Car HUD - Windscreen Display for Speed+Compass+Alt.

Drive without distracting your sight, take care of speed limits taking under control your car speed on windscreen! (2nd version available)

Dec 10, 2020

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gps

tracking

cars

Components and supplies

Arduino Nano R3

Project description

Code

Car-HUD Arduino sketch

arduino

1/*
2  This sketch acts as car windscreen HUD (head up display), by Marco   Zonca, 10/2020
3  Arduino Nano as CPU, GPS BT-220 nmea every 1 sec, 3 x buttons,   3 x seven segment displays common cathode,
4  3 x 14511 BCD latch decoder, MPU   EEPROM memory (1 byte) and many resistors;
5
6  WARNING:
7  =======
8  Before   updating software let disconnect RX pin on Arduino (TX from GPS) by the way of the   JUMPER
9*/
10
11#include <Wire.h>
12#include <EEPROM.h>
13
14String inputString   = "";
15String nm_time = "00:00:00";
16String nm_validity = "V";
17String   nm_latitude = "dd°mm.mmmm'N";
18String nm_longitude = "ddd°mm.mmmm'E";
19String   nm_knots = "0.0kn";
20float nmf_knots = 0.0;
21float nmf_kmh = 0.0;
22int nmi_kmh   = 0;
23String nm_truecourse = "360";
24float nmf_truecourse = 360;
25String   nm_date = "dd/mm/yyyy";
26int nmi_truecourse = 0;
27byte kCent = 0;
28byte   kDeci = 0;
29byte kUnit = 0;
30byte tCent = 0;
31byte tDeci = 0;
32byte tUnit   = 0;
33byte brightness = 120;
34byte latch_off = HIGH;
35byte latch_on = LOW;
36int   n=0;
37unsigned long lastmemcheck = 0;
38unsigned long memcheck = 60000;  // check   to save "brightness" value in EEPROM every 60 seconds
39
40bool stringComplete   = false;
41bool isKMH=true;
42bool ret = false;
43
44const int disp001 = 2;   // units display latch
45const int disp010 = 8;  // tens display latch
46const   int disp100 = 12;  // undreds display latch
47
48const int disp001dim = 9;  //   units display dimmer/off pin
49const int disp010dim = 10;  // tens display dimmer/off   pin
50const int disp100dim = 11;  // undreds display dimmer/off pin
51
52const   int button_kt = 14;  // kmh/truecourse button
53const int button_more = 15;  //   brightness + button
54const int button_less = 16;  // brightness - button
55
56const   int degreesLED = 3;  // degrees LED
57
58const int bit_3 = 7;  // bit 3
59const   int bit_2 = 6;  // bit 2
60const int bit_1 = 5;  // bit 1
61const int bit_0 =   4;  // bit 0
62
63const int dly = 10;  // delay latch m/sec
64const byte off   = 0;  // the same as brightness=0
65const int addr = 0; // EEPROM address for brightness   value
66
67const byte numbers[10] [4] = {{0,0,0,0},{1,0,0,0},{0,1,0,0},{1,1,0,0},{0,0,1,0},
68                               {1,0,1,0},{0,1,1,0},{1,1,1,0},{0,0,0,1},{1,0,0,1}};   // bits 0,1,2,3
69
70void setup() {
71  Serial.begin(9600);
72  Wire.begin();
73   inputString.reserve(200);
74  brightness = EEPROM.read(addr);
75  if (brightness   > 250 || brightness < 10) { brightness=120; }  // avoid crazy values from 1st EEPROM   read
76  pinMode(disp001, OUTPUT);
77  pinMode(disp010, OUTPUT);
78  pinMode(disp100,   OUTPUT);
79  pinMode(degreesLED, OUTPUT);
80  pinMode(button_kt, INPUT_PULLUP);
81   pinMode(button_less, INPUT_PULLUP);
82  pinMode(button_more, INPUT_PULLUP);
83   pinMode(bit_3, OUTPUT);
84  pinMode(bit_2, OUTPUT);
85  pinMode(bit_1, OUTPUT);
86   pinMode(bit_0, OUTPUT);  
87  
88  analogWrite(disp001dim, off);  // off and   zero displays
89  analogWrite(disp010dim, off);
90  analogWrite(disp100dim, off);
91   analogWrite(degreesLED, off);
92  
93  setBusNr(0);
94  digitalWrite(disp001,   latch_on);
95  digitalWrite(disp010, latch_on);
96  digitalWrite(disp100, latch_on);
97   delay(dly);
98  digitalWrite(disp001, latch_off);
99  digitalWrite(disp010,   latch_off);
100  digitalWrite(disp100, latch_off);
101
102  analogWrite(disp001dim,   brightness);  // on display
103  analogWrite(disp010dim, brightness);
104  analogWrite(disp100dim,   brightness);
105}  // setup()
106
107void loop() {
108  // GPS NMEA ------------------
109   if (stringComplete == true) {  // received nmea sentence by serial port RX
110     ret = nmeaExtractData();
111    inputString = "";
112    stringComplete =   false;
113    if (ret == true) {
114      kCent=nmi_kmh/100;
115      n=nmi_kmh-(kCent*100);
116       kDeci=n/10;
117      n=nmi_kmh-(kCent*100)-(kDeci*10);
118      kUnit=n;
119       tCent=nmi_truecourse/100;
120      n=nmi_truecourse-(tCent*100);
121      tDeci=n/10;
122       n=nmi_truecourse-(tCent*100)-(tDeci*10);
123      tUnit=n;
124      display();
125     }
126  }
127  if (millis() > (lastmemcheck+memcheck)) {  // put in memory brightness   value (if modified)
128    EEPROM.update(addr,brightness);
129    lastmemcheck=millis();
130   }
131  checkButtons();
132}
133
134void display() {
135  if (isKMH == true) {   // speed in km/h (isKMH=true)
136    analogWrite(degreesLED, off);
137    setBusNr(kUnit);
138     digitalWrite(disp001, latch_on);
139    delay(dly);
140    digitalWrite(disp001,   latch_off);
141    if (kDeci > 0 || kCent > 0) {  // set tens off if tens=0 (and   also undreds=0)
142      setBusNr(kDeci);
143      digitalWrite(disp010, latch_on);
144       delay(dly);
145      digitalWrite(disp010, latch_off);
146      analogWrite(disp010dim,   brightness);
147    } else {
148      analogWrite(disp010dim, off);
149    }
150     if (kCent > 0) {  // set undreds off if=0
151      setBusNr(kCent);
152      digitalWrite(disp100,   latch_on);
153      delay(dly);
154      digitalWrite(disp100, latch_off);
155      analogWrite(disp100dim,   brightness);
156    } else {
157      analogWrite(disp100dim, off);
158    }
159   } else {  // true bearing in degrees (isKMH=false) 
160    analogWrite(degreesLED,   brightness);
161    setBusNr(tUnit);
162    digitalWrite(disp001, latch_on);
163     delay(dly);
164    digitalWrite(disp001, latch_off);
165    if (tDeci > 0 ||   tCent > 0) {  // set tens off if tens=0 (and also undreds=0)
166      setBusNr(tDeci);
167       digitalWrite(disp010, latch_on);
168      delay(dly);
169      digitalWrite(disp010,   latch_off);
170      analogWrite(disp010dim, brightness);
171    } else {
172      analogWrite(disp010dim,   off);
173    }
174    if (tCent > 0) {  // set undreds off if=0
175      setBusNr(tCent);
176       digitalWrite(disp100, latch_on);
177      delay(dly);
178      digitalWrite(disp100,   latch_off);
179      analogWrite(disp100dim, brightness);
180    } else { 
181      analogWrite(disp100dim,   off);
182    }
183  }
184}  // display()
185
186void checkButtons(){
187  if (digitalRead(button_kt)   == LOW) {
188    if (isKMH == true) {
189      isKMH=false;
190    } else {
191       isKMH=true;
192    }
193    delay(250);
194  }
195  if (digitalRead(button_more)   == LOW) {
196    if (brightness <= 240) {
197      brightness=brightness+10;
198     }
199    analogWrite(disp001dim, brightness);
200    analogWrite(disp010dim,   brightness);
201    analogWrite(disp100dim, brightness);
202    delay(100);
203   }
204  if (digitalRead(button_less) == LOW) {
205    if (brightness >= 20) {
206       brightness=brightness-10;
207    }
208    analogWrite(disp001dim, brightness);
209     analogWrite(disp010dim, brightness);
210    analogWrite(disp100dim, brightness);
211     delay(100);
212  }
213}  // checkButtons()
214
215void setBusNr(int number)   {  // sets 4 bits bus
216  for (byte b=0; b<=3; b++) {
217    if (numbers[number][b]==0)   {
218      if (b==0) {digitalWrite(bit_0, LOW);}
219      if (b==1) {digitalWrite(bit_1,   LOW);}
220      if (b==2) {digitalWrite(bit_2, LOW);}
221      if (b==3) {digitalWrite(bit_3,   LOW);}
222    } else {
223      if (b==0) {digitalWrite(bit_0, HIGH);}
224      if   (b==1) {digitalWrite(bit_1, HIGH);}
225      if (b==2) {digitalWrite(bit_2, HIGH);}
226       if (b==3) {digitalWrite(bit_3, HIGH);}
227    }
228  }
229}  // setBusNr()
230
231//   extract data from nmea inputString
232bool nmeaExtractData() {
233  int d=0;
234   int s=0;
235  int y=0;
236  int z=0;
237  float t=0;
238  bool ret = false;  //true   if nmea sentence = $GNRMC and valid CHKSUM
239  if ((inputString.substring(0,6)   == "$GNRMC") && (inputString.substring(inputString.length()-4,inputString.length()-2)   == nmea0183_checksum(inputString))) {
240    y=0;
241    for (s = 1; s < 11; s ++)   { 
242      y=inputString.indexOf(",",y);
243      switch (s) {
244      case   1: //-----------------------time
245        z=inputString.indexOf(",",y+1);
246         if (z>(y+1)) {
247          nm_time=inputString.substring(y+1,y+2+1)+":"+inputString.substring(y+1+2,y+4+1)+":"+inputString.substring(y+1+4,y+6+1);
248         }
249        y=z;
250        break;
251      case 2: //-----------------------validity
252         z=inputString.indexOf(",",y+1);
253        if (z>(y+1)) {
254          nm_validity=inputString.substring(y+1,y+1+1);
255         }
256        y=z;
257        break;
258      case 3: //-----------------------latitude
259         z=inputString.indexOf(",",y+1);
260        if (z>(y+1)) {
261          nm_latitude=inputString.substring(y+1,y+2+1)+"°"+inputString.substring(y+1+2,y+10+1)+"'";
262         }
263        y=z;
264        break;
265      case 4: //-----------------------north/south
266         z=inputString.indexOf(",",y+1);
267        if (z>(y+1)) {
268          nm_latitude=nm_latitude   + inputString.substring(y+1,y+1+1);
269        }
270        y=z;
271        break;
272       case 5: //-----------------------longitude
273        z=inputString.indexOf(",",y+1);
274         if (z>(y+1)) {
275          nm_longitude=inputString.substring(y+1,y+3+1)+"°"+inputString.substring(y+1+3,y+11+1)+"'";
276         }
277        y=z;
278        break;
279      case 6: //-----------------------east/west
280         z=inputString.indexOf(",",y+1);
281        if (z>(y+1)) {
282          nm_longitude=nm_longitude   + inputString.substring(y+1,y+1+1);
283        }
284        y=z;
285        break;
286       case 7:  //-----------------------speed knots
287        z=inputString.indexOf(",",y+1);
288         if (z>(y+1)) {
289          nmf_knots=inputString.substring(y+1,z).toFloat();
290           t=roundOneDec(nmf_knots);
291          nm_knots=String(t,1)+"kn";
292           nmf_kmh=roundTwoDec(nmf_knots * 1.852);
293          nmi_kmh=roundZeroDec(nmf_knots   * 1.852);
294        }
295        y=z;
296        break;
297      case 8: //-----------------------true   course
298        z=inputString.indexOf(",",y+1);
299        if (z>(y+1)) {
300           nmf_truecourse=inputString.substring(y+1,z).toFloat();
301          t=roundZeroDec(nmf_truecourse);
302           nmi_truecourse=t;
303          d=t;
304          nm_truecourse=d;
305         }
306        y=z;
307        break;
308      case 9: //-----------------------date
309         z=inputString.indexOf(",",y+1);
310        if (z>(y+1)) {
311          nm_date=inputString.substring(y+1,y+2+1)+"/"+inputString.substring(y+1+2,y+4+1)+"/20"+inputString.substring(y+1+4,y+6+1);
312         }
313        y=z;
314        break;
315      case 10:
316        // statements   n.u.
317        break;
318      default:
319        // statements n.u.
320        break;
321       }
322    }
323    ret=true;
324  }
325  return ret;
326}  // nmeaExtractData()
327
328/*
329   SerialEvent occurs whenever a new data comes in the hardware serial RX. This
330   routine is run between each time loop() runs, so using delay inside loop can
331   delay response. Multiple bytes of data may be available.
332*/
333void serialEvent()   {
334  while (Serial.available()) {
335    char inChar = (char)Serial.read();
336     inputString += inChar;
337    // if the incoming character is a newline, set   a flag so the main loop can
338    // do something about it
339    if (inChar ==   '\
340') {
341      stringComplete = true;
342    }
343  }
344}  // serialEvent()
345
346//calculate   checksum of nmea sentence
347String nmea0183_checksum(String nmea_data) {
348    int   crc = 0;
349    String chSumString = "";
350    int i;
351    // ignore the first   $ sign, checksum in sentence
352    for (i = 1; i < (nmea_data.length()-5); i ++)   { // remove the - 5 if no "*" + cksum + cr + lf are present
353        crc ^=   nmea_data[i];
354    }
355    chSumString = String(crc,HEX);
356    if (chSumString.length()==1)   {
357      chSumString="0"+chSumString.substring(0,1);
358    }
359    chSumString.toUpperCase();
360     return chSumString;
361}  // nmea0183_checksum(String nmea_data)
362
363// round   zero decimals
364float roundZeroDec(float f) {
365  float y, d;
366  y = f*1;
367   d = y - (int)y;
368  y = (float)(int)(f*1)/1;
369  if (d >= 0.5) {
370    y +=   1;
371   } else {
372    if (d < -0.5) {
373    y -= 1;
374  }
375  }
376  return   y;
377}
378
379// round one decimal
380float roundOneDec(float f) {
381  float y,   d;
382  y = f*10;
383  d = y - (int)y;
384  y = (float)(int)(f*10)/10;
385  if (d   >= 0.5) {
386    y += 0.1;
387   } else {
388    if (d < -0.5) {
389    y -= 0.1;
390   }
391  }
392  return y;
393}
394
395// round two decimals
396float roundTwoDec(float   f) {
397  float y, d;
398  y = f*100;
399  d = y - (int)y;
400  y = (float)(int)(f*100)/100;
401   if (d >= 0.5) {
402    y += 0.01;
403   } else {
404    if (d < -0.5) {
405    y   -= 0.01;
406  }
407  }
408  return y;
409}
410

