Doz' Blog: Arduino GPS master clock with 433/315 MHz transmitter

I've got a few clock projects in the back of my mind, and this is a bit of an aside to them all. I also wish to upgrade the Astronomical clock project, as the DS1307 often drifts about, losing and gaining seconds as it feel like it...

The idea is to have a master clock, GPS locked with built in 433 MHz transmitter, which will send an accurate time signal to the other clocks to bring them into sync. The transmitter will be triggered randomly, at least once every 24 hours, or by a push button connected to pin 12.

I'll be re-using the code from the quick and dirty 7-segment GPS clock here, and some of the code for the transmit function from the dehumidifier project.

I've added a 4x20 LCD display, with I2C piggyback interface board, and the u-blox GPS module we've used in the GPS logger.

The GPS module will be configured by the sketch itself, to 200mS refresh rate.

There's two sketches, the GPS clock itself, and a simple test receiver sketch to check everything's working as it should.

The I2C display is a generic display, purchased from eBay, and uses the PCF8574 I2C receiver IC. I tried a couple of different libraries, but eventually settled with the library from https://bitbucket.org/fmalpartida/new-liquidcrystal/downloads which works well with my display.
Well also use the virtual wire library to handle our comms, https://www.pjrc.com/teensy/td_libs_VirtualWire.html and the most excellent TinyGPS++ http://arduiniana.org/libraries/tinygpsplus/

There's an LED connected to pin 9, which blinks on and off every time the seconds are updated.

Here's the schematic...

... and the hardware lashed up for testing.

The second arduino is acting as our test receiver. There's no RF module in there as yet.. It's coupled to the clock arduino, GND is coupled, and pin 10 on the clock is connected to pin 9 on the receiver board. It's also supplying 5V to the other board.

Here's the data being displayed. Date (in UK format DD/MM/YYYY) , UTC time, latitude, longitude, no of satellites in use, horizontal dilution of precision and the number of seconds until the next transmission.

Here's the output from our terminal window, connected to the receiver board, showing the time and date are being correctly received when A3 is pulled to ground.

So, the final build looks like this...

You can see the antenna is simply a straight piece of wire, 173mm long (for 433 MHz modules, other frequencies will need a different length)

And assembled. Managed to cut the right sized hole for the display for once!

Here's the GPS receiver, which I'm going to mount remotely on the roof, so it get's good reception. I've stuck it into of a water-proof IP rated box, and fitted a Buccaneer connector.

OK, so to the code....

This is the transmitter code:

/*
  GPS Master clock
  (C) Andy Doswell 22nd July 2016
  License: The MIT License (See full license at the bottom of this file)

Schematic can be found at www.andydoz.blogspot.com/

Uses the very excellent TinyGPS++ library from http://arduiniana.org/libraries/tinygpsplus/
  and also the fabulous Virtualwire library from https://www.pjrc.com/teensy/td_libs_VirtualWire.html
  and the most superb I2C LCD library from https://bitbucket.org/fmalpartida/new-liquidcrystal/downloads

pin 0 (RX)  is connected to the GPS TX pin.
  A3 is connected to a "push to transmit" button.
  Pin 10 is connected to the transmitter (433MHz or whatever's legal in your area)
  LCD is a 20 x 4 I2C display fitted with PCF8574 IC

Sketch transmits a clock signal at a random time (never more than 24 hours) to sync up other clocks.

*/
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <TinyGPS++.h>
#include <VirtualWire.h>
#include <VirtualWire_Config.h>

LiquidCrystal_I2C  lcd(0x3f, 2, 1, 0, 4, 5, 6, 7); // I2C addreSerial 0x3f, 20x4 display
TinyGPSPlus gps; //TinyGPS++ claSerial
static const uint32_t GPSBaud = 9600; //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;
unsigned long transmitTimer;
unsigned long secsPastMidnight;
unsigned long SerialTimeout = 0;
unsigned long secsToMidnight;
unsigned long timerPrint;
boolean displayLoop = false;

struct TXData
{
  int TX_ID;
  int Hours;
  int Mins;
  int Secs;
  int Day;
  int Month;
  int Year;
};

void setup() {

Serial.begin(GPSBaud); // start the comms with the GPS Rx
  transmitTimer = random(0, 86399); // transmit sometime in the next 24 hours
  lcd.begin(20, 4); // set up the LCD as 20 x 4 display
  lcd.setBacklightPin(3, POSITIVE);
  lcd.setBacklight(HIGH);
  lcd.clear();
  // Virtualwire setup
  vw_set_tx_pin(10); // TX pin set to 10
  vw_set_rx_pin(9); // RX pin set to a spare pin, even though we don't use it.
  vw_setup(1200); //sets virtualwire for a tx rate of 1200 bits per second
  pinMode (A3, INPUT); // push to transmit connected to A3 and GND
  digitalWrite (A3, HIGH); // A3 pulled high
  randomSeed(analogRead(A0));
  transmitTimer = random(0, 86399); // set a random transmit time.
}

void displayData() {

SerialTimeout = millis();
  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);

if (displayLoop == false) { // this bit of code is to overcome a bit of an odd bug, and I don't know why it happens,
    lcd.setCursor (0, 1);   // but Satellites in view and HDOP return 0 if you get them along with location, regardless of order. So we only update the position every 100 cycles.
    lcd.print("  ");
    lcd.print (gps.location.lat(), 4);
    lcd.print (" ");
    lcd.print (gps.location.lng(), 4);
    lcd.print ("   ");
    displayLoop = true;
  }
  else {
    lcd.setCursor (0, 2);
    lcd.print ("  Sat:");
    lcd.print (gps.satellites.value());
    lcd.print (" HDOP:");
    lcd.print (gps.hdop.value());
    lcd.print (" ");
    displayLoop = false;
  }
  lcd.setCursor(0, 0);
  lcd.print (" ");
  lcd.print(gps.date.day());
  lcd.print("/");
  lcd.print(gps.date.month());
  lcd.print("/");
  lcd.print(gps.date.year());
  lcd.print(" ");
  lcd.print(hourTen);
  lcd.print(hourUnit);
  lcd.print(":");
  lcd.print(minTen);
  lcd.print (minUnit);
  lcd.print (":");
  lcd.print (secTen);
  lcd.print (secUnit);
  lcd.setCursor (0, 3);
  lcd.print ("    TX in:");

lcd.print (timerPrint);
  lcd.print (" ");

}

void displayNoSerial() {
  lcd.clear();
  lcd.print ("ERROR");
  lcd.setCursor (0, 1);
  lcd.print ("Serial data comms");
  lcd.setCursor (0, 2);
  lcd.print ("Check cable");
  delay (2000);
}

void displayNoGPS() {
  lcd.clear();
  lcd.print("Warning");
  lcd.setCursor(0, 1);
  lcd.print("No or poor GPS data");
  lcd.setCursor(0, 2);
  lcd.print("Sats in view=");
  lcd.print (gps.satellites.value());
}

void transmitTime () { // transmits the current time and date.

struct TXData payload; //Loads the Data struct with the payload data
  lcd.clear ();
  lcd.print ("Transmitting clock sync");
  lcd.setCursor (0, 1);
  payload.TX_ID = 1;
  payload.Hours = gps.time.hour();
  payload.Mins = gps.time.minute();
  payload.Secs = gps.time.second();
  payload.Day = gps.date.day();
  payload.Month = gps.date.month();
  payload.Year = gps.date.year();
  vw_send((uint8_t *)&payload, sizeof(payload)); //Transmits the struct
  vw_wait_tx(); //waits for the TX to complete

transmitTimer = random(0, 86399);
  lcd.clear();
}

static void smartDelay(unsigned long ms)
{
  unsigned long start = millis();
  do
  {
    while (Serial.available())
      gps.encode(Serial.read());
  } while (millis() - start < ms);
}

void loop()
{

smartDelay (0); // get the gps data

if (millis() > SerialTimeout + 1500 ) { // detects if the Serial comms has failed. // if the position hasn't become valid in 1.5 seconds then display No serial.

displayNoSerial();

