Clock Display With Serial - Sparkfun

Introduction

These seven segment displays are managed by an extra Arduino embedded in them. As a result, far less wiring and code is required for your project, since it is all encapsulated in this nice package. Here is the finished project:

Basic Wiring (I2C)

The wiring is really straightforward. On the top sides there is an SDA and SCL, which go to A4 and A5 respectively on your Arduino Uno. If you are using a different Arduino, check the documentation on the Wire library to see which pin you should use.

On the bottom sides, there is a plus and minus, which should be hooked up to the 5V and GND pins respectively on your Arduino.

Basic Code

I based my code on the public domain code posted by sparkfun. I added:

• Number formatting (space padded to the right)
• Use snprintf to handle overflows
• Funciton for decimal printing using floats
• Beware! Floats on Arduino are really innacurate. I get 0.01 error on just a 3 digit number!

/* Serial7Segment is an open source seven segment display. 
 To get this code to work, attach a Serial7Segment to an Arduino Uno using:
 A5 to SCL
 A4 to SDA
 VIN to PWR
 GND to GND
*/

#include <Wire.h>

#define APOSTROPHE  5
#define COLON       4
#define DECIMAL4    3
#define DECIMAL3    2
#define DECIMAL2    1
#define DECIMAL1    0

//This is the default address of the OpenSegment with both solder jumpers open
#define DISPLAY_ADDRESS1 0x71 

void setup()  {
  Wire.begin();       //Join the bus as master

  Serial.begin(9600); //Start USB serial communication at 9600 for debug prints

  //Send the reset command to the display
  //this forces the cursor to return to the beginning of the display
  Wire.beginTransmission(DISPLAY_ADDRESS1);
  Wire.write('v');
  Wire.endTransmission();
  
  //High Brightness
  Wire.beginTransmission(DISPLAY_ADDRESS1);
  Wire.write(0x7A);         // Brightness control command
  Wire.write(100);          // Set brightness level: 0% to 100%
  Wire.endTransmission();
}


float cycles = 0.0;         // TEST DECIMAL SENDING
void loop() {
  cycles+= 0.1;             // increment decimal 
  Serial.print("Cycle: ");
  Serial.println(cycles);
  
  i2cSend(cycles);          //Send the decimal to the display
  
  delay(1);                 //a very small delay to prevent flickering
}

void i2cSend(float numberToPrint) {
    int decimalPlace = -1;
    
    //find decimal place, fix the position of leftmost digit to the left
    if ( numberToPrint < 0 ) {
        i2cSend( int( numberToPrint * 100 ) );
        decimalPlace = DECIMAL1;
    }
    else if ( numberToPrint < 10 ) {
        i2cSend( int( numberToPrint * 1000 ) );
        decimalPlace = DECIMAL1;
    }
    else if ( numberToPrint < 100 ) {
        i2cSend( int( numberToPrint * 100) );
        decimalPlace = DECIMAL2;
    }
    else if ( numberToPrint < 1000 ) {
        i2cSend( int( numberToPrint * 10) );
        decimalPlace = DECIMAL3;
    }
    else {
        i2cSend( numberToPrint );
    }
    
    if ( decimalPlace != -1 ) {
        Wire.beginTransmission(DISPLAY_ADDRESS1); // transmit to device #1
        Wire.write( 0x77 );                       // send decimal command
        Wire.write( 1 << decimalPlace );          // send the place using bitshift
        Wire.endTransmission();                   // Stop I2C transmission
    }
}

//Given a number, chop up an integer into four values and sends them over I2C
void i2cSend(int numberToPrint ) {

  // use snprintf. It will align the number to the right of the string
  // snprintf truncates the number after the first few digits
  char str[5];
  snprintf(str, 5, "%4d", numberToPrint);
  
  i2cSendString( str );

  // the number is too big - mark that it was cut off.
  if ( numberToPrint > 9999 ) {
      Wire.beginTransmission(DISPLAY_ADDRESS1);   // transmit to device #1
      Wire.write( 0x77 );                         // send decimal command
      Wire.write( 1 << APOSTROPHE );              // indicate an "overflow"
      Wire.endTransmission();                     // Stop I2C transmission
  }
}

//Given a string, i2cSendString sends the first four characters over i2c
void i2cSendString(char *toSend) {
  Wire.beginTransmission(DISPLAY_ADDRESS1); // transmit to device #1
  for(byte x = 0 ; x < 4 ; x++)             // for each of the 4 characters
    Wire.write(toSend[x]);                  // Send the character from the array
  Wire.endTransmission();                   // Stop I2C transmission
}

Documentation

 Here are some other links to SparkFun's documentation:

• Product Page: https://www.sparkfun.com/products/11442
• Tutorial: http://www.sparkfun.com/tutorials/407
• Code: https://github.com/sparkfun/Serial7SegmentDisplay