GPS GP-735 ttl unit- how to increase the update rate

GPS/GNSS Development Boards
1

I have a Sparkfun gp-735 receiver.

It is the non usb, ttl version.

I have interfaced it to an Arduino.

It is advertised as a 1Hz device which “can be increased to 10Hz if you need”

I would like to increase the sample rate.

The documentation is less than helpful.

The required command is not specified:

“Update rate: 1 Hz (default), up to 10Hz by enabling command”

The sentence ends there!

The method for sending ttl instructions is not mentioned.

Please advise on the command and Arduino procedure.

2

Hi drp.

Unfortunately we don’t have a list of commands for this, but the [GPS Evaluation Software can send the correct binary command to change the update rate.

By spying on the data coming from the evaluation software, I was able to determine what binary bytes to send to switch between 1Hz and 10. Both are listed below.

Change to 10Hz
B5 62 06 08 06 00 64 00 01 00 01 00 7A 12 B5 62 06 08 00 00 0E 30

Change to 1Hz
B5 62 06 08 06 00 E8 03 01 00 01 00 01 39 B5 62 06 08 00 00 0E 30

You will need to send these as HEX bytes in Arduino in order for the GPS to recognize the commands. The Serial.write command should do the trick.](u-center)

3

Hello TS-Chris,

Thanks for the prompt response.

Does the GPS evaluation software work with the ttl gp-735 and if so, how?

Can you provide details for other available rates between 1 and 10HZ?

David

4

Hi David.

Does the GPS evaluation software work with the ttl gp-735 and if so, how?

Yes, the software does work with the GP-735. That's how I was able obtain the hex stings from my last post and verify they worked. Pressing F1 (help) in the software directs you to the home page for the software and the users guide can be found there. The link below will take you to the users guide.
  • - [[u-centerGNSS evaluation software for WindowsUser Guide](https://www.u-blox.com/sites/default/files/u-center_UserGuide_%28UBX-13005250%29.pdf)
    • [/list]

    Everything you should need to know about the software would be covered there. You would need a FTDI Breakout (or another USB to serial converter) to connect the GPS to your computer. That’s the interface that allows the software to communicate with the GPS.

    Can you provide details for other available rates between 1 and 10HZ?

    I tried 1, 5 and 10Hz and all three of those worked. There may be other rates that work as well but I didn't try them](https://www.u-blox.com/sites/default/files/u-center_UserGuide_%28UBX-13005250%29.pdf)
    5

    Hi,

    I have written a small sketch to allow the ttl gps to pass through the arduino:

    #define GPS_BAUD  9600  // GP-735 default baud rate
#include <TinyGPS++.h>
#include <SoftwareSerial.h>
TinyGPSPlus gps;
#define RX_PIN  4 // GPS TX
#define TX_PIN  5 // GPS RX
#define LED_PIN 7 // GPS Fix LED
SoftwareSerial ss(RX_PIN,TX_PIN);

void setup() {
Serial.begin(GPS_BAUD);
ss.begin(GPS_BAUD);
pinMode(LED_PIN,OUTPUT);  // on board pin
}

void loop() {
  if(gps.location.isValid()){
  digitalWrite(LED_PIN,HIGH);
  }else{
  digitalWrite(LED_PIN,LOW);
  }
  while(Serial.available()>0){
  ss.write(Serial.read());
  }
  while(ss.available()>0){
  byte g= ss.read();
  Serial.write(g);
  gps.encode(g); 
  }
}

    Once uploaded the arduino ide must be closed to allow the u-center-GNSS software access to the arduino comport.

    With this I can use all the u-center fuctions.

    Without battery backup, it appears any uploaded gps settings are lost after power removal. I note that backup battery connections are present on the mini gps shield.

    I used this method to upload settings in a sketch:

    const byte twoHz[]= { 
0xB5,0x62,0x06,0x08,0x06,0x00, 0xF4,0x01, 0x01,0x00,0x01,0x00, 0x0B,0x77,
0xB5,0x62,0x06,0x08,0x00,0x00,0x0E,0x30,
0xB5, 0x62, 0x06, 0x09, 0x0D, 0x00, 0x00, 0x00, 0x00, 0x00, 0xFF, 0xFF,0x00, 0x00, 0x00,0x00,
0x00, 0x00, 0x03, 0x1D, 0xAB                      
};
// the last 2 byte lines of twoHz save the configuration ( if required).
#include <SoftwareSerial.h>
#define RX_PIN  4 // GPS TX
#define TX_PIN  5 // GPS RX
#define GPS_BAUD  9600  // GP-735 default baud rate
SoftwareSerial ss(RX_PIN,TX_PIN);
ss.begin(GPS_BAUD); // Begin serial communication with GPS

  for (byte i=0; i <sizeof(twoHz); i++) {
  ss.write(twoHz[i]);
  }

    Others may find this helpful. (Particulary in the hookup guide)

    Feel free to use it as you want.

    David

    6

    Thanks for sharing that David! I’m sure this will be helpful for others. :slight_smile: