x0c, 0x00, 0x00, 0x00, 0x1f, 0x07, 0x00, 0x00, 0x00, 
  0x0f, 0x80, 0x18, 0x00, 0x00, 0x00, 0x0f, 0x03, 0x80, 0x00, 0x00, 0x07, 0x00, 0xc0, 0x00, 0x00, 
  0x00, 0x7c, 0x1c, 0x00, 0x00, 0x00, 0x03, 0xe0, 0xe0, 0x00, 0x00, 0x00, 0xf0, 0x38, 0x00, 0x00, 
  0x00, 0x1e, 0x03, 0x80, 0x00, 0x00, 0x00, 0x3c, 0x60, 0x00, 0x00, 0x00, 0x0e, 0x38, 0x00, 0x00, 
  0x00, 0x03, 0xe0, 0xe0, 0x00, 0x00, 0x00, 0x0f, 0x9c, 0x00, 0x00, 0x00, 0x07, 0xc6, 0x00, 0x00, 
  0x00, 0x00, 0x38, 0x60, 0x00, 0x00, 0x00, 0x00, 0x3f, 0x80, 0x00, 0x00, 0x00, 0x3f, 0xc0, 0x00, 
  0x00, 0x00, 0x07, 0x9c, 0x00, 0x00, 0x00, 0x00, 0x00, 0xc0, 0x00, 0x00, 0x00, 0x00, 0xf0, 0x00, 
  0x00, 0x00, 0x00, 0x3f, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0xc0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};


int R1 = 100;
int R2 = 1000;
int R3 = 10000;
long R4 = 100000;
long R5 = 1000000;
long Rn;
int D2 = 2;
int D3 = 3;
int D4 = 4;
int D5 = 5;
int D6 = 6;

float raw = 0;
float Vout = 0;
float Ru = 0;
int Analogohm = A0;

void setup() {
  Serial.begin(9600);

  
  if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) { 
    Serial.println(F("SSD1306 allocation failed"));
    for(;;); 
  }
  display.clearDisplay();
  display.drawBitmap(0,0, myLOGO, 128, 64, WHITE);
  display.display();
  delay(2000);
}


void loop() {

    pinMode(D2, OUTPUT);
    pinMode(D3, INPUT);
    pinMode(D4, INPUT);
    pinMode(D5, INPUT);
    pinMode(D6, INPUT);

    digitalWrite(D2, HIGH);
    raw = analogRead(Analogohm);
    Serial.println(raw);
    Serial.println("ref 1M");
    Rn = R5;

    if (raw < 350 || raw > 800){
      digitalWrite(D2, LOW);
      pinMode(D2, INPUT);
      pinMode(D3, OUTPUT);
      digitalWrite(D3, HIGH);
      raw = analogRead(Analogohm);
      Serial.println(raw);
      Serial.println("ref 100k");
      Rn = R4;

      if (raw < 350 || raw > 800){
        digitalWrite(D3, LOW);
        pinMode(D3, INPUT);
        pinMode(D4, OUTPUT);
        digitalWrite(D4, HIGH);
        raw = analogRead(Analogohm);
        Serial.println(raw);
        Serial.println("ref 10k");
        Rn = R3;

        if (raw < 350 || raw > 800){
          digitalWrite(D4, LOW);
          pinMode(D4, INPUT);
          pinMode(D5, OUTPUT);
          digitalWrite(D5, HIGH);
          raw = analogRead(Analogohm);
          Serial.println(raw);
          Serial.println("ref 1000");
          Rn = R2;

          if (raw < 350 || raw > 800){
            digitalWrite(D5, LOW);
            pinMode(D5, INPUT);
            pinMode(D6, OUTPUT);
            digitalWrite(D6, HIGH);
            raw = analogRead(Analogohm);
            Serial.println(raw);
            Serial.println("ref 100");
            Rn = R1;
          }
        }
      }
    }

    Vout = 5*(raw/1024);
    Ru = (Rn*Vout)/(5-Vout);
    if (Ru < 10 || Ru < 70) {
      Ru = 10 *round(Ru/10);
    } else if (Ru < 100 || Ru < 700){
      Ru = 100 *round(Ru/100);
    } else if (Ru < 1000 || Ru < 7000){
      Ru = 1000 *round(Ru/1000);
    } else if (Ru < 10000 || Ru < 70000){
      Ru = 10000 *round(Ru/10000);
    } else if (Ru < 100000 || Ru < 700000){
      Ru = 100000 *round(Ru/100000);
    } else if (Ru < 1000000 || Ru < 7000000){
      Ru = 1000000 *round(Ru/1000000);
    }
    Resistance(Ru);
    delay(1000);
}

void Resistance(long Ru) {
  display.clearDisplay();

  display.setTextSize(1);            
  display.setTextColor(WHITE);        
  display.setCursor(0,0);             
  display.println(F("Hey there, "));
  display.println(F("the Resistor value is"));
  display.setCursor(20,25);
  display.setTextSize(2);             
  display.setTextColor(WHITE);        
  display.print(Ru);
  display.print(F(" Ohm"));
  display.drawBitmap(0,0, myBitmap, 128, 64, WHITE);
  display.display();
  delay(2000);
}

Credits

Federico Vivaldi

4 projects • 35 followers

I'm a PhD student in chemistry and material science. I use my hobby in simple electronic to build items for laboratory.

Sorting Resistors the Lazy Way

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

Custom parts and enclosures

Top part

Bottom part

Schematics

Lazy meter schematics

Code

Lazy R meter code

Credits

Federico Vivaldi

Comments

Embed the widget on your own site

Sorting Resistors the Lazy Way

Sorting Resistors the Lazy Way

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

Custom parts and enclosures

Top part

Bottom part

Schematics

Lazy meter schematics

Code

Lazy R meter code

Credits

Federico Vivaldi

Comments

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