In this video lesson we show how you can get extremely accurate time reference from your Adafruit Ultimate GPS V3. We show that atomic clock time is encoded in the NMEA sentences, and is in UTC. We show how to retrieve the data, and convert to your local time. In this video I compensated for the clock rolling from one day to the next, for positive UTC correction time, but did not account for clock rollover for negative UTC correction times. Also, several pointed out that you have to also compensate for calendar rollover at the end of the month, and the end of the year. The video shows how we are approaching the problem, and then the code below includes the compensations we did not do in the video. The code is heavily commented so hopefully you will be able to follow it.
For your convenience, the code developed in the lesson is presented below:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 | from machine import Pin, I2C, UART import time import _thread from ssd1306 import SSD1306_I2C # This is my utc correction. You need to look yours # up for your location utcCorrect = 3 i2c2 = I2C(1, sda=Pin(2), scl=Pin(3), freq=400000) dsp = SSD1306_I2C(128, 64, i2c2) dataLock = _thread.allocate_lock() keepRunning = True GPS = UART(1, baudrate=9600, tx=machine.Pin(8), rx=machine.Pin(9)) # The following line ensures that the GPS reports the GPVTG NMEA Sentence GPS.write(b"$PMTK314,0,1,1,1,1,1,1,0,0,0,0,0,0,0,0,0,0,0,0*28\r\n") NMEAdata = { 'GPGGA': "", 'GPGSA': "", 'GPRMC': "", 'GPVTG': "" } GPSdata = { 'latDD': 0, 'lonDD': 0, 'heading': 0, 'fix': False, 'sats': 0, 'knots': 0, 'time': '00:00:00', 'date': '00/00/0000' } def gpsThread(): print("Thread Running") global keepRunning, NMEAdata GPGGA = "" GPGSA = "" GPRMC = "" GPVTG = "" while not GPS.any(): pass while GPS.any(): junk = GPS.read() print(junk) myNMEA = "" while keepRunning: if GPS.any(): myChar = GPS.read(1).decode('utf-8') myNMEA = myNMEA + myChar if myChar == '\n': myNMEA = myNMEA.strip() if myNMEA[1:6] == "GPGGA": GPGGA = myNMEA if myNMEA[1:6] == "GPGSA": GPGSA = myNMEA if myNMEA[1:6] == "GPRMC": GPRMC = myNMEA if myNMEA[1:6] == "GPVTG": GPVTG = myNMEA if GPGGA != "" and GPGSA != "" and GPRMC != "" and GPVTG != "": dataLock.acquire() NMEAdata = { 'GPGGA': GPGGA, 'GPGSA': GPGSA, 'GPRMC': GPRMC, 'GPVTG': GPVTG } dataLock.release() myNMEA = "" print("Thread Terminated Cleanly") def parseGPS(): readFix = int(NMEAmain['GPGGA'].split(',')[6]) if readFix != 0: GPSdata['fix'] = True latRAW = NMEAmain['GPGGA'].split(',')[2] latDD = int(latRAW[0:2]) + float(latRAW[2:]) / 60 if NMEAmain['GPGGA'].split(',')[3] == 'S': latDD = -latDD GPSdata['latDD'] = latDD lonRAW = NMEAmain['GPGGA'].split(',')[4] lonDD = int(lonRAW[0:3]) + float(lonRAW[3:]) / 60 if NMEAmain['GPGGA'].split(',')[5] == 'W': lonDD = -lonDD GPSdata['lonDD'] = lonDD heading = float(NMEAmain['GPRMC'].split(',')[8]) GPSdata['heading'] = heading knots = float(NMEAmain['GPRMC'].split(',')[7]) GPSdata['knots'] = knots sats = int(NMEAmain['GPGGA'].split(',')[7]) GPSdata['sats'] = sats utcTime = NMEAmain['GPGGA'].split(',')[1] utcDate = NMEAmain['GPRMC'].split(',')[9] # utcTime = "013445.000" # utcDate = "010125" # Extract year from UTC date (format: DDMMYY), prepend '20' for full year (e.g., '25' → '2025') myYear = '20' + utcDate[4:] # Extract month from UTC date (e.g., '01' for January) myMonth = utcDate[2:4] # Extract day from UTC date (e.g., '01' for 1st) myDay = utcDate[0:2] # Calculate hours by adding UTC offset to UTC hours, convert to string myHours = str(int(utcTime[0:2]) + utcCorrect) # Extract minutes from UTC time (e.g., '34' from '013445.000') myMin = utcTime[2:4] # Extract seconds from UTC time (e.g., '45' from '013445.000') mySec = utcTime[4:6] # Define array of maximum days per month (index 0-11 for months 1-12: Jan to Dec) maxDays = ['31', '28', '31', '30', '31', '30', '31', '31', '30', '31', '30', '31'] # Check if year is a leap year (simplified: divisible by 4); if so, set February to 29 days if int(myYear) % 4 == 0: maxDays[1] = '29' # Check if hours exceed 24 (for positive UTC offsets, e.g., UTC 22:00 + 5 = 27:00) if int(myHours) >= 24: # Subtract 24 from hours to wrap around to next day (e.g., 27 → 3) myHours = str(int(myHours) - 24) # Pad hours with leading zero if single digit (e.g., '3' → '03') if len(myHours) < 2: myHours = '0' + myHours # Increment day to account for crossing midnight (e.g., 30 → 31) myDay = str(int(myDay) + 1) # Check if day exceeds maximum days for the current month (e.g., June 31 > 30) if int(myDay) > int(maxDays[int(myMonth) - 1]): # Reset day to 1 for the next month myDay = '01' # Increment month (e.g., June → July) myMonth = str(int(myMonth) + 1) # Check if month exceeds 12 (e.g., December → January) if int(myMonth) > 12: # Reset month to January myMonth = '01' # Increment year (e.g., 2025 → 2026) myYear = str(int(myYear) + 1) # Pad day with leading zero if single digit (e.g., '1' → '01') if len(myDay) < 2: myDay = '0' + myDay # Pad month with leading zero if single digit (e.g., '7' → '07') if len(myMonth) < 2: myMonth = '0' + myMonth # Check if hours are negative (for negative UTC offsets, e.g., UTC 01:00 - 5 = -4) if int(myHours) < 0: # Add 24 to hours to wrap around to previous day (e.g., -4 → 20) myHours = str(int(myHours) + 24) # Pad hours with leading zero if single digit (e.g., '3' → '03') if len(myHours) < 2: myHours = '0' + myHours # Decrement day to account for crossing midnight backward (e.g., 01 → 00) myDay = str(int(myDay) - 1) # Check if day is less than 1 (e.g., January 1 → December 31) if int(myDay) < 1: # Decrement month (e.g., January → December) myMonth = str(int(myMonth) - 1) # Check if month is less than 1 (e.g., January → December of previous year) if int(myMonth) < 1: # Set month to December myMonth = '12' # Decrement year (e.g., 2025 → 2024) myYear = str(int(myYear) - 1) # Set day to maximum days of the new month (e.g., December → 31) myDay = maxDays[int(myMonth) - 1] # Pad day with leading zero if single digit (e.g., '1' → '01') if len(myDay) < 2: myDay = '0' + myDay # Pad month with leading zero if single digit (e.g., '7' → '07') if len(myMonth) < 2: myMonth = '0' + myMonth # Combine hours, minutes, seconds into time string (e.g., '20:34:45') myTime = myHours + ':' + myMin + ':' + mySec # Combine month, day, year into date string (e.g., '12/31/2024') myDate = myMonth + '/' + myDay + '/' + myYear # Store local time in GPSdata dictionary GPSdata['time'] = myTime # Store local date in GPSdata dictionary GPSdata['date'] = myDate def dispOLED(): dsp.fill(0) if GPSdata['fix'] == False: dsp.text("Waiting for a fix . . .", 0, 0) if GPSdata['fix'] == True: dsp.text(GPSdata['date'][0:5] + ' ' + GPSdata['time'], 0, 0) dsp.text("LAT: " + str(GPSdata['latDD']), 0, 16) dsp.text("LON: " + str(GPSdata['lonDD']), 0, 26) dsp.text("SATS: " + str(GPSdata['sats']), 0, 56) dsp.text("SPEED: " + str(GPSdata['knots']) + ' Knts', 0, 36) dsp.text("HEAD: " + str(GPSdata['heading']) + 'deg.', 0, 46) dsp.show() _thread.start_new_thread(gpsThread, ()) time.sleep(3) try: while True: dataLock.acquire() NMEAmain = NMEAdata.copy() dataLock.release() parseGPS() if GPSdata['fix'] == False: print("Waiting for Fix . . .") if GPSdata['fix'] == True: print("Ultimate GPS Tracker Report: ") print(GPSdata['time'], GPSdata['date']) print("Lat and Lon: ", GPSdata['latDD'], GPSdata['lonDD']) print("Knots: ", GPSdata['knots']) print("Heading: ", GPSdata['heading']) print("Sats: ", GPSdata['sats']) print() dispOLED() time.sleep(1) except KeyboardInterrupt: print("\nStopping Program . . . Cleaning Up UART") keepRunning = False time.sleep(1) GPS.deinit() time.sleep(1) dsp.fill(0) dsp.show() print("Exited Cleanly") |