/*
  This sketch acts as car windscreen HUD (head up display), by Marco   Zonca, 10/2020
  Arduino Nano as CPU, GPS BT-220 nmea every 1 sec, 3 x buttons,   3 x seven segment displays common cathode,
  3 x 14511 BCD latch decoder, MPU   EEPROM memory (1 byte) and many resistors;

  WARNING:
  =======
  Before   updating software let disconnect RX pin on Arduino (TX from GPS) by the way of the   JUMPER
*/

#include <Wire.h>
#include <EEPROM.h>

String inputString   = "";
String nm_time = "00:00:00";
String nm_validity = "V";
String   nm_latitude = "dd°mm.mmmm'N";
String nm_longitude = "ddd°mm.mmmm'E";
String   nm_knots = "0.0kn";
float nmf_knots = 0.0;
float nmf_kmh = 0.0;
int nmi_kmh   = 0;
String nm_truecourse = "360";
float nmf_truecourse = 360;
String   nm_date = "dd/mm/yyyy";
int nmi_truecourse = 0;
byte kCent = 0;
byte   kDeci = 0;
byte kUnit = 0;
byte tCent = 0;
byte tDeci = 0;
byte tUnit   = 0;
byte brightness = 120;
byte latch_off = HIGH;
byte latch_on = LOW;
int   n=0;
unsigned long lastmemcheck = 0;
unsigned long memcheck = 60000;  // check   to save "brightness" value in EEPROM every 60 seconds

bool stringComplete   = false;
bool isKMH=true;
bool ret = false;

const int disp001 = 2;   // units display latch
const int disp010 = 8;  // tens display latch
const   int disp100 = 12;  // undreds display latch

const int disp001dim = 9;  //   units display dimmer/off pin
const int disp010dim = 10;  // tens display dimmer/off   pin
const int disp100dim = 11;  // undreds display dimmer/off pin

const   int button_kt = 14;  // kmh/truecourse button
const int button_more = 15;  //   brightness + button
const int button_less = 16;  // brightness - button

const   int degreesLED = 3;  // degrees LED

const int bit_3 = 7;  // bit 3
const   int bit_2 = 6;  // bit 2
const int bit_1 = 5;  // bit 1
const int bit_0 =   4;  // bit 0

const int dly = 10;  // delay latch m/sec
const byte off   = 0;  // the same as brightness=0
const int addr = 0; // EEPROM address for brightness   value

const byte numbers[10] [4] = {{0,0,0,0},{1,0,0,0},{0,1,0,0},{1,1,0,0},{0,0,1,0},
                               {1,0,1,0},{0,1,1,0},{1,1,1,0},{0,0,0,1},{1,0,0,1}};   // bits 0,1,2,3

void setup() {
  Serial.begin(9600);
  Wire.begin();
   inputString.reserve(200);
  brightness = EEPROM.read(addr);
  if (brightness   > 250 || brightness < 10) { brightness=120; }  // avoid crazy values from 1st EEPROM   read
  pinMode(disp001, OUTPUT);
  pinMode(disp010, OUTPUT);
  pinMode(disp100,   OUTPUT);
  pinMode(degreesLED, OUTPUT);
  pinMode(button_kt, INPUT_PULLUP);
   pinMode(button_less, INPUT_PULLUP);
  pinMode(button_more, INPUT_PULLUP);
   pinMode(bit_3, OUTPUT);
  pinMode(bit_2, OUTPUT);
  pinMode(bit_1, OUTPUT);
   pinMode(bit_0, OUTPUT);  
  
  analogWrite(disp001dim, off);  // off and   zero displays
  analogWrite(disp010dim, off);
  analogWrite(disp100dim, off);
   analogWrite(degreesLED, off);
  
  setBusNr(0);
  digitalWrite(disp001,   latch_on);
  digitalWrite(disp010, latch_on);
  digitalWrite(disp100, latch_on);
   delay(dly);
  digitalWrite(disp001, latch_off);
  digitalWrite(disp010,   latch_off);
  digitalWrite(disp100, latch_off);

  analogWrite(disp001dim,   brightness);  // on display
  analogWrite(disp010dim, brightness);
  analogWrite(disp100dim,   brightness);
}  // setup()

void loop() {
  // GPS NMEA ------------------
   if (stringComplete == true) {  // received nmea sentence by serial port RX
     ret = nmeaExtractData();
    inputString = "";
    stringComplete =   false;
    if (ret == true) {
      kCent=nmi_kmh/100;
      n=nmi_kmh-(kCent*100);
       kDeci=n/10;
      n=nmi_kmh-(kCent*100)-(kDeci*10);
      kUnit=n;
       tCent=nmi_truecourse/100;
      n=nmi_truecourse-(tCent*100);
      tDeci=n/10;
       n=nmi_truecourse-(tCent*100)-(tDeci*10);
      tUnit=n;
      display();
     }
  }
  if (millis() > (lastmemcheck+memcheck)) {  // put in memory brightness   value (if modified)
    EEPROM.update(addr,brightness);
    lastmemcheck=millis();
   }
  checkButtons();
}

void display() {
  if (isKMH == true) {   // speed in km/h (isKMH=true)
    analogWrite(degreesLED, off);
    setBusNr(kUnit);
     digitalWrite(disp001, latch_on);
    delay(dly);
    digitalWrite(disp001,   latch_off);
    if (kDeci > 0 || kCent > 0) {  // set tens off if tens=0 (and   also undreds=0)
      setBusNr(kDeci);
      digitalWrite(disp010, latch_on);
       delay(dly);
      digitalWrite(disp010, latch_off);
      analogWrite(disp010dim,   brightness);
    } else {
      analogWrite(disp010dim, off);
    }
     if (kCent > 0) {  // set undreds off if=0
      setBusNr(kCent);
      digitalWrite(disp100,   latch_on);
      delay(dly);
      digitalWrite(disp100, latch_off);
      analogWrite(disp100dim,   brightness);
    } else {
      analogWrite(disp100dim, off);
    }
   } else {  // true bearing in degrees (isKMH=false) 
    analogWrite(degreesLED,   brightness);
    setBusNr(tUnit);
    digitalWrite(disp001, latch_on);
     delay(dly);
    digitalWrite(disp001, latch_off);
    if (tDeci > 0 ||   tCent > 0) {  // set tens off if tens=0 (and also undreds=0)
      setBusNr(tDeci);
       digitalWrite(disp010, latch_on);
      delay(dly);
      digitalWrite(disp010,   latch_off);
      analogWrite(disp010dim, brightness);
    } else {
      analogWrite(disp010dim,   off);
    }
    if (tCent > 0) {  // set undreds off if=0
      setBusNr(tCent);
       digitalWrite(disp100, latch_on);
      delay(dly);
      digitalWrite(disp100,   latch_off);
      analogWrite(disp100dim, brightness);
    } else { 
      analogWrite(disp100dim,   off);
    }
  }
}  // display()

void checkButtons(){
  if (digitalRead(button_kt)   == LOW) {
    if (isKMH == true) {
      isKMH=false;
    } else {
       isKMH=true;
    }
    delay(250);
  }
  if (digitalRead(button_more)   == LOW) {
    if (brightness <= 240) {
      brightness=brightness+10;
     }
    analogWrite(disp001dim, brightness);
    analogWrite(disp010dim,   brightness);
    analogWrite(disp100dim, brightness);
    delay(100);
   }
  if (digitalRead(button_less) == LOW) {
    if (brightness >= 20) {
       brightness=brightness-10;
    }
    analogWrite(disp001dim, brightness);
     analogWrite(disp010dim, brightness);
    analogWrite(disp100dim, brightness);
     delay(100);
  }
}  // checkButtons()

void setBusNr(int number)   {  // sets 4 bits bus
  for (byte b=0; b<=3; b++) {
    if (numbers[number][b]==0)   {
      if (b==0) {digitalWrite(bit_0, LOW);}
      if (b==1) {digitalWrite(bit_1,   LOW);}
      if (b==2) {digitalWrite(bit_2, LOW);}
      if (b==3) {digitalWrite(bit_3,   LOW);}
    } else {
      if (b==0) {digitalWrite(bit_0, HIGH);}
      if   (b==1) {digitalWrite(bit_1, HIGH);}
      if (b==2) {digitalWrite(bit_2, HIGH);}
       if (b==3) {digitalWrite(bit_3, HIGH);}
    }
  }
}  // setBusNr()

//   extract data from nmea inputString
bool nmeaExtractData() {
  int d=0;
   int s=0;
  int y=0;
  int z=0;
  float t=0;
  bool ret = false;  //true   if nmea sentence = $GNRMC and valid CHKSUM
  if ((inputString.substring(0,6)   == "$GNRMC") && (inputString.substring(inputString.length()-4,inputString.length()-2)   == nmea0183_checksum(inputString))) {
    y=0;
    for (s = 1; s < 11; s ++)   { 
      y=inputString.indexOf(",",y);
      switch (s) {
      case   1: //-----------------------time
        z=inputString.indexOf(",",y+1);
         if (z>(y+1)) {
          nm_time=inputString.substring(y+1,y+2+1)+":"+inputString.substring(y+1+2,y+4+1)+":"+inputString.substring(y+1+4,y+6+1);
         }
        y=z;
        break;
      case 2: //-----------------------validity
         z=inputString.indexOf(",",y+1);
        if (z>(y+1)) {
          nm_validity=inputString.substring(y+1,y+1+1);
         }
        y=z;
        break;
      case 3: //-----------------------latitude
         z=inputString.indexOf(",",y+1);
        if (z>(y+1)) {
          nm_latitude=inputString.substring(y+1,y+2+1)+"°"+inputString.substring(y+1+2,y+10+1)+"'";
         }
        y=z;
        break;
      case 4: //-----------------------north/south
         z=inputString.indexOf(",",y+1);
        if (z>(y+1)) {
          nm_latitude=nm_latitude   + inputString.substring(y+1,y+1+1);
        }
        y=z;
        break;
       case 5: //-----------------------longitude
        z=inputString.indexOf(",",y+1);
         if (z>(y+1)) {
          nm_longitude=inputString.substring(y+1,y+3+1)+"°"+inputString.substring(y+1+3,y+11+1)+"'";
         }
        y=z;
        break;
      case 6: //-----------------------east/west
         z=inputString.indexOf(",",y+1);
        if (z>(y+1)) {
          nm_longitude=nm_longitude   + inputString.substring(y+1,y+1+1);
        }
        y=z;
        break;
       case 7:  //-----------------------speed knots
        z=inputString.indexOf(",",y+1);
         if (z>(y+1)) {
          nmf_knots=inputString.substring(y+1,z).toFloat();
           t=roundOneDec(nmf_knots);
          nm_knots=String(t,1)+"kn";
           nmf_kmh=roundTwoDec(nmf_knots * 1.852);
          nmi_kmh=roundZeroDec(nmf_knots   * 1.852);
        }
        y=z;
        break;
      case 8: //-----------------------true   course
        z=inputString.indexOf(",",y+1);
        if (z>(y+1)) {
           nmf_truecourse=inputString.substring(y+1,z).toFloat();
          t=roundZeroDec(nmf_truecourse);
           nmi_truecourse=t;
          d=t;
          nm_truecourse=d;
         }
        y=z;
        break;
      case 9: //-----------------------date
         z=inputString.indexOf(",",y+1);
        if (z>(y+1)) {
          nm_date=inputString.substring(y+1,y+2+1)+"/"+inputString.substring(y+1+2,y+4+1)+"/20"+inputString.substring(y+1+4,y+6+1);
         }
        y=z;
        break;
      case 10:
        // statements   n.u.
        break;
      default:
        // statements n.u.
        break;
       }
    }
    ret=true;
  }
  return ret;
}  // nmeaExtractData()

/*
   SerialEvent occurs whenever a new data comes in the hardware serial RX. This
   routine is run between each time loop() runs, so using delay inside loop can
   delay response. Multiple bytes of data may be available.
*/
void serialEvent()   {
  while (Serial.available()) {
    char inChar = (char)Serial.read();
     inputString += inChar;
    // if the incoming character is a newline, set   a flag so the main loop can
    // do something about it
    if (inChar ==   '\
') {
      stringComplete = true;
    }
  }
}  // serialEvent()

//calculate   checksum of nmea sentence
String nmea0183_checksum(String nmea_data) {
    int   crc = 0;
    String chSumString = "";
    int i;
    // ignore the first   $ sign, checksum in sentence
    for (i = 1; i < (nmea_data.length()-5); i ++)   { // remove the - 5 if no "*" + cksum + cr + lf are present
        crc ^=   nmea_data[i];
    }
    chSumString = String(crc,HEX);
    if (chSumString.length()==1)   {
      chSumString="0"+chSumString.substring(0,1);
    }
    chSumString.toUpperCase();
     return chSumString;
}  // nmea0183_checksum(String nmea_data)

// round   zero decimals
float roundZeroDec(float f) {
  float y, d;
  y = f*1;
   d = y - (int)y;
  y = (float)(int)(f*1)/1;
  if (d >= 0.5) {
    y +=   1;
   } else {
    if (d < -0.5) {
    y -= 1;
  }
  }
  return   y;
}

// round one decimal
float roundOneDec(float f) {
  float y,   d;
  y = f*10;
  d = y - (int)y;
  y = (float)(int)(f*10)/10;
  if (d   >= 0.5) {
    y += 0.1;
   } else {
    if (d < -0.5) {
    y -= 0.1;
   }
  }
  return y;
}

// round two decimals
float roundTwoDec(float   f) {
  float y, d;
  y = f*100;
  d = y - (int)y;
  y = (float)(int)(f*100)/100;
   if (d >= 0.5) {
    y += 0.01;
   } else {
    if (d < -0.5) {
    y   -= 0.01;
  }
  }
  return y;
}

Car-HUD Arduino sketch

arduino

1/*
2  This sketch acts as car windscreen HUD (head up display), by Marco  Zonca, 10/2020
3  Arduino Nano as CPU, GPS BT-220 nmea every 1 sec, 3 x buttons,  3 x seven segment displays common cathode,
4  3 x 14511 BCD latch decoder, MPU  EEPROM memory (1 byte) and many resistors;
5
6  WARNING:
7  =======
8  Before  updating software let disconnect RX pin on Arduino (TX from GPS) by the way of the  JUMPER
9*/
10
11#include <Wire.h>
12#include <EEPROM.h>
13
14String inputString  = "";
15String nm_time = "00:00:00";
16String nm_validity = "V";
17String  nm_latitude = "dd°mm.mmmm'N";
18String nm_longitude = "ddd°mm.mmmm'E";
19String  nm_knots = "0.0kn";
20float nmf_knots = 0.0;
21float nmf_kmh = 0.0;
22int nmi_kmh  = 0;
23String nm_truecourse = "360";
24float nmf_truecourse = 360;
25String  nm_date = "dd/mm/yyyy";
26int nmi_truecourse = 0;
27byte kCent = 0;
28byte  kDeci = 0;
29byte kUnit = 0;
30byte tCent = 0;
31byte tDeci = 0;
32byte tUnit  = 0;
33byte brightness = 120;
34byte latch_off = HIGH;
35byte latch_on = LOW;
36int  n=0;
37unsigned long lastmemcheck = 0;
38unsigned long memcheck = 60000;  // check  to save "brightness" value in EEPROM every 60 seconds
39
40bool stringComplete  = false;
41bool isKMH=true;
42bool ret = false;
43
44const int disp001 = 2;  // units display latch
45const int disp010 = 8;  // tens display latch
46const  int disp100 = 12;  // undreds display latch
47
48const int disp001dim = 9;  //  units display dimmer/off pin
49const int disp010dim = 10;  // tens display dimmer/off  pin
50const int disp100dim = 11;  // undreds display dimmer/off pin
51
52const  int button_kt = 14;  // kmh/truecourse button
53const int button_more = 15;  //  brightness + button
54const int button_less = 16;  // brightness - button
55
56const  int degreesLED = 3;  // degrees LED
57
58const int bit_3 = 7;  // bit 3
59const  int bit_2 = 6;  // bit 2
60const int bit_1 = 5;  // bit 1
61const int bit_0 =  4;  // bit 0
62
63const int dly = 10;  // delay latch m/sec
64const byte off  = 0;  // the same as brightness=0
65const int addr = 0; // EEPROM address for brightness  value
66
67const byte numbers[10] [4] = {{0,0,0,0},{1,0,0,0},{0,1,0,0},{1,1,0,0},{0,0,1,0},
68                              {1,0,1,0},{0,1,1,0},{1,1,1,0},{0,0,0,1},{1,0,0,1}};  // bits 0,1,2,3
69
70void setup() {
71  Serial.begin(9600);
72  Wire.begin();
73  inputString.reserve(200);
74  brightness = EEPROM.read(addr);
75  if (brightness  > 250 || brightness < 10) { brightness=120; }  // avoid crazy values from 1st EEPROM  read
76  pinMode(disp001, OUTPUT);
77  pinMode(disp010, OUTPUT);
78  pinMode(disp100,  OUTPUT);
79  pinMode(degreesLED, OUTPUT);
80  pinMode(button_kt, INPUT_PULLUP);
81  pinMode(button_less, INPUT_PULLUP);
82  pinMode(button_more, INPUT_PULLUP);
83  pinMode(bit_3, OUTPUT);
84  pinMode(bit_2, OUTPUT);
85  pinMode(bit_1, OUTPUT);
86  pinMode(bit_0, OUTPUT);  
87  
88  analogWrite(disp001dim, off);  // off and  zero displays
89  analogWrite(disp010dim, off);
90  analogWrite(disp100dim, off);
91  analogWrite(degreesLED, off);
92  
93  setBusNr(0);
94  digitalWrite(disp001,  latch_on);
95  digitalWrite(disp010, latch_on);
96  digitalWrite(disp100, latch_on);
97  delay(dly);
98  digitalWrite(disp001, latch_off);
99  digitalWrite(disp010,  latch_off);
100  digitalWrite(disp100, latch_off);
101
102  analogWrite(disp001dim,  brightness);  // on display
103  analogWrite(disp010dim, brightness);
104  analogWrite(disp100dim,  brightness);
105}  // setup()
106
107void loop() {
108  // GPS NMEA ------------------
109  if (stringComplete == true) {  // received nmea sentence by serial port RX
110    ret = nmeaExtractData();
111    inputString = "";
112    stringComplete =  false;
113    if (ret == true) {
114      kCent=nmi_kmh/100;
115      n=nmi_kmh-(kCent*100);
116      kDeci=n/10;
117      n=nmi_kmh-(kCent*100)-(kDeci*10);
118      kUnit=n;
119      tCent=nmi_truecourse/100;
120      n=nmi_truecourse-(tCent*100);
121      tDeci=n/10;
122      n=nmi_truecourse-(tCent*100)-(tDeci*10);
123      tUnit=n;
124      display();
125    }
126  }
127  if (millis() > (lastmemcheck+memcheck)) {  // put in memory brightness  value (if modified)
128    EEPROM.update(addr,brightness);
129    lastmemcheck=millis();
130  }
131  checkButtons();
132}
133
134void display() {
135  if (isKMH == true) {  // speed in km/h (isKMH=true)
136    analogWrite(degreesLED, off);
137    setBusNr(kUnit);
138    digitalWrite(disp001, latch_on);
139    delay(dly);
140    digitalWrite(disp001,  latch_off);
141    if (kDeci > 0 || kCent > 0) {  // set tens off if tens=0 (and  also undreds=0)
142      setBusNr(kDeci);
143      digitalWrite(disp010, latch_on);
144      delay(dly);
145      digitalWrite(disp010, latch_off);
146      analogWrite(disp010dim,  brightness);
147    } else {
148      analogWrite(disp010dim, off);
149    }
150    if (kCent > 0) {  // set undreds off if=0
151      setBusNr(kCent);
152      digitalWrite(disp100,  latch_on);
153      delay(dly);
154      digitalWrite(disp100, latch_off);
155      analogWrite(disp100dim,  brightness);
156    } else {
157      analogWrite(disp100dim, off);
158    }
159  } else {  // true bearing in degrees (isKMH=false) 
160    analogWrite(degreesLED,  brightness);
161    setBusNr(tUnit);
162    digitalWrite(disp001, latch_on);
163    delay(dly);
164    digitalWrite(disp001, latch_off);
165    if (tDeci > 0 ||  tCent > 0) {  // set tens off if tens=0 (and also undreds=0)
166      setBusNr(tDeci);
167      digitalWrite(disp010, latch_on);
168      delay(dly);
169      digitalWrite(disp010,  latch_off);
170      analogWrite(disp010dim, brightness);
171    } else {
172      analogWrite(disp010dim,  off);
173    }
174    if (tCent > 0) {  // set undreds off if=0
175      setBusNr(tCent);
176      digitalWrite(disp100, latch_on);
177      delay(dly);
178      digitalWrite(disp100,  latch_off);
179      analogWrite(disp100dim, brightness);
180    } else { 
181      analogWrite(disp100dim,  off);
182    }
183  }
184}  // display()
185
186void checkButtons(){
187  if (digitalRead(button_kt)  == LOW) {
188    if (isKMH == true) {
189      isKMH=false;
190    } else {
191      isKMH=true;
192    }
193    delay(250);
194  }
195  if (digitalRead(button_more)  == LOW) {
196    if (brightness <= 240) {
197      brightness=brightness+10;
198    }
199    analogWrite(disp001dim, brightness);
200    analogWrite(disp010dim,  brightness);
201    analogWrite(disp100dim, brightness);
202    delay(100);
203  }
204  if (digitalRead(button_less) == LOW) {
205    if (brightness >= 20) {
206      brightness=brightness-10;
207    }
208    analogWrite(disp001dim, brightness);
209    analogWrite(disp010dim, brightness);
210    analogWrite(disp100dim, brightness);
211    delay(100);
212  }
213}  // checkButtons()
214
215void setBusNr(int number)  {  // sets 4 bits bus
216  for (byte b=0; b<=3; b++) {
217    if (numbers[number][b]==0)  {
218      if (b==0) {digitalWrite(bit_0, LOW);}
219      if (b==1) {digitalWrite(bit_1,  LOW);}
220      if (b==2) {digitalWrite(bit_2, LOW);}
221      if (b==3) {digitalWrite(bit_3,  LOW);}
222    } else {
223      if (b==0) {digitalWrite(bit_0, HIGH);}
224      if  (b==1) {digitalWrite(bit_1, HIGH);}
225      if (b==2) {digitalWrite(bit_2, HIGH);}
226      if (b==3) {digitalWrite(bit_3, HIGH);}
227    }
228  }
229}  // setBusNr()
230
231//  extract data from nmea inputString
232bool nmeaExtractData() {
233  int d=0;
234  int s=0;
235  int y=0;
236  int z=0;
237  float t=0;
238  bool ret = false;  //true  if nmea sentence = $GNRMC and valid CHKSUM
239  if ((inputString.substring(0,6)  == "$GNRMC") && (inputString.substring(inputString.length()-4,inputString.length()-2)  == nmea0183_checksum(inputString))) {
240    y=0;
241    for (s = 1; s < 11; s ++)  { 
242      y=inputString.indexOf(",",y);
243      switch (s) {
244      case  1: //-----------------------time
245        z=inputString.indexOf(",",y+1);
246        if (z>(y+1)) {
247          nm_time=inputString.substring(y+1,y+2+1)+":"+inputString.substring(y+1+2,y+4+1)+":"+inputString.substring(y+1+4,y+6+1);
248        }
249        y=z;
250        break;
251      case 2: //-----------------------validity
252        z=inputString.indexOf(",",y+1);
253        if (z>(y+1)) {
254          nm_validity=inputString.substring(y+1,y+1+1);
255        }
256        y=z;
257        break;
258      case 3: //-----------------------latitude
259        z=inputString.indexOf(",",y+1);
260        if (z>(y+1)) {
261          nm_latitude=inputString.substring(y+1,y+2+1)+"°"+inputString.substring(y+1+2,y+10+1)+"'";
262        }
263        y=z;
264        break;
265      case 4: //-----------------------north/south
266        z=inputString.indexOf(",",y+1);
267        if (z>(y+1)) {
268          nm_latitude=nm_latitude  + inputString.substring(y+1,y+1+1);
269        }
270        y=z;
271        break;
272      case 5: //-----------------------longitude
273        z=inputString.indexOf(",",y+1);
274        if (z>(y+1)) {
275          nm_longitude=inputString.substring(y+1,y+3+1)+"°"+inputString.substring(y+1+3,y+11+1)+"'";
276        }
277        y=z;
278        break;
279      case 6: //-----------------------east/west
280        z=inputString.indexOf(",",y+1);
281        if (z>(y+1)) {
282          nm_longitude=nm_longitude  + inputString.substring(y+1,y+1+1);
283        }
284        y=z;
285        break;
286      case 7:  //-----------------------speed knots
287        z=inputString.indexOf(",",y+1);
288        if (z>(y+1)) {
289          nmf_knots=inputString.substring(y+1,z).toFloat();
290          t=roundOneDec(nmf_knots);
291          nm_knots=String(t,1)+"kn";
292          nmf_kmh=roundTwoDec(nmf_knots * 1.852);
293          nmi_kmh=roundZeroDec(nmf_knots  * 1.852);
294        }
295        y=z;
296        break;
297      case 8: //-----------------------true  course
298        z=inputString.indexOf(",",y+1);
299        if (z>(y+1)) {
300          nmf_truecourse=inputString.substring(y+1,z).toFloat();
301          t=roundZeroDec(nmf_truecourse);
302          nmi_truecourse=t;
303          d=t;
304          nm_truecourse=d;
305        }
306        y=z;
307        break;
308      case 9: //-----------------------date
309        z=inputString.indexOf(",",y+1);
310        if (z>(y+1)) {
311          nm_date=inputString.substring(y+1,y+2+1)+"/"+inputString.substring(y+1+2,y+4+1)+"/20"+inputString.substring(y+1+4,y+6+1);
312        }
313        y=z;
314        break;
315      case 10:
316        // statements  n.u.
317        break;
318      default:
319        // statements n.u.
320        break;
321      }
322    }
323    ret=true;
324  }
325  return ret;
326}  // nmeaExtractData()
327
328/*
329  SerialEvent occurs whenever a new data comes in the hardware serial RX. This
330  routine is run between each time loop() runs, so using delay inside loop can
331  delay response. Multiple bytes of data may be available.
332*/
333void serialEvent()  {
334  while (Serial.available()) {
335    char inChar = (char)Serial.read();
336    inputString += inChar;
337    // if the incoming character is a newline, set  a flag so the main loop can
338    // do something about it
339    if (inChar ==  '\n') {
340      stringComplete = true;
341    }
342  }
343}  // serialEvent()
344
345//calculate  checksum of nmea sentence
346String nmea0183_checksum(String nmea_data) {
347    int  crc = 0;
348    String chSumString = "";
349    int i;
350    // ignore the first  $ sign, checksum in sentence
351    for (i = 1; i < (nmea_data.length()-5); i ++)  { // remove the - 5 if no "*" + cksum + cr + lf are present
352        crc ^=  nmea_data[i];
353    }
354    chSumString = String(crc,HEX);
355    if (chSumString.length()==1)  {
356      chSumString="0"+chSumString.substring(0,1);
357    }
358    chSumString.toUpperCase();
359    return chSumString;
360}  // nmea0183_checksum(String nmea_data)
361
362// round  zero decimals
363float roundZeroDec(float f) {
364  float y, d;
365  y = f*1;
366  d = y - (int)y;
367  y = (float)(int)(f*1)/1;
368  if (d >= 0.5) {
369    y +=  1;
370   } else {
371    if (d < -0.5) {
372    y -= 1;
373  }
374  }
375  return  y;
376}
377
378// round one decimal
379float roundOneDec(float f) {
380  float y,  d;
381  y = f*10;
382  d = y - (int)y;
383  y = (float)(int)(f*10)/10;
384  if (d  >= 0.5) {
385    y += 0.1;
386   } else {
387    if (d < -0.5) {
388    y -= 0.1;
389  }
390  }
391  return y;
392}
393
394// round two decimals
395float roundTwoDec(float  f) {
396  float y, d;
397  y = f*100;
398  d = y - (int)y;
399  y = (float)(int)(f*100)/100;
400  if (d >= 0.5) {
401    y += 0.01;
402   } else {
403    if (d < -0.5) {
404    y  -= 0.01;
405  }
406  }
407  return y;
408}
409

/*
  This sketch acts as car windscreen HUD (head up display), by Marco  Zonca, 10/2020
  Arduino Nano as CPU, GPS BT-220 nmea every 1 sec, 3 x buttons,  3 x seven segment displays common cathode,
  3 x 14511 BCD latch decoder, MPU  EEPROM memory (1 byte) and many resistors;

  WARNING:
  =======
  Before  updating software let disconnect RX pin on Arduino (TX from GPS) by the way of the  JUMPER
*/

#include <Wire.h>
#include <EEPROM.h>

String inputString  = "";
String nm_time = "00:00:00";
String nm_validity = "V";
String  nm_latitude = "dd°mm.mmmm'N";
String nm_longitude = "ddd°mm.mmmm'E";
String  nm_knots = "0.0kn";
float nmf_knots = 0.0;
float nmf_kmh = 0.0;
int nmi_kmh  = 0;
String nm_truecourse = "360";
float nmf_truecourse = 360;
String  nm_date = "dd/mm/yyyy";
int nmi_truecourse = 0;
byte kCent = 0;
byte  kDeci = 0;
byte kUnit = 0;
byte tCent = 0;
byte tDeci = 0;
byte tUnit  = 0;
byte brightness = 120;
byte latch_off = HIGH;
byte latch_on = LOW;
int  n=0;
unsigned long lastmemcheck = 0;
unsigned long memcheck = 60000;  // check  to save "brightness" value in EEPROM every 60 seconds

bool stringComplete  = false;
bool isKMH=true;
bool ret = false;

const int disp001 = 2;  // units display latch
const int disp010 = 8;  // tens display latch
const  int disp100 = 12;  // undreds display latch

const int disp001dim = 9;  //  units display dimmer/off pin
const int disp010dim = 10;  // tens display dimmer/off  pin
const int disp100dim = 11;  // undreds display dimmer/off pin

const  int button_kt = 14;  // kmh/truecourse button
const int button_more = 15;  //  brightness + button
const int button_less = 16;  // brightness - button

const  int degreesLED = 3;  // degrees LED

const int bit_3 = 7;  // bit 3
const  int bit_2 = 6;  // bit 2
const int bit_1 = 5;  // bit 1
const int bit_0 =  4;  // bit 0

const int dly = 10;  // delay latch m/sec
const byte off  = 0;  // the same as brightness=0
const int addr = 0; // EEPROM address for brightness  value

const byte numbers[10] [4] = {{0,0,0,0},{1,0,0,0},{0,1,0,0},{1,1,0,0},{0,0,1,0},
                              {1,0,1,0},{0,1,1,0},{1,1,1,0},{0,0,0,1},{1,0,0,1}};  // bits 0,1,2,3

void setup() {
  Serial.begin(9600);
  Wire.begin();
  inputString.reserve(200);
  brightness = EEPROM.read(addr);
  if (brightness  > 250 || brightness < 10) { brightness=120; }  // avoid crazy values from 1st EEPROM  read
  pinMode(disp001, OUTPUT);
  pinMode(disp010, OUTPUT);
  pinMode(disp100,  OUTPUT);
  pinMode(degreesLED, OUTPUT);
  pinMode(button_kt, INPUT_PULLUP);
  pinMode(button_less, INPUT_PULLUP);
  pinMode(button_more, INPUT_PULLUP);
  pinMode(bit_3, OUTPUT);
  pinMode(bit_2, OUTPUT);
  pinMode(bit_1, OUTPUT);
  pinMode(bit_0, OUTPUT);  
  
  analogWrite(disp001dim, off);  // off and  zero displays
  analogWrite(disp010dim, off);
  analogWrite(disp100dim, off);
  analogWrite(degreesLED, off);
  
  setBusNr(0);
  digitalWrite(disp001,  latch_on);
  digitalWrite(disp010, latch_on);
  digitalWrite(disp100, latch_on);
  delay(dly);
  digitalWrite(disp001, latch_off);
  digitalWrite(disp010,  latch_off);
  digitalWrite(disp100, latch_off);

  analogWrite(disp001dim,  brightness);  // on display
  analogWrite(disp010dim, brightness);
  analogWrite(disp100dim,  brightness);
}  // setup()

void loop() {
  // GPS NMEA ------------------
  if (stringComplete == true) {  // received nmea sentence by serial port RX
    ret = nmeaExtractData();
    inputString = "";
    stringComplete =  false;
    if (ret == true) {
      kCent=nmi_kmh/100;
      n=nmi_kmh-(kCent*100);
      kDeci=n/10;
      n=nmi_kmh-(kCent*100)-(kDeci*10);
      kUnit=n;
      tCent=nmi_truecourse/100;
      n=nmi_truecourse-(tCent*100);
      tDeci=n/10;
      n=nmi_truecourse-(tCent*100)-(tDeci*10);
      tUnit=n;
      display();
    }
  }
  if (millis() > (lastmemcheck+memcheck)) {  // put in memory brightness  value (if modified)
    EEPROM.update(addr,brightness);
    lastmemcheck=millis();
  }
  checkButtons();
}

void display() {
  if (isKMH == true) {  // speed in km/h (isKMH=true)
    analogWrite(degreesLED, off);
    setBusNr(kUnit);
    digitalWrite(disp001, latch_on);
    delay(dly);
    digitalWrite(disp001,  latch_off);
    if (kDeci > 0 || kCent > 0) {  // set tens off if tens=0 (and  also undreds=0)
      setBusNr(kDeci);
      digitalWrite(disp010, latch_on);
      delay(dly);
      digitalWrite(disp010, latch_off);
      analogWrite(disp010dim,  brightness);
    } else {
      analogWrite(disp010dim, off);
    }
    if (kCent > 0) {  // set undreds off if=0
      setBusNr(kCent);
      digitalWrite(disp100,  latch_on);
      delay(dly);
      digitalWrite(disp100, latch_off);
      analogWrite(disp100dim,  brightness);
    } else {
      analogWrite(disp100dim, off);
    }
  } else {  // true bearing in degrees (isKMH=false) 
    analogWrite(degreesLED,  brightness);
    setBusNr(tUnit);
    digitalWrite(disp001, latch_on);
    delay(dly);
    digitalWrite(disp001, latch_off);
    if (tDeci > 0 ||  tCent > 0) {  // set tens off if tens=0 (and also undreds=0)
      setBusNr(tDeci);
      digitalWrite(disp010, latch_on);
      delay(dly);
      digitalWrite(disp010,  latch_off);
      analogWrite(disp010dim, brightness);
    } else {
      analogWrite(disp010dim,  off);
    }
    if (tCent > 0) {  // set undreds off if=0
      setBusNr(tCent);
      digitalWrite(disp100, latch_on);
      delay(dly);
      digitalWrite(disp100,  latch_off);
      analogWrite(disp100dim, brightness);
    } else { 
      analogWrite(disp100dim,  off);
    }
  }
}  // display()

void checkButtons(){
  if (digitalRead(button_kt)  == LOW) {
    if (isKMH == true) {
      isKMH=false;
    } else {
      isKMH=true;
    }
    delay(250);
  }
  if (digitalRead(button_more)  == LOW) {
    if (brightness <= 240) {
      brightness=brightness+10;
    }
    analogWrite(disp001dim, brightness);
    analogWrite(disp010dim,  brightness);
    analogWrite(disp100dim, brightness);
    delay(100);
  }
  if (digitalRead(button_less) == LOW) {
    if (brightness >= 20) {
      brightness=brightness-10;
    }
    analogWrite(disp001dim, brightness);
    analogWrite(disp010dim, brightness);
    analogWrite(disp100dim, brightness);
    delay(100);
  }
}  // checkButtons()

void setBusNr(int number)  {  // sets 4 bits bus
  for (byte b=0; b<=3; b++) {
    if (numbers[number][b]==0)  {
      if (b==0) {digitalWrite(bit_0, LOW);}
      if (b==1) {digitalWrite(bit_1,  LOW);}
      if (b==2) {digitalWrite(bit_2, LOW);}
      if (b==3) {digitalWrite(bit_3,  LOW);}
    } else {
      if (b==0) {digitalWrite(bit_0, HIGH);}
      if  (b==1) {digitalWrite(bit_1, HIGH);}
      if (b==2) {digitalWrite(bit_2, HIGH);}
      if (b==3) {digitalWrite(bit_3, HIGH);}
    }
  }
}  // setBusNr()

//  extract data from nmea inputString
bool nmeaExtractData() {
  int d=0;
  int s=0;
  int y=0;
  int z=0;
  float t=0;
  bool ret = false;  //true  if nmea sentence = $GNRMC and valid CHKSUM
  if ((inputString.substring(0,6)  == "$GNRMC") && (inputString.substring(inputString.length()-4,inputString.length()-2)  == nmea0183_checksum(inputString))) {
    y=0;
    for (s = 1; s < 11; s ++)  { 
      y=inputString.indexOf(",",y);
      switch (s) {
      case  1: //-----------------------time
        z=inputString.indexOf(",",y+1);
        if (z>(y+1)) {
          nm_time=inputString.substring(y+1,y+2+1)+":"+inputString.substring(y+1+2,y+4+1)+":"+inputString.substring(y+1+4,y+6+1);
        }
        y=z;
        break;
      case 2: //-----------------------validity
        z=inputString.indexOf(",",y+1);
        if (z>(y+1)) {
          nm_validity=inputString.substring(y+1,y+1+1);
        }
        y=z;
        break;
      case 3: //-----------------------latitude
        z=inputString.indexOf(",",y+1);
        if (z>(y+1)) {
          nm_latitude=inputString.substring(y+1,y+2+1)+"°"+inputString.substring(y+1+2,y+10+1)+"'";
        }
        y=z;
        break;
      case 4: //-----------------------north/south
        z=inputString.indexOf(",",y+1);
        if (z>(y+1)) {
          nm_latitude=nm_latitude  + inputString.substring(y+1,y+1+1);
        }
        y=z;
        break;
      case 5: //-----------------------longitude
        z=inputString.indexOf(",",y+1);
        if (z>(y+1)) {
          nm_longitude=inputString.substring(y+1,y+3+1)+"°"+inputString.substring(y+1+3,y+11+1)+"'";
        }
        y=z;
        break;
      case 6: //-----------------------east/west
        z=inputString.indexOf(",",y+1);
        if (z>(y+1)) {
          nm_longitude=nm_longitude  + inputString.substring(y+1,y+1+1);
        }
        y=z;
        break;
      case 7:  //-----------------------speed knots
        z=inputString.indexOf(",",y+1);
        if (z>(y+1)) {
          nmf_knots=inputString.substring(y+1,z).toFloat();
          t=roundOneDec(nmf_knots);
          nm_knots=String(t,1)+"kn";
          nmf_kmh=roundTwoDec(nmf_knots * 1.852);
          nmi_kmh=roundZeroDec(nmf_knots  * 1.852);
        }
        y=z;
        break;
      case 8: //-----------------------true  course
        z=inputString.indexOf(",",y+1);
        if (z>(y+1)) {
          nmf_truecourse=inputString.substring(y+1,z).toFloat();
          t=roundZeroDec(nmf_truecourse);
          nmi_truecourse=t;
          d=t;
          nm_truecourse=d;
        }
        y=z;
        break;
      case 9: //-----------------------date
        z=inputString.indexOf(",",y+1);
        if (z>(y+1)) {
          nm_date=inputString.substring(y+1,y+2+1)+"/"+inputString.substring(y+1+2,y+4+1)+"/20"+inputString.substring(y+1+4,y+6+1);
        }
        y=z;
        break;
      case 10:
        // statements  n.u.
        break;
      default:
        // statements n.u.
        break;
      }
    }
    ret=true;
  }
  return ret;
}  // nmeaExtractData()

/*
  SerialEvent occurs whenever a new data comes in the hardware serial RX. This
  routine is run between each time loop() runs, so using delay inside loop can
  delay response. Multiple bytes of data may be available.
*/
void serialEvent()  {
  while (Serial.available()) {
    char inChar = (char)Serial.read();
    inputString += inChar;
    // if the incoming character is a newline, set  a flag so the main loop can
    // do something about it
    if (inChar ==  '\n') {
      stringComplete = true;
    }
  }
}  // serialEvent()

//calculate  checksum of nmea sentence
String nmea0183_checksum(String nmea_data) {
    int  crc = 0;
    String chSumString = "";
    int i;
    // ignore the first  $ sign, checksum in sentence
    for (i = 1; i < (nmea_data.length()-5); i ++)  { // remove the - 5 if no "*" + cksum + cr + lf are present
        crc ^=  nmea_data[i];
    }
    chSumString = String(crc,HEX);
    if (chSumString.length()==1)  {
      chSumString="0"+chSumString.substring(0,1);
    }
    chSumString.toUpperCase();
    return chSumString;
}  // nmea0183_checksum(String nmea_data)

// round  zero decimals
float roundZeroDec(float f) {
  float y, d;
  y = f*1;
  d = y - (int)y;
  y = (float)(int)(f*1)/1;
  if (d >= 0.5) {
    y +=  1;
   } else {
    if (d < -0.5) {
    y -= 1;
  }
  }
  return  y;
}

// round one decimal
float roundOneDec(float f) {
  float y,  d;
  y = f*10;
  d = y - (int)y;
  y = (float)(int)(f*10)/10;
  if (d  >= 0.5) {
    y += 0.1;
   } else {
    if (d < -0.5) {
    y -= 0.1;
  }
  }
  return y;
}

// round two decimals
float roundTwoDec(float  f) {
  float y, d;
  y = f*100;
  d = y - (int)y;
  y = (float)(int)(f*100)/100;
  if (d >= 0.5) {
    y += 0.01;
   } else {
    if (d < -0.5) {
    y  -= 0.01;
  }
  }
  return y;
}

Downloadable files

Sketch version 2 (read instructions first)

Sketch version 2.2 (read instructions first)

PCB #1 (components face)