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)

Connect These Pins:
ArduinoSerial7Segment
A5 SCL
A4 SDA
5V +
GND -

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)
  • 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: