Arduino Volt-Ammeter - Part 1 - Breadboard

I was looking for a real device project to get out from "blinking leds" of Arduino's tutorials and build a device that could be useful in some way. I always thought confuse to have to use two voltmeters, besides the excess of wires around, I already burnt almost all current scales from my voltmeters, to measure current and voltage simultaneously.

Versão em português desse artigo: Volt-Amperímetro com Arduino - Parte 1: Protoboard.

This project is based on model described in PIC Volt Ampere Meter. I thought that his project was viable, but I would need a PIC programmer and make all source code by hand, since they prefer don't disclose many project details in order to create interest in people in purchase their full assembly kit. As I already had an Arduino, I decided use it as prototyping and programming platform and then write the code by myself. Finally, the only advantages taken from the PIC model was the usage of shunt resistor in current measurement and the idea for a calibration mode, since the total circuit resistances could not be entirely predictable even when using 1% precision resistors.

The component list to build this breadboard project is:

• 1 Arduino;
• 1 Breadboard (don't forget the jumper wires);
• 1 Display 1602A (16x2 with backlight);
• 1 1x16 break away headers for display fixing;
• 1 Buzzer;
• 2 Screw terminals with 2 pins each one;
• 3 Tactile switches (buttons);
• 1 10k potentiometer;
• 6 10k resistors;
• 2 100k resistors;
• 1 100R resistor;
• 1 10R resistor;
• 1 0.47R 5W power resistor.

The components must be assembled in breadboard as following:

For those who yet don't  know, the application used to create this breadboard schema was Fritzing. It's free and very easy to use. Click here to download the Fritzing source file for this project.

Bellow the Arduino sketch source code:

//version
#define NAME "Arduino Ammeter"
#define VERSION "0.9"

//debug flag (avoid enabling. it makes your device slower)
//#define DEBUG

//pins
const int PIN_BACKLIGHT = 7;
const int PIN_BUZZER = 3;
const int PIN_VOLTAGE = 0;
const int PIN_CURRENT = 1;
const int PIN_BUTTON_UP = 6;
const int PIN_BUTTON_SETUP = 5;
const int PIN_BUTTON_DOWN = 4;

// includes
#include <LiquidCrystal.h>
#include <EEPROM.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(13, 12, 11, 10, 9, 8);

//variables
//voltage
int VOLTAGE_CURRENT;
int VOLTAGE_LAST=99999;
unsigned long VOLTAGE_MILLIS;
float VOLTAGE_CALCULATED;
float VOLTAGE_MAP = 50; //default voltage map... calibration needed
//current
int CURRENT_CURRENT;
int CURRENT_LAST=99999;
unsigned long CURRENT_MILLIS;
float CURRENT_CALCULATED;
float CURRENT_MAP = 10; //default current map... calibration needed 
//buttons
boolean BUTTON_PRESSED = false;
unsigned long BUTTON_MILLIS = false;
byte BUTTON_LAST;
boolean SETUP_MODE = false;
byte SETUP_ITEM;
boolean SETUP_DELAYBEEP;
//...
unsigned long MILLIS;
unsigned long SETUP_BLINKMILLIS;
boolean SETUP_BLINKSTATE;

//parameters
const int SENSOR_INTERVAL = 500;
const int BUTTON_HOLDTIME = 2000;
const int SETUP_MAXITEMS = 2;
const int SETUP_BLINKINTERVAL = 300;
const byte EEPROM_VALIDATOR = 73; //random number
const float VOLTAGE_STEP = 0.1;
const float CURRENT_STEP = 0.1;

//configuration
const byte EEPROM_CONFIGADDRESS = 0;
struct config_t
{
  byte Validator;
  /////////////////////
  float VOLTAGE_MAP;
  float CURRENT_MAP;
  /////////////////////
  byte ValidatorX2;
} EEPROM_DATA;

void setup() {
  //configure pins
  pinMode(PIN_BACKLIGHT, OUTPUT);
  pinMode(PIN_BUZZER, OUTPUT);
  pinMode(PIN_VOLTAGE, INPUT);
  pinMode(PIN_CURRENT, INPUT);
  pinMode(PIN_BUTTON_UP, INPUT);
  pinMode(PIN_BUTTON_SETUP, INPUT);
  pinMode(PIN_BUTTON_DOWN, INPUT);

