GPS Version 3

Here's an update to the code:

// GPS v3 module and LCD display
// display is limited to 16 x 2, so some data truncated
// Antony Watts 2014

/* GPS Pin connections
Module - Arduino
GND    -     GND
RX     -  Pin 11 TXPIN
TX     -  Pin 10 RXPIN
VCC    -    3.3V !!!!!
*/

// libraries
#include "SoftwareSerial.h"
#include "LiquidCrystal.h"

// GPS connections
#define RXPIN 10
#define TXPIN 11
#define BAUD 9600

// $GPRMC field positions in NMEA stream
#define RMCUTC 1
#define RMCLAT 3
#define RMCNS 4
#define RMCLON 5
#define RMCEW 6
#define RMCSOG 7
#define RMCCOG 8
#define RMCDATE 9

// LCD connections
#define RS 2
#define EN 3
#define D4 4
#define D5 5
#define D6 6
#define D7 7

// set up serial comms for GPS
SoftwareSerial gps(RXPIN, TXPIN); // serial comms to GPS UART

// Create LCD object
LiquidCrystal lcd(RS, EN, D4, D5, D6, D7);

void setup()
{
  gps.begin(BAUD); // start GPS serial
  lcd.begin(16, 2); // start LCD 16 col x 2 row
}

void loop()
{
  // main data buffers, NMEA read and field extract
  char gpsbuf[200];
  char ebuf[20];
  
  readgps(gpsbuf); // read each $GPxxx NMEAstrings+CRLF into gpsbuf
  
  // use $GPRMC string
  if(strncmp(gpsbuf, "$GPRMC", 6) == 0)
  { 
    extract(RMCUTC, gpsbuf, ebuf); // get utc
    lcdrpt(ebuf, 9, 0, "**:**"); // display lcd at col 9, row 0, in format hh:mm
      
    extract(RMCLAT, gpsbuf, ebuf); // get lat
    lcdrpt(ebuf, 0, 1, "** ****"); // display lcd at col 0 row 1, in format dd mmmm
    
    extract(RMCNS, gpsbuf, ebuf); // get N|S
    lcdrpt(ebuf, 7, 1, "* ");
    
    extract(RMCLON, gpsbuf, ebuf); // get lon
    lcdrpt(ebuf, 9, 1, "*** **");
    
    extract(RMCEW, gpsbuf, ebuf); // get E|W
    lcdrpt(ebuf, 15, 1, "* ");
    
//    extract(RMCSOG, gpsbuf, ebuf); // get SOG
    
//    extract(RMCCOG, gpsbuf, ebuf); // get COG
    
    extract(RMCDATE, gpsbuf, ebuf); // get date
    lcdrpt(ebuf, 0, 0, "**-**-**");
  }
}

// read GPxxx NMEA string into buffer
void readgps(char *buffer) 
{
  int bp;
  char c;
  
  bp = 0;
  do
  {
    c = gps.read();
    if(c == -1) continue; // gps sends -1 when idle
    buffer[bp++] = c;
  } while(c != '\n'); // ends with LF
  buffer[bp] = '\0'; // add '\0'
}

// extract string from field 0-10 from inbuf to outbuf
void extract(int field, char *inbuf, char *outbuf)
{
  int fcount; // field counter
  int ip; // inbuf pointer
  int op; // outbuf ptr

  fcount = 0;
  ip = 0;
  op = 0;
  
  while(fcount != field) // find field
  {
    while(inbuf[ip++] != ',');
    fcount++;
  }
  
  while(inbuf[ip] != ',') // copy inbuf to outbuf
  {
    outbuf[op++] = inbuf[ip++];
  }
  outbuf[op] = '\0'; // mark end of string
}

// display inbuf at col row in fmtbuf format
// display: * = use inbuf character, otherwise use fmtbuf character
int lcdrpt(char *inbuf, int col, int row, char *fmtbuf)
{
 int inp; // pointers to inbuf and format
 int fmtp;
 
 inp = 0; // start at buffers beginning
 fmtp = 0;
 
 lcd.setCursor(col, row);// start writing here
 
 while(fmtbuf[fmtp] != '\0') // continue until '\0' of format
 {
   if(fmtbuf[fmtp] == '*') // use inbuf character
   {
     lcd.write(inbuf[inp++]); // write inbuf char to lcd
   }
   else
   {
     lcd.write(fmtbuf[fmtp]); // format character
   }
   fmtp++;
 }
}

SDR Musings

Here's a thought... for a very integrated SDR TX/RX. The idea sprung from the bi-directional mixer in the "Minima" TX/RX design plus the IQ and audio parts of the Softrock Ensemble TX/RX design. This is the idea:



Sorry for the bad photo...

