Get GPS position from a Heltec Wireless Tracker arduino

Question

I've bought a Heltec Wireless Tracker Arduino.

I want to get the GPS position. I've taken the original example "GPSDisplayOnTFT" from the IDE (I've made a few changes because the original code wasn't working for me).

Example from IDE

My screen always shows:

peek: 0
LAT: 0.00
valid: 0

I've put a comment on the code to show the line.

This is my code:

#include "Arduino.h"
#include "HT_st7735.h"
#include "HT_TinyGPS++.h"
TinyGPSPlus GPS;
HT_st7735 st7735;
#define VGNSS_CTRL 3
void GPS_test(void)
{
 Serial.println("GPS 1");
 Serial1.begin(9600,SERIAL_8N1,33,34); 
 Serial.println("GPS_test");
 delay(1000);
 while(1)
 {
 st7735.st7735_fill_screen(ST7735_BLACK);
 if(Serial1.available()>0)
 {
 if(Serial1.peek()!='\n')
 {
 GPS.encode(Serial1.read());
 String peek = "peek: " + (String)GPS.encode(Serial1.read());
 Serial.println(peek);
 st7735.st7735_write_str(0, 0, peek);
 
 }
 else
 {
 Serial1.read();
 if(GPS.time.second()==0)
 {
 Serial.println("second==0");
 continue;
 }
 st7735.st7735_fill_screen(ST7735_BLACK);
 st7735.st7735_write_str(0, 0, (String)"GPS_test");
 String time_str = (String)GPS.time.hour() + ":" + (String)GPS.time.minute() + ":" + (String)GPS.time.second()+ ":"+(String)GPS.time.centisecond();
 st7735.st7735_write_str(0, 20, time_str);
 Serial.println(time_str);
 String latitude = "LAT: " + (String)GPS.location.lat();
 st7735.st7735_write_str(0, 40, latitude);
 Serial.println(latitude);
 String longitude = "LON: "+ (String)GPS.location.lng();
 st7735.st7735_write_str(0, 60, longitude);
 Serial.println(longitude);
 
 delay(5000);
 while(Serial1.read()>0);
 }
 Serial.println("***************************");
 Serial.println(Serial1.peek());
 Serial.println(Serial1.read());
 Serial.println(GPS.location.lat());
 st7735.st7735_write_str(0, 20, "LAT: " + (String)GPS.location.lat());
 //NOTE: it always shows '0'
 st7735.st7735_write_str(0, 40, "valid: " + (String)GPS.satellites.isValid());
 Serial.println("*********** fin ***********");
 }
 else{
 Serial.println("Serial 1 no available"); 
 st7735.st7735_fill_screen(ST7735_BLACK);
 st7735.st7735_write_str(10, 50, (String)"Unavailable");
 delay(5000);
 }
 Serial.println("while 1");
 delay(5000);
 }
}
void setup(){
 delay(100);
 Serial.begin(115200);
 Serial.println("setup 1");
 pinMode(VGNSS_CTRL,OUTPUT);
 digitalWrite(VGNSS_CTRL,LOW);
 
 st7735.st7735_init();
 st7735.st7735_fill_screen(ST7735_BLACK);
 st7735.st7735_write_str(20, 10, (String)"Loading ...");
 st7735.st7735_write_str(20, 50, (String)"GPS_test");
 Serial.println("setup 2");
 GPS_test();
 Serial.println("setup 3");
}
void loop(){
 Serial.println("loop 1");
 delay(3000);
 Serial.println("loop 2");
}

I'm not sure if I have to connect the antenna to the GNSS module.

Is there something I can print in thelogs to bring more info?

========= EDITED =========

This is the serial monitor output:

01:13:43.526 -> GPS_test started
01:18:12.693 -> setup 1
01:18:12.871 -> setup 2
01:18:12.871 -> GPS 1
01:18:12.904 -> GPS_test
01:18:14.201 -> peek: 0
01:18:14.232 -> ***************************
01:18:14.232 -> 106
01:18:14.232 -> 106
01:18:14.232 -> 0.00
01:18:14.329 -> *********** fin ***********
01:18:14.329 -> while 1
01:18:19.610 -> peek: 0
01:18:19.685 -> ***************************
01:18:19.685 -> 79
01:18:19.685 -> 79
01:18:19.685 -> 0.00
01:18:19.738 -> *********** fin ***********
01:18:19.738 -> while 1
01:18:25.036 -> peek: 0

• jsotola: what does this mean? ... original code wasn't working for me
• Jaime Roman: @jsotola, it means that serial monitor and screen were showing nothing.
• dda: "I'm not sure if I have to connect the antenna to the GNSS module." Without an antenna, how is the module supposed to receive signals from space?

Answer 1

#define VGNSS_CTRL 3

Based on the example code from Heltec Github page. The pin for VGNSS_Ctrl is pin 37 instead of pin 3 as shown in your code.

Further checking the schematic diagram for Heltec Wireless Tracker V1.0, it confirmed that VGNSS_Ctrl is indeed on pin 37 which is used to activate the VDD_GNSS (i.e. to enable the power supply for GPS module).

enter image description here

• Petr Novak: Hcheung solution is nearly correct, but the pin according schematic is not 37 but 36.
• stuartb: @PetrNovak No I think 37 is correct for VGNSS_CTRL on v1.0 which is the schematic shown here. They removed VGNSS_CTRL in v1.1 and replaced it with VEXT which is now pin 7.

Answer 2

Many COTS GNSS modules, when not in lock, send NMEA message with just commas where latitude and longitude are expected.

The UC6580, used on the Heltec Wireless Tracker, appears to use the NMEA 0183 data format.

As the NMEA messages do not appear in the posted code, it is assumed some or all are in the TinyGPSPlus library used in the above code.

If we go to the TinyGPSPlus github.com account we see there are example Arduino INO file. This example tracks multiple satellites and reports "Satellite numbers, elevation, azimuth, and signal-to-noise ratio". This data is usually available even before the GNSS module is in lock (producing latitude and longitude values). So it's useful during problem investigation.

Modify the question when more information is available. For now it sounds like a bad GNSS module, bad GNSS antenna, bad antenna connection or you are indoors where you can not see GNSS satellites.