  //set up LCD
  lcd.begin(16, 2);

  //initial message  
  lcd.setCursor(0, 0);
  lcd.print(NAME);
  lcd.setCursor(0, 1);
  lcd.print("Version ");
  lcd.print(VERSION);
  
  //lights up
  digitalWrite(PIN_BACKLIGHT, HIGH);
  
#ifdef DEBUG
  delay(2000);
  lcd.setCursor(0, 1);
  lcd.print("Debug enabled!  ");
  lcd.print(VERSION);

  Serial.begin(9600);
  Serial.println("============================");
  Serial.println(NAME);
  Serial.println("Version ");
  Serial.println(VERSION);
  Serial.println("============================");
  Serial.println("Debug messages:");
  Serial.println("----------------------------");
#endif
  
  //try to load the configuration
  loadConfiguration();

  //show initial message for a while then clear and beep
  delay(2000);
  lcd.clear();
  showLabels();
  
  //beep
  beepStart();
}

void loop() {
  processButtons();
  
  MILLIS = millis();

  if ( (MILLIS - VOLTAGE_MILLIS) >= SENSOR_INTERVAL )
  {
    readVoltage();
    
    if (!SETUP_MODE || SETUP_ITEM!=1) {
      showVoltage();
    }

    VOLTAGE_MILLIS = MILLIS;
  }

  if ( (MILLIS - CURRENT_MILLIS) >= SENSOR_INTERVAL )
  {
    readCurrent();
    
    if (!SETUP_MODE || SETUP_ITEM!=2) {
      showCURRENT();
    }

    CURRENT_MILLIS = MILLIS;
  }

  if (SETUP_MODE)
  {
    if ( (MILLIS - SETUP_BLINKMILLIS) >= SETUP_BLINKINTERVAL )
    {
      if (SETUP_BLINKSTATE)
      {
        if (SETUP_ITEM==1)
          showVoltage();
        else if (SETUP_ITEM==2)
          showCURRENT();
        
        SETUP_BLINKSTATE = false;
      } else {
        if (SETUP_ITEM==1)
          hideVoltage();
        else if (SETUP_ITEM==2)
          hideCURRENT();        
        
        SETUP_BLINKSTATE = true;
      }
      
      SETUP_BLINKMILLIS = MILLIS;
    }
  }
}

void processButtons()
{
  if (digitalRead(PIN_BUTTON_UP) == HIGH)
  {
    if (!BUTTON_PRESSED)
    {
#ifdef DEBUG  
      showDebug("Pressed UP");
#endif

      BUTTON_LAST = PIN_BUTTON_UP;
      BUTTON_PRESSED = true;
    }
  }
  else if (digitalRead(PIN_BUTTON_SETUP) == HIGH)
  {
    if (!BUTTON_PRESSED)
    {
#ifdef DEBUG  
      showDebug("Pressed SETUP");
#endif
      
      beepButton();
      BUTTON_LAST = PIN_BUTTON_SETUP;
      BUTTON_MILLIS = millis();
      BUTTON_PRESSED = true;
      SETUP_DELAYBEEP = false;
    } else {
      if ((millis() - BUTTON_MILLIS) > BUTTON_HOLDTIME)
        if (!SETUP_DELAYBEEP)
        {
          beepButton();
          SETUP_DELAYBEEP = true;
        }
      
    }
  }
  else if (digitalRead(PIN_BUTTON_DOWN) == HIGH)
  {
    if (!BUTTON_PRESSED)
    {
#ifdef DEBUG  
      showDebug("Pressed DOWN");
#endif 
      
      BUTTON_LAST = PIN_BUTTON_DOWN;
      BUTTON_PRESSED = true;

    }
  }
  else 
  {
    if (BUTTON_PRESSED) {
      if (BUTTON_LAST == PIN_BUTTON_SETUP)
      {
#ifdef DEBUG  
        showDebug("Released SETUP");
#endif
        
        if (!SETUP_MODE && (millis() - BUTTON_MILLIS) > BUTTON_HOLDTIME) {
#ifdef DEBUG  
          showDebug("Entered setup mode!");
#endif
          
          lcd.setCursor(0, 1);
          lcd.print("   Setup Mode   ");
          SETUP_MODE = true;
          SETUP_ITEM = 1;
        } 
        else {
          if (SETUP_ITEM == SETUP_MAXITEMS) {
#ifdef DEBUG  
          showDebug("Exited setup mode!");
#endif
            
            showLabels();
            SETUP_MODE = false;
            SETUP_ITEM = 0;
            saveConfiguration();
          } 
          else {
            SETUP_ITEM++;
          }
          
          showVoltage();
          showCURRENT();
        }
      } 
      else if (BUTTON_LAST == PIN_BUTTON_UP) {
#ifdef DEBUG  
        showDebug("Released UP");
#endif
        
        if (SETUP_MODE) {
          beepButton();
          
          if (SETUP_ITEM==1) { //voltage
            VOLTAGE_MAP+=VOLTAGE_STEP;
            readVoltage();
            
#ifdef DEBUG  
            startDebug("New VOLTAGE_MAP: ");
            Serial.println(VOLTAGE_MAP,6);
#endif
          } else if (SETUP_ITEM==2) { //current
            CURRENT_MAP+=CURRENT_STEP;
            readCurrent();
            
#ifdef DEBUG  
            startDebug("New CURRENT_MAP: ");
            Serial.println(CURRENT_MAP,6);
#endif
          }
        }
      } 
      else if (BUTTON_LAST == PIN_BUTTON_DOWN) {
#ifdef DEBUG  
        showDebug("Released DOWN");
#endif
        
        if (SETUP_MODE) {
          beepButton();
          
          if (SETUP_ITEM==1) { //voltage
            VOLTAGE_MAP-=VOLTAGE_STEP;
            readVoltage();
            
#ifdef DEBUG  
            startDebug("New VOLTAGE_MAP: ");
            Serial.println(VOLTAGE_MAP,6);
#endif
          } else if (SETUP_ITEM==2) { //current
            CURRENT_MAP-=CURRENT_STEP;
            readCurrent();
            
#ifdef DEBUG  
            startDebug("New CURRENT_MAP: ");
            Serial.println(CURRENT_MAP,6);
#endif
          }
        }
      }

      BUTTON_PRESSED = false;
    }
  }
}

#ifdef DEBUG  
void showDebug(char* Message)
{
  Serial.print(millis());
  Serial.print(": ");
  Serial.println(Message);
}

void startDebug(char* Message)
{
  Serial.print(millis());
  Serial.print(": ");
  Serial.print(Message);
}
#endif

void showLabels()
{
  lcd.setCursor(0, 1);
  lcd.print("Volts       Amps");
}

void showVoltage()
{
    lcd.setCursor(0, 0);
    lcd.print(VOLTAGE_CALCULATED, 2);
    lcd.print(" V");

    if (VOLTAGE_CALCULATED<10)
      lcd.print(" ");
}

void hideVoltage()
{
    lcd.setCursor(0, 0);
    lcd.print("       ");
}

void showCURRENT()
{
    lcd.setCursor(9, 0);

    if (CURRENT_CALCULATED<10)
      lcd.print(" ");

    lcd.print(CURRENT_CALCULATED, 2);
    lcd.print(" A");
}

void hideCURRENT()
{
    lcd.setCursor(9, 0);
    lcd.print("       ");
}

void beepStart()
{
  for (int i=0; i<300; i++) {
    digitalWrite(PIN_BUZZER, HIGH);
    delayMicroseconds(200);
    digitalWrite(PIN_BUZZER, LOW);
    delayMicroseconds(200);
  } 
}

void beepButton()
{
  for (int i=0; i<20; i++) {
    digitalWrite(PIN_BUZZER, HIGH);
    delayMicroseconds(700);
    digitalWrite(PIN_BUZZER, LOW);
    delayMicroseconds(700);
  } 
}

void readVoltage()
{
  VOLTAGE_CURRENT = analogRead(PIN_VOLTAGE);
  if ( VOLTAGE_CURRENT != VOLTAGE_LAST || SETUP_MODE ) {
    VOLTAGE_LAST = VOLTAGE_CURRENT;
    VOLTAGE_CALCULATED = fmap(VOLTAGE_CURRENT, 0, 1023, 0.0, VOLTAGE_MAP);
    
#ifdef DEBUG  
    if (!SETUP_MODE)
    {
      startDebug("New voltage: ");
      Serial.print(VOLTAGE_CALCULATED);
      Serial.println("V");
    }
#endif
  }
}

void readCurrent()
{
  CURRENT_CURRENT = analogRead(PIN_CURRENT);
  if ( CURRENT_CURRENT != CURRENT_LAST || SETUP_MODE ) {
    CURRENT_LAST = CURRENT_CURRENT;
    CURRENT_CALCULATED = fmap(CURRENT_CURRENT, 0, 1023, 0.0, CURRENT_MAP);
    
#ifdef DEBUG
    if (!SETUP_MODE)
    {
      startDebug("New current: ");
      Serial.print(CURRENT_CALCULATED);
      Serial.println("A");
    }
#endif
  }
}


float fmap(float x, float in_min, float in_max, float out_min, float out_max)
{
  return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}

int EEPROM_writeConf()
{
    byte Address = EEPROM_CONFIGADDRESS;
  
    const byte* p = (const byte*)(const void*)&EEPROM_DATA;
    int i;
    for (i = 0; i < sizeof(EEPROM_DATA); i++)
      EEPROM.write(Address++, *p++);
    return i;
}

int EEPROM_readConf()
{
    byte Address = EEPROM_CONFIGADDRESS;
  
    byte* p = (byte*)(void*)&EEPROM_DATA;
    int i;
    for (i = 0; i < sizeof(EEPROM_DATA); i++)
      *p++ = EEPROM.read(Address++);
    return i;
}

void loadConfiguration()
{
  //read data from eeprom
  EEPROM_readConf();
  
  //verify validators
  if (EEPROM_DATA.Validator == EEPROM_VALIDATOR && EEPROM_DATA.ValidatorX2 == EEPROM_VALIDATOR*2)
  {
    //copy data
    VOLTAGE_MAP = EEPROM_DATA.VOLTAGE_MAP;
    CURRENT_MAP = EEPROM_DATA.CURRENT_MAP;

#ifdef DEBUG
    showDebug("Configuration loaded from EEPROM!");
    startDebug("   VOLTAGE_MAP: ");
    Serial.println(VOLTAGE_MAP,6);
    startDebug("   CURRENT_MAP: ");
    Serial.println(CURRENT_MAP,6);
#endif
  } else {
#ifdef DEBUG
    showDebug("Configuration NOT loaded from EEPROM!");
#endif    
  }
}

void saveConfiguration()
{
  if ( EEPROM_DATA.VOLTAGE_MAP != VOLTAGE_MAP ||
       EEPROM_DATA.CURRENT_MAP != CURRENT_MAP
  ) {
    //copy validators
    EEPROM_DATA.Validator = EEPROM_VALIDATOR;
    EEPROM_DATA.ValidatorX2 = EEPROM_VALIDATOR*2;
  
    //copy data
    EEPROM_DATA.VOLTAGE_MAP = VOLTAGE_MAP;
    EEPROM_DATA.CURRENT_MAP = CURRENT_MAP;
  
    //save data to eeprom
    EEPROM_writeConf();
    
#ifdef DEBUG
    showDebug("Configuration saved!");
#endif
  } else {
#ifdef DEBUG
    showDebug("Configuration not changed!");
#endif 
  }
}

Note that at beginning of code there is a DEBUG constant definition. Uncomment this line will activate event warnings that can be monitored through Arduino Serial Monitor. This feature could help in beadboard assembly and source code debugging, however, besides write a much larger sketch in microcontroller, it will also make the software considerably slower because serial ports has a fixed speed that is considerably low. So leaving this feature enabled unnecessarily is not recommended.

The 3 buttons are used for calibration. The center button is the configuration one and it activates the calibration mode if pressed for 2 seconds, confirmed by a beep. During the coding, I had the impression that it does not properly calculate the time, then I judged interesting to have a second beep to confirm this 2 seconds taking their own time to calculate. The other buttons on left and right are to decrease and increase the calibration respectively, followed by one beep. The calibration starts with voltage, then pressing the configuration button again switches to current and when pressed again saves the configuration to EEPROM and turn the device back to normal mode.

See the continuation of this article at: Final Part - Printed circuit board