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PostPosted: Thu Dec 28, 2017 1:36 am 

Joined: Thu Dec 28, 2017 12:02 am
Posts: 1
Hello guys, first post in Smwebhead, please be kind. If there were mistake in my topic, I'm so sorry, thank your time. Recently, me and my friends are building a boat which needs to steer towards certain coordinates. We have a GPS and a compass on board. We have written code which calculates the direction that the boat has to steer.

When we plug in our GPS100 together with the compass, the system works. When we add the servo to the circuit, the servo will swing back and forth continuously (even when in the code we only attach the servo and don't control it). If we unplug the GPS, the servo will stop swinging.

Why don't the GPS and servo function well in the sameArduino circuit?

Edit: Sorry guys, for not being specific enough. Let me give it another try:

I made a little diagram of the circuit we built:
I guess the code we made is too long to show up here (more than 300 lines of code), so I only took out the gps part of the code (wich happens to be most of the code).

#include <SoftwareSerial.h>
#include <Servo.h>
#include <TinyGPS.h>

TinyGPS gps;
SoftwareSerial ss(1,0);

static void smartdelay(unsigned long ms);
static void print_float(float val, float invalid, int len, int prec);
static void print_int(unsigned long val, unsigned long invalid, int len);
static void print_date(TinyGPS &gps);
static void print_str(const char *str, int len);

void setup()

Serial.print("Testing TinyGPS library v. "); Serial.println(TinyGPS::library_version());
Serial.println("by Mikal Hart");
Serial.println("Sats HDOP Latitude Longitude Fix Date Time Date Alt Course Speed Card Distance Course Card Chars Sentences Checksum");
Serial.println(" (deg) (deg) Age Age (m) --- from GPS ---- ---- to London ---- RX RX Fail");



void loop()
float flat, flon;
unsigned long age, date, time, chars = 0;
unsigned short sentences = 0, failed = 0;
static const double LONDON_LAT = 51.508131, LONDON_LON = -0.128002;

print_int(gps.satellites(), TinyGPS::GPS_INVALID_SATELLITES, 5);
print_int(gps.hdop(), TinyGPS::GPS_INVALID_HDOP, 5);
gps.f_get_position(&flat, &flon, &age);
print_float(flat, TinyGPS::GPS_INVALID_F_ANGLE, 10, 6);
print_float(flon, TinyGPS::GPS_INVALID_F_ANGLE, 11, 6);
print_int(age, TinyGPS::GPS_INVALID_AGE, 5);
print_float(gps.f_altitude(), TinyGPS::GPS_INVALID_F_ALTITUDE, 7, 2);
print_float(gps.f_course(), TinyGPS::GPS_INVALID_F_ANGLE, 7, 2);
print_float(gps.f_speed_kmph(), TinyGPS::GPS_INVALID_F_SPEED, 6, 2);
print_str(gps.f_course() == TinyGPS::GPS_INVALID_F_ANGLE ? "*** " : TinyGPS::cardinal(gps.f_course()), 6);
print_int(flat == TinyGPS::GPS_INVALID_F_ANGLE ? 0xFFFFFFFF : (unsigned long)TinyGPS::distance_between(flat, flon, LONDON_LAT, LONDON_LON) / 1000, 0xFFFFFFFF, 9);
print_float(flat == TinyGPS::GPS_INVALID_F_ANGLE ? TinyGPS::GPS_INVALID_F_ANGLE : TinyGPS::course_to(flat, flon, LONDON_LAT, LONDON_LON), TinyGPS::GPS_INVALID_F_ANGLE, 7, 2);
print_str(flat == TinyGPS::GPS_INVALID_F_ANGLE ? "*** " : TinyGPS::cardinal(TinyGPS::course_to(flat, flon, LONDON_LAT, LONDON_LON)), 6);

gps.stats(&chars, &sentences, &failed);
print_int(chars, 0xFFFFFFFF, 6);
print_int(sentences, 0xFFFFFFFF, 10);
print_int(failed, 0xFFFFFFFF, 9);



static void smartdelay(unsigned long ms)
unsigned long start = millis();
while (ss.available())
} while (millis() - start < ms);

static void print_float(float val, float invalid, int len, int prec)
if (val == invalid)
while (len-- > 1)
Serial.print(' ');
Serial.print(val, prec);
int vi = abs((int)val);
int flen = prec + (val < 0.0 ? 2 : 1); // . and -
flen += vi >= 1000 ? 4 : vi >= 100 ? 3 : vi >= 10 ? 2 : 1;
for (int i=flen; i<len; ++i)
Serial.print(' ');

static void print_int(unsigned long val, unsigned long invalid, int len)
char sz[32];
if (val == invalid)
strcpy(sz, "*******");
sprintf(sz, "%ld", val);
sz[len] = 0;
for (int i=strlen(sz); i<len; ++i)
sz[i] = ' ';
if (len > 0)
sz[len-1] = ' ';

static void print_date(TinyGPS &gps)
int year;
byte month, day, hour, minute, second, hundredths;
unsigned long age;
gps.crack_datetime(&year, &month, &day, &hour, &minute, &second, &hundredths, &age);
if (age == TinyGPS::GPS_INVALID_AGE)
Serial.print("********** ******** ");
char sz[32];
sprintf(sz, "%02d/%02d/%02d %02d:%02d:%02d ",
month, day, year, hour, minute, second);
print_int(age, TinyGPS::GPS_INVALID_AGE, 5);

static void print_str(const char *str, int len)
int slen = strlen(str);
for (int i=0; i<len; ++i)
Serial.print(i<slen ? str[i] : ' ');

PostPosted: Thu Dec 28, 2017 5:35 pm 
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Joined: Sun Jul 22, 2012 6:10 pm
Posts: 2027
Location: West Palm Beach, FL
This is a little off topic for this forum, but there are a couple of
electronics guys here. Is this for a model boat?

I don't have time to study all the code, but looking at the diagram, it
looks like you are using DIO pin 3 (a PWM capable pin) to go to the
digital TX on the GPS. Perhaps you could switch that to one of the
non PWM pins (like DIO #2) to make sure it is not interfering with
the PWM going to servo (DIO #5). Other than that, check that you
have good vcc and gnd connections going through your breadboard.

"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings

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