Arduino GPS clock with MAX7219 driven 7 segment displays.

This is the start of an on-going time standard project.

The idea is to have three clocks, one MSF clock being received from the NPL on 60KHz, one DCF77 clock on 77.5 KHz and one GPS clock.

This is the first part of the clock, the GPS clock.

I'll be using the Ublox NEO receiver I've used before in the fast GPS-logger project here. The receiver is configured in exactly the same manner as described in that article, so pop along there and learn how to use u-center to configure your receiver.

I purchased some great MAX7219 display boards from eBay. There was a bit of a wait, as they came from China, but they were much less expensive than others, and the build quality is OK.

 Note on some board the CS pin is marked up LOAD.

I'm not going to draw a schematic, as it really is simple. (Leave me a comment if you get stuck!)
The wiring is commented in the code below.





The code is also simple, we're not doing anything particularly clever. There's a bit in the code which writes "no GPS" on the display, and this is defined as a bitmap. The bitmap refers to the segments as follows:

Bit 1(LSB) is G
Bit 2 is F
Bit 3 is E
Bit 4 is D
Bit 5 is C
Bit 6 is B
Bit 7 is A
and finally, bit 8 is the decimal point.






Here's a quick video of the clock in action:


... and here's the code:-

/*
 7-segment GPS clock 
 Version 0.9
 Written by Andy Doswell 2015
 License: The MIT License (See full license at the bottom of this file)
   
 Schematic can be found at www.andydoz.blogspot.com/
 
 You will need the LedControl library from http://playground.arduino.cc/Main/LedControl
 and the very excellent TinyGPS++ library from http://playground.arduino.cc/Main/LedControl
 
 pin 12 is connected to the DataIn 
 pin 11 is connected to the CLK 
 pin 10 is connected to CS
 pin 0 (RX)  is connected to the GPS TX pin

 */
 
#include "LedControl.h"
#include <TinyGPS++.h>

LedControl lc=LedControl(12,11,10,1); //Tells LedControl where our hardware is connected.
TinyGPSPlus gps; //TinyGPS++ class
static const uint32_t GPSBaud = 57600; //Our GPS baudrate. 
int hourTen; //tens of hours
int hourUnit; //units of hours
int minTen; // you get the idea..
int minUnit;
int secTen;
int secUnit;
int centTen; //centiseconds.
int centUnit;
unsigned long timer =0;

void setup() {

  lc.shutdown(0,false); // Wake up the MAX 72xx controller 
  lc.setIntensity(0,8); // Set the display brightness
  lc.clearDisplay(0); //Clear the display
  
  Serial.begin(GPSBaud); // start the comms with the GPS Rx
}

// This contains the bit patterns for the "no GPS" display.

void displayNoGPS() { // displays "noGPS" if the GPS lock isn't valid
  lc.setRow(0,0,B00000000);
  lc.setRow(0,1,B00000000);
  lc.setRow(0,2,B01011011);
  lc.setRow(0,3,B01100111);
  lc.setRow(0,4,B01011110);
  lc.setRow(0,5,B00000000);
  lc.setRow(0,6,B00011101);
  lc.setRow(0,7,B00010101);
}

void displayNoSerial() { // Displays "noSeriAL" in the event of serial comms fail.

  lc.setRow(0,7,B00010101);
  lc.setRow(0,6,B00011101);
  lc.setRow(0,5,B01011011);
  lc.setRow(0,4,B01001111);
  lc.setRow(0,3,B00000101);
  lc.setRow(0,2,B00010000);
  lc.setChar(0,1,'a',false);
  lc.setRow(0,0,B00001110);
}
  
// Displays the time on our LEDs
void displayTime() { 
  if (gps.time.isValid()) {
    timer = millis(); // reset the serial comms timer
    hourUnit = (gps.time.hour()%10);
    hourTen = ((gps.time.hour()/10)%10);
    minUnit = (gps.time.minute()%10);
    minTen = ((gps.time.minute()/10)%10);
    secUnit = (gps.time.second()%10);
    secTen = ((gps.time.second()/10)%10);
    secUnit = (gps.time.second()%10);
    secTen = ((gps.time.second()/10)%10);
    centUnit = (gps.time.centisecond()%10);
    centTen = ((gps.time.centisecond()/10)%10);
    lc.setDigit (0,7,hourTen,false);
    lc.setDigit (0,6,hourUnit,false);
    lc.setDigit (0,5,minTen,false);
    lc.setDigit (0,4,minUnit,false);
    lc.setDigit (0,3,secTen,false);
    lc.setDigit (0,2,secUnit,false);
    lc.setDigit (0,1,centTen,false);
    lc.setDigit (0,0,centUnit,false);
  }
  else
  {
    displayNoGPS();
    delay (2000);
  }
  
}

void loop()
{
  // If the GPS data is OK, then display it. If not display "no GPS"
  while (Serial.available() > 0)
    if (gps.encode(Serial.read())){
      displayTime();
    }
  if (millis() > timer+1000 ) // detects if the serial comms has failed.
  {
    displayNoSerial();
  }
  


  
}

/*
 * Copyright (c) 2015 Andrew Doswell
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHOR(S) OR COPYRIGHT HOLDER(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */