Ava High Altitude Balloon Project

Ok firstly we need to switch the RX&TX connections over on the board as we were passing through to the in board Serial to USB chip. This is important, don’t do this and nothing will work

So amend the wiring as follows :

Arduino 5V to GPS Board 5V
Arduino GND to GPS Board GND
Arduino Pin 0 (RX) to GPS Board TX
Arduino Pin 1 (TX) to GPS Board RX
Arduino Pin 2 to GPS Board EN

Load the following code up on your Arduino (close down U-Center at this point as it will be hanging on to the serial port).  This code is derived from Jon Sowman and Joey flight computer CUSF https://github.com/cuspaceflight/joey-m/tree/master/firmware

This code opens the serial port, send the binary command to set the dynamic model, waits for confirmation this has been acknowledged by the GPS. Once done it just drops to the main loop where it just blinks the Status LED once a second to indicate success.

#include <util/delay.h>

#define GPSENABLE 2
#define STATUSLED 13

void setup() {
 pinMode(GPSENABLE, OUTPUT);
 pinMode(STATUSLED, OUTPUT);
 Serial.begin(9600);
 _delay_ms(500);
 digitalWrite(GPSENABLE, HIGH);
 _delay_ms(500);
 setGPS_DynamicModel6();
}
void loop() {
 digitalWrite(STATUSLED,!digitalRead(STATUSLED));
 _delay_ms(1000);
}
void setGPS_DynamicModel6()
{
 int gps_set_sucess=0;
 uint8_t setdm6[] = {
 0xB5, 0x62, 0x06, 0x24, 0x24, 0x00, 0xFF, 0xFF, 0x06,
 0x03, 0x00, 0x00, 0x00, 0x00, 0x10, 0x27, 0x00, 0x00,
 0x05, 0x00, 0xFA, 0x00, 0xFA, 0x00, 0x64, 0x00, 0x2C,
 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x16, 0xDC };
 while(!gps_set_sucess)
 {
 sendUBX(setdm6, sizeof(setdm6)/sizeof(uint8_t));
 gps_set_sucess=getUBX_ACK(setdm6);
 }
}
void sendUBX(uint8_t *MSG, uint8_t len) {
 Serial.flush();
 Serial.write(0xFF);
 _delay_ms(500);
 for(int i=0; i<len; i++) {
 Serial.write(MSG[i]);
 }
}
boolean getUBX_ACK(uint8_t *MSG) {
 uint8_t b;
 uint8_t ackByteID = 0;
 uint8_t ackPacket[10];
 unsigned long startTime = millis();

// Construct the expected ACK packet
 ackPacket[0] = 0xB5; // header
 ackPacket[1] = 0x62; // header
 ackPacket[2] = 0x05; // class
 ackPacket[3] = 0x01; // id
 ackPacket[4] = 0x02; // length
 ackPacket[5] = 0x00;
 ackPacket[6] = MSG[2]; // ACK class
 ackPacket[7] = MSG[3]; // ACK id
 ackPacket[8] = 0; // CK_A
 ackPacket[9] = 0; // CK_B

// Calculate the checksums
 for (uint8_t ubxi=2; ubxi<8; ubxi++) {
 ackPacket[8] = ackPacket[8] + ackPacket[ubxi];
 ackPacket[9] = ackPacket[9] + ackPacket[8];
 }

while (1) {

// Test for success
 if (ackByteID > 9) {
 // All packets in order!
 return true;
 }

// Timeout if no valid response in 3 seconds
 if (millis() - startTime > 3000) {
 return false;
 }

// Make sure data is available to read
 if (Serial.available()) {
 b = Serial.read();

// Check that bytes arrive in sequence as per expected ACK packet
 if (b == ackPacket[ackByteID]) {
 ackByteID++;
 }
 else {
 ackByteID = 0; // Reset and look again, invalid order
 }
 }
 }
}

So there you go that’s the module in Dynamic Model 6 – Airborne < 1g which is generally the one you want for High Altitude ballooning. If your application is rocketry there is mode 8 – Airborne < 4g. Its quite viable to drop back to mode 3 – Pedestrian when below 9km in altitude. The airborne modes have large positional deviation, whereas the pedestrian modes have small deviation. Airborne modes are still perfectly accurate enough to locate a payload.

Ok so what next ? You have a choice at this point you can write a parser to read NMEA GNGGA strings to obtain your location information, you can use a prebuilt library that does this such as TinyGPS or finally you can use the UBX protocol to poll the module for information. I’ll discuss using UBX in the next article.