Issues with using GPS & servo together

[system]

Nick,

Thanks for the interrupt explanation.

It's just Serial ... the basic serial examples show that. Use pins 0 and 1, and then do stuff like:

Serial.begin (GPSBAUD);

And then:

 // read gps
  while(Serial.available())
  {
      int c = Serial.read();

... and so on.

You've already got Serial.begin there. I don't know why as you don't seem to be using it. The hardware Serial is preferred to software Serial.

I gave this a try and while the servo works, I can no longer read the GPS.

// gps code adapted from http://www.sparkfun.com/tutorials/173
// servo code adapted from http://arduino.cc/it/Tutorial/Sweep

// boolean debug = true;

// setup gps
// #include <SoftwareSerial.h>
// SoftwareSerial uart_gps(RXPIN, TXPIN);

#include <TinyGPS.h>
#define RXPIN 2
#define TXPIN 3
#define GPSBAUD 4800
TinyGPS gps;

float latitude, longitude;

// setup steering servo
#include <Servo.h> 
Servo steeringServo;  // 1000 us < input < 2000 us

void setup() {
  Serial.begin(GPSBAUD);
    
  // start steering servo
  steeringServo.attach(8);
}

void loop() {
  // read gps
  while(Serial.available())
  {
      int c = Serial.read();
           
      if(gps.encode(c))
      {
        gps.f_get_position(&latitude, &longitude);
      }
  }
  
  // it takes 20 readings before latitude and longitude readings work
  Serial.print("Current Lat/Long: "); 
  Serial.print(latitude,6); 
  Serial.print(", "); 
  Serial.println(longitude,6);
  Serial.println("");
 
  // send steering angle
  steeringServo.writeMicroseconds(1500);
}

If that doesn't work (although I guess lots of people would be doing servos and serial) you could always use the hardware PWM pins and "manually" generate the correct length pulses. The hardware PWM can generate pulses without needing to use interrupts at all.

In my experience, in order for the servo to hold a particular angle, it needs to be constantly receiving a PWM signal. However, if I am manually generating the PWM signal, then any time the Arduino runs other code (e.g, updating the gps or running the obstacle avoidance algorithm), it stops sending the PWM signal. Is there a work around for this?

If I picked up a mega (http://arduino.cc/en/Main/ArduinoBoardMega2560), with multiple serial ports, perhaps the GPS and Servo wouldn't fight over one. I read about other folks having success with getting the Sparkfun GPS shield to work on the mega (Arduino Forum), but I don't understand how UNO shields can work on Megas--it seems like the board layouts are different. Are Uno shields compatible with Mega boards? Might a Mega solve my problem?