SerialTimeout = millis (); // reset the serial time out
  }
  secsPastMidnight =  gps.time.second() + (gps.time.minute() * 60) + (gps.time.hour() * 3600UL); // number of seconds past midnight
  secsToMidnight = 86399UL - secsPastMidnight ; // number of second to midnight.

if (transmitTimer >= secsPastMidnight) { // ensures the seconds to TX display is correct.
    timerPrint = transmitTimer - secsPastMidnight;
  }
  else {
    timerPrint = transmitTimer + secsToMidnight;
  }

if (secsPastMidnight == transmitTimer) { //if it's time to transmit, do it.
    transmitTime();
  }

if (digitalRead (A3) == LOW) { // Checks the "push to transmit" button, and transmits if it's low.
    transmitTime();
  }

if (gps.location.isUpdated() ) { // if there's new data, display it.
    displayData();
  }

}

/*
   Copyright (c) 2016 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 permiSerialion notice shall be included in
   all copies or substantial portions of the Software.

Any commercial use is prohibited without prior arrangement.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   FITNESerial 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.
*/

and the test receiver code...

/*
  GPS Master clock receiver
  (C) Andy Doswell 22nd July 2016
  License: The MIT License (See full license at the bottom of this file)

Schematic can be found at www.andydoz.blogspot.com/

#include <VirtualWire.h>
#include <VirtualWire_Config.h>

int TX_ID = 1;
int Hours;
int Mins;
int Secs;
int Day;
int Month;
int Year;
boolean Output;
char buffer[5];
int led = 13;

void setup() {
  pinMode(led, OUTPUT);
  //Comms set up
  Serial.begin(9600);
  // Virtualwire setup
  vw_set_tx_pin(10); // Even though it's not used, we'll define it so the default doesn't interfere with the LCD library.
  vw_set_rx_pin(9); // RX pin set to pin 9
  vw_setup(1200); //sets virtualwire for a tx rate of 300 bits per second, nice and slow!
  vw_rx_start();
}
void loop()
{
  typedef struct rxRemoteData //Defines the received data, this is the same as the TX struct
  {
    int TX_ID;
    int Hours;
    int Mins;
    int Secs;
    int Day;
    int Month;
    int Year;

};

struct rxRemoteData receivedData;
  uint8_t rcvdSize = sizeof(receivedData);

if (vw_get_message((uint8_t *)&receivedData, &rcvdSize))
  {
    if (receivedData.TX_ID == 1)     { //Only if the TX_ID=1 do we process the data.
      int TX_ID = receivedData.TX_ID;
      int Hours = receivedData.Hours;
      int Mins = receivedData.Mins;
      int Secs = receivedData.Secs;
      int Day =  receivedData.Day;
      int Month =  receivedData.Month;
      int Year =  receivedData.Year;
      digitalWrite(led, HIGH);

// writes the received data to the serial interface

Serial.print(itoa((Hours), buffer, 10));
      Serial.print(":");
      Serial.print(itoa((Mins), buffer, 10));
      Serial.print(":");
      Serial.print(itoa((Secs), buffer, 10));
      Serial.print(" ");
      Serial.print(itoa((Day), buffer, 10));
      Serial.print("/");
      Serial.print(itoa((Month), buffer, 10));
      Serial.print("/");
      Serial.println(itoa((Year), buffer, 10));
      digitalWrite(led, LOW);

}

The above copyright notice and this permiSerialion notice shall be included in
   all copies or substantial portions of the Software.

Any commercial use is prohibited without prior arrangement.

Now all that remains is to box it up, and create some clocks!

7 comments:

dancopy23 July 2017 at 01:23
I do not understand, are they two codes? I would like the code for the clock; Sorry and thank you
Kyle Fynn20 April 2018 at 23:43
Hi Andy, If i wanted to transmit the GPS longitude and latitude co-ordinates to the receiver every 1 second, how would i restructure the code?
speed up computer5 April 2021 at 11:25
nice blog.

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Friday, 22 July 2016

Arduino GPS master clock with 433/315 MHz transmitter

7 comments: