Issues with Wemos D1 mini esp8266 and a GPS

Using Arduino Programming Questions
#1

Hi so I'm currently trying to program an ESP8266 Wemos d1 mini to read a GPS but it's not comming up with any values. I'm using a GP-20U7 for the GPS. Currently my code is this:

#include "SoftwareSerial.h"
#include "TinyGPS++.h"

SoftwareSerial ss(2, 0);
//SoftwareSerial ss(3, 1);
//SoftwareSerial ss(9, 10);

TinyGPSPlus gps;

void setup() {
pinMode(2, INPUT);
pinMode(0, OUTPUT);
Serial.begin(115200);
Serial.print("Testing");
ss.begin(115200);
}

// the loop function runs over and over again forever
void loop() {
int reading;
int encoding;
delay(100);
while (ss.available() > 0){
reading = ss.read();
encoding = gps.encode(reading);
}
Serial.println("READ: ");
Serial.println(reading);
Serial.println("ENCODE: ");
Serial.println(encoding);
Serial.print("LAT="); Serial.print(gps.location.lat(), 6);
Serial.print(" LNG="); Serial.println(gps.location.lng(), 6);
}

I have the GPS TX connected to D4 on the Wemos currently (GPIO 0)

#2

I have not checked what it means for you but would suggest to not use numbers for the pins, use [b]D[/b][color=blue]xx[/color] based on the pin mapping definition (see /d1_mini/pins_arduino.h)

Also have you translated to get a 3V Rx from the 5V Tx possibly from your GPS?

#3

J-M-L:
I have not checked what it means for you but would suggest to not use numbers for the pins, use [b]D[/b][color=blue]xx[/color] based on the pin mapping definition (see /d1_mini/pins_arduino.h)

Also have you translated to get a 3V Rx from the 5V Tx possibly from your GPS?

Thanks, so the Tx from the GPS is also 3.3V

#4

MapleSyrup654:
Thanks, so the Tx from the GPS is also 3.3V

OK - that's good.

I have the GPS TX connected to D4 on the Wemos currently (GPIO 0)

I'm on a computer now so easier. when you doSoftwareSerial ss(2, 0);that is the equivalent of SoftwareSerial ss(D4, D3); where rxPin = D4 (the pin on which to receive serial data) and txPin = D3 (the pin on which to transmit serial data). So seems this is fine.

--> have you joined grounds from your GPS and Wemos?

You don't need this, this is done by the SoftwareSerial code in the right way when you create your instance

  pinMode(2, INPUT);
  pinMode(0, OUTPUT);
#5

Thanks, our ground ares connected though. It works if I set the serial pin to anything other than Rx, but when i use Rx to receive, it doesn't thing there is a GPS. It's important for my project that I do use the Rx pin though.

#6

MapleSyrup654:
Thanks, our ground ares connected though. It works if I set the serial pin to anything other than Rx, but when i use Rx to receive, it doesn’t thing there is a GPS. It’s important for my project that I do use the Rx pin though.

what do you mean by Rx ?? if this is the hardware serial then it’s in use by your computer when you open the Serial console…

#7

The problem is using delay and printing too much. So many libraries’ examples have led users down this dead-end path.

Here is a sketch that shows how many times loop gets called while waiting for each GPS update (1 second):

#include "SoftwareSerial.h"
#include <NMEAGPS.h>

SoftwareSerial gpsPort(2, 0);
//SoftwareSerial gpsPort(3, 1);
//SoftwareSerial gpsPort(9, 10);

NMEAGPS gps;

void setup() {
  pinMode(2, INPUT);
  pinMode(0, OUTPUT);

  Serial.begin(115200);
  Serial.println("Testing");

  gpsPort.begin(115200);
}


unsigned long loopCount     = 0;
unsigned long lastCharCount = 0;


void loop()
{

  // This isn't really necessary, but it shows
  //   how *few* times a character is ready to be read.
  loopCount++;

  // Check for available GPS chars and parse them.
  if (gps.available( gpsPort )) {

    // Exactly once per second, a complete fix structure is ready to read.
    //   This structure contains all parsed GPS fields.
    gps_fix fix = gps.read();

    Serial.print( "READ characters: " );
    Serial.println( gps.statistics.chars - lastCharCount );
    lastCharCount = gps.statistics.chars;

    Serial.print("CALLS to loop: ");
    Serial.println( loopCount );
    loopCount = 0;

    Serial.print("LAT=");
    if (fix.valid.location) {
      Serial.print( fix.latitude(), 6 );
    }

    Serial.print(" LNG=");
    if (fix.valid.location) {
      Serial.print( fix.longitude(), 6 );
    }

    Serial.println();
  }
}

On a 20MHz Mega, loop gets called ~150000 times per second, to read about 450 characters. When you delay for 100ms, the GPS device has time to send 1152 characters (at 115200 baud). Because the input buffer only has room for 64 character, most of the GPS characters will get ignored.

The secondary issue is that you are printing on every call to loop. The output buffer has room for only 64 characters. After a few iterations through loop, the output buffer is full, and those prints cause your sketch to wait for the previous characters to be transmitted (~86us per character). While waiting for the prints to go out, the GPS device continues to send characters. This will also cause the input buffer to overflow, losing more GPS characters.

The above sketch uses my NeoGPS library, which is smaller, faster, more accurate and more reliable than all other GPS libraries. There are many examples to show the correct program structure, and it supports many data fields. Even if you don’t use it, be sure the read the tips on the Installation and Troubleshooting pages.

Also notice that it does not try to use an invalid location. The GPS device may not know the location, so your sketch should not try to print an invalid location when you don’t have good satellite reception.

NeoGPS is available from the Arduino Library Manager, under the IDE menu Sketch → Include Library → Manage Libraries.

Cheers!

#8