The 20MHz fixed oscillator is divided by 4 to give the 0deg and 90deg phase signal for the encoder/decoder. The RX & TX mixers are the well known SDR DSB generators with audio in and out. The "Minima" balanced mixer is bi -directional (!) and interfaces on both TX & RX with the antenna through a LPF.

My guess is that this would take

1 transistor for the oscillator,

a dual JK flip flop for the diviered,

two CMOS switches for encode/decode and

a couple of FETs for the balanced mixer.

Plus a quad op amp for the audio in/out.

Pretty simple eh? and NO tuning coils or caps.

The balanced mixer is fed with I & Q signals from the local VFO/divider chain . But this could be an AD9854 synthesiser module controlled by an Arduino. The AD9854 outputs both I & Q (0 & 90deg) signals at the fundamental frequency - avoiding the need for the /4 Johnson counter. Unfortunately no one seems to make an Arduino module for the chip.

Frequency generator AD9850

Thanks to various amateur radio enthusiasts for the code that makes this work.

I intend to expand it soon to include a tuning input (maybe push buttons, may be a knob...?) and a display of the frequency (that should be easy).

The module I used was just $3.5 on eBay!! And it is on sale from numerous suppliers in China - plus on in UK for £103!!! Clown.

Here's the setup



It is extremely easy to use the module, just four connections if in the serial communications mode set by pulsing FQ high.

This is the code

// DDS-9850 module programmer
 
#define W_CLK 8       // Pin 8  CLK
#define FQ_UD 9       // Pin 9  FQ
#define DATA 10       // Pin 10 DATA
#define RESET 11      // Pin 11 RST
 
#define pulseHigh(pin) {digitalWrite(pin, HIGH); digitalWrite(pin, LOW); }

void setup()
{
  pinMode(FQ_UD, OUTPUT);
  pinMode(W_CLK, OUTPUT);
  pinMode(DATA, OUTPUT);
  pinMode(RESET, OUTPUT);
   
  pulseHigh(RESET);
  pulseHigh(W_CLK);
  pulseHigh(FQ_UD);  // this pulse enables serial mode
}

void loop() 
{
  sendFrequency(14.23e6);  // freq MHz e6
  while(1);
}

 // transfers a byte, a bit at a time, LSB first via serial DATA line
void tfr_byte(byte data)
{
  for (int i=0; i<8; i++, data>>=1) 
  {
    digitalWrite(DATA, data & 0x01);
    pulseHigh(W_CLK);   //after each bit sent, CLK is pulsed high
  }
}

 // frequency calc from datasheet page 8 =  * /2^32
void sendFrequency(double frequency) 
{
  int32_t freq = frequency * 4294967295/125000000;  // note 125 MHz clock on 9850
  
  for (int b=0; b<4; b++, freq>>=8) 
  {
    tfr_byte(freq & 0xFF);
  }
  tfr_byte(0x000);   // Final control byte, all 0
  pulseHigh(FQ_UD);
}

I have so far only tested it by generating the 14.230MHz signal you can see it is programmed for and listening on an experimental SSTV receiver that I have nearly completed - more news soon.

GPS version 2

In the last post I showed my first attempt at using a GPS module and displaying the position, time and date.

I have since updated this to use a larger screen. Here are some pictures



This is the GPS module sitting on a breadboard shield on top of an Arduino Uno.



This is the display on the LCD.

To code the display I have used a library called u8glib.h available on GitHub. This is a quite complex library. It allows you to create an LCD object and defines a number of methods for acting on it.

There are a number of ways to define a "construct" (or object) but I have used this simple one for the display which is 128 x 64 with an ST7920 controller.

U8GLIB_ST7920_128X64_1X lcd(SCK, MOSI, SS);

The Arduino pins SCK is the SPI bus clock, MOSI is the data line and SS is the chip select. These are connected to the display LCD signals E, R/W and RS.

Methods

lcd.begin(); // reset display and put in default state
lcd.enableCursor(); // cursor visible
lcd,disableCursor(); // cursor not visible (default state)
lcd.setCursorPos(x, y); // cursor to x, y
lcd.setColorindex(col); // BW on = 1, off = 0
lcd.drawBitMap(x, y, cnt, h, *bitmap); // draw bit map of cnt bytes
                                       // width is cnt * 8
                                       // at x, y (top left) of height h
lcd.drawBox(x, y, w, h); // filled box at x, y. width w, height h
                         // fill set by color index
lcd.drawCircle(x, y, rad, opt); // x, y centre of circle radius rad, 
                                // opt is option to draw part of circle
                                // U8G_DRAW_UPPER_RIGHT, ...LEFT,
                                //  ... LOWER_LEFT, ... RIGHT, ...ALL
lcd.drawDisk(x, y, rad, opt); // as above but filled circle
lcd.drawFrame(x, y, w, h); // frame at x, y width w height h, color index
lcd.drawRFrame(x, y, w, h, r); // rounded frame, edges radius r
lcd.drawHLine(x, y, w); // draw horizontal line from x,y width w (pixels)
lcd.drawVLine(x, y, h); // draw vertical line from x, y height h (pixels)
lcd.drawLine(x1, y1, x2, y2,); // draw line from x1, y1 to x2, y2
drawTriangle(x1, y1, x2, y2, x3, y3); // filled triangle
lcd.drawPixel(x, y); // pixel at x, y
lcd.setFont(*font); // sets font - see table below
lcd.getStrWidth(*s); // returns string width in pixels in current font
lcd.drawStr(x, y, *s); // string at x, lower left of characters in setFont
                       // variations on this draw at 90, 180, 270 degrees
lcd.firstPage(); // starts a “picture loop”
lcd.nextPage(); // marks end of “picture loop”, returns 0 if finished

The display can use a wide range of fonts, the one I used is called "u8g_font_helvR08" or Helvetica Regular 8 point.

Code

#include "SoftwareSerial.h"
#include "U8glib.h"

// GPS comms 11 RX, 10 TX and LCD u8g object 6 SCK(E), 5 MOSI(RW), 4 SS(RS)
SoftwareSerial gps(10, 11);
U8GLIB_ST7920_128X64_1X u8g(6, 5, 4);

void setup()
{
    gps.begin(9600); // start GPS serial
}

void loop()
{
  char gpsbuf[200];
  char ebuf[9][20];
  
  readgps(gpsbuf); // read each $GPxxx NMEAstrings+CRLF into gpsbuf

    
  // use $GPRMC, 142759.00,A,5204.81158,N,00120.76633,W,0.107,,,090114,,,A*67
  // fields 1, 3, 4, 5, 6, 9
  if(strncmp(gpsbuf, "$GPRMC", 6) == 0)
  { 
    extract(1, gpsbuf, ebuf[1]); // get utc
    fmt(ebuf[1], "**:**:**"); // format utc
   
    extract(3, gpsbuf, ebuf[3]); // get lat
    fmt(ebuf[3], "** ****"); // format lat

    extract(4, gpsbuf, ebuf[4]); // get N|S
    fmt(ebuf[4], "*"); // format N|S

    extract(5, gpsbuf, ebuf[5]); // get lon
    fmt(ebuf[5], "*** ****"); // format lon

    extract(6, gpsbuf, ebuf[6]); // get E|W
    fmt(ebuf[6], "*"); // format E|W

    extract(9, gpsbuf, ebuf[9]); // get date
    fmt(ebuf[9], "**-**-**"); // format date
    
    u8g.firstPage();
    do
    {
      u8g.setFont(u8g_font_helvR08);
      
      u8g.drawStr(2, 8, "Latitude");            
      u8g.drawStr(66, 8, "Longitude");
      
      u8g.drawStr(2, 19, ebuf[3]); // Lat
      u8g.drawStr(40, 19, ebuf[4]);
      u8g.drawStr(66, 19, ebuf[5]); // Lon
      u8g.drawStr(110, 19, ebuf[6]);
      
      u8g.drawStr(2, 40, "Time");
      u8g.drawStr(66, 40, "Date");
      
      u8g.drawStr(2, 51, ebuf[1]); // UTC
      u8g.drawStr(66, 51, ebuf[9]); // Date   
    } while(u8g.nextPage());    
  }
}

// read GPxxx NMEA string into buffer
void readgps(char *buffer) 
{
  int bp;
  char c;
  
  bp = 0;
  do
  {
    c = gps.read();
    if(c == -1) continue; // gps sends -1 when idle
    buffer[bp++] = c;
  } while(c != '\n'); // ends with LF
  buffer[bp] = '\0'; // add '\0'
}

// extract string from field 0-10 from inbuf to outbuf
void extract(int field, char *inbuf, char *outbuf)
{
  int fcount; // field counter
  int ip; // inbuf pointer
  int op; // outbuf ptr

  fcount = 0;
  ip = 0;
  op = 0;
  
  while(fcount != field) // find field
  {
    while(inbuf[ip++] != ',');
    fcount++;
  }
  
  while(inbuf[ip] != ',') // copy inbuf to outbuf
  {
    outbuf[op++] = inbuf[ip++];
  }
  outbuf[op] = '\0'; // mark end of string
}

// formats buffer with fmtstr, result back in buffer
void fmt(char *buffer, char *fmtstr)
{
  char tmp[20];
  int bp, fp, tp; // buffer, fmtstr & tmp pointers
  
  bp = 0;
  fp = 0;
  tp = 0;
  
  strcpy(tmp, buffer);
  while(fmtstr[fp] != '\0')
  {
    if(fmtstr[fp] == '*')
    {
      buffer[bp] = tmp[tp++];
    }
    else 
    {
      buffer[bp] = fmtstr[fp];
    }
    fp++;
    bp++;
  }
  buffer[bp] = '\0';
}

GPS

Now here's a more complicated project. A GPS receiver with display of date, time, latitude and longitude. The decoded information from the receiver is:



The SOG & COG are not meaningful as the receiver is not moving...

The GPS module, wiring and LCD display look like this:




The display is limited to 16 characters so some information is truncated (no time in seconds for example, no decimal minutes of longitude). Wiring diagram:




The GPS receiver outputs various strings of information according to the NMEA specification. Noteable are these:



The string I am using is the $GPRMC one, which reports the data I need.

Software code

// GPS v3 module and LCD display
// display is limited to 16 x 2, so some data truncated
// Antony Watts 2014

/* GPS Pin connections
Module - Arduino
GND    -     GND
RX     -  Pin 11 TXPIN
TX     -  Pin 10 RXPIN
VCC    -    3.3V !!!!!
*/

// libraries
#include 
#include 

// GPS connections
#define RXPIN 10
#define TXPIN 11
#define BAUD 9600

// $GPRMC field positions in NMEA stream
#define RMCUTC 1
#define RMCLAT 3
#define RMCNS 4
#define RMCLON 5
#define RMCEW 6
#define RMCSOG 7
#define RMCCOG 8
#define RMCDATE 9

// LCD connections
#define RS 2
#define EN 3
#define D4 4
#define D5 5
#define D6 6
#define D7 7

// set up serial comms for GPS
SoftwareSerial gps(RXPIN, TXPIN); // serial comms to GPS UART

// Create LCD object
LiquidCrystal lcd(RS, EN, D4, D5, D6, D7);

void setup()
{
  gps.begin(BAUD); // start GPS serial
  lcd.begin(16, 2); // start LCD 16 col x 2 row
}

void loop()
{
  // main data buffers, NMEA read and field extract
  char gpsbuf[200];
  char ebuf[20];
  
  readgps(gpsbuf); // read each $GPxxx NMEAstrings+CRLF into gpsbuf
  
  if(strncmp(gpsbuf, "$GPRMC", 6) == 0)// use $GPRMC string
  { 
    extract(RMCUTC, gpsbuf, ebuf); // get utc
    lcdrpt(ebuf, 9, 0, "**:**"); // display lcd at col 9, row 0
      
    extract(RMCLAT, gpsbuf, ebuf); // get lat
    lcdrpt(ebuf, 0, 1, "** ****");
    
    extract(RMCNS, gpsbuf, ebuf); // get N|S
    lcdrpt(ebuf, 7, 1, "* ");
    
    extract(RMCLON, gpsbuf, ebuf); // get lon
    lcdrpt(ebuf, 9, 1, "*** **");
    
    extract(RMCEW, gpsbuf, ebuf); // get E|W
    lcdrpt(ebuf, 15, 1, "* ");
    
//    extract(RMCSOG, gpsbuf, ebuf); // get SOG
    
//    extract(RMCCOG, gpsbuf, ebuf); // get COG
    
    extract(RMCDATE, gpsbuf, ebuf); // get date
    lcdrpt(ebuf, 0, 0, "**-**-**");
  }
}

// read GPxxx NMEA string into buffer
void readgps(char *buffer) 
{
  int bp;
  char c;
  
  bp = 0;
  do
  {
    c = gps.read();
    if(c == -1) continue; // gps sends -1 when idle
    buffer[bp++] = c;
  } while(c != '\n'); // ends with LF
  buffer[bp] = '\0'; // add '\0'
}

// extract string from field 0-10 from inbuf to outbuf
void extract(int field, char *inbuf, char *outbuf)
{
  int fcount; // field counter
  int ip; // inbuf pointer
  int op; // outbug ptr

  fcount = 0;
  ip = 0;
  op = 0;
  
  while(fcount != field) // find field
  {
    while(inbuf[ip++] != ',');
    fcount++;
  }
  
  while(inbuf[ip] != ',') // copy inbuf to outbuf
  {
    outbuf[op++] = inbuf[ip++];
  }
  outbuf[op] = '\0'; // mark end of string
}

// display inbuf at col row in fmtbuf format
// display: * = use inbuf character, otherwise use fmtbuf character
int lcdrpt(char *inbuf, int col, int row, char *fmtbuf)
{
 int inp; // pointers to inbuf and format
 int fmtp;
 
 inp = 0; // start at buffers beginning
 fmtp = 0;
 
 lcd.setCursor(col, row);// start writing here
 
 while(fmtbuf[fmtp] != '\0') // continue until '\0' of format
 {
   if(fmtbuf[fmtp] == '*') // use inbuf character
   {
     lcd.write(inbuf[inp++]); // write inbuf char to lcd
   }
   else
   {
     lcd.write(fmtbuf[fmtp]); // format character
   }
   fmtp++;
 }
}