As goats are naturally born masters of escaping, we soon realized that the electric fence only should be considered as the first line of defense. Usually, the most clever ones finds their way out, and then calls for the others to follow, and generally, their just heading out to a nearby pasture, where the grass is allegedly greener, or home to the barn. On a few occasions though, they have been spooked by wild boars, and ran off into the forest. When I was tracking them out on a small dirt road, and a neighbor called from his forestry tractor, about 3 km out, and asked if maybe my goats where out hiking, I realized that we have a need for a tracking device. The idea of the GoTo Goat device was born, a GPS-module, transmitting coordinates over the cell network.

Features:

Real-time GPS location

Upload coordinates to a cloud service, or your own server over GPRS

Solar powered

Android locator app

Component list

Microcontroller: Arduino nano 6 euro

GPRS module: SIM800L 5 euro

GPS module: Ublox NEO-6M 7 euro

Power supply: Linocell 3X Solar Powerbank 8000 mAh 50 euro

Step-down regulator: AMS1117 adjustable (5V-3.7V) 1 euro

Sim card (Telia) free

Total cost: 19 euro for the components and 50 for the powerbank, but i bought the powerbank locally in Sweden, and there are much cheaper ones around on ebay. With a little more labour put into sourcing, the cost could probably drop to about 30 euro.

The SIM800L

This is a very nice little module. Essentially a complete cell phone, except for user interface, speaker and mic. It’s controlled from the arduino by sending AT commands through serial communication. The SIM800L is supposed to be powered by a 3.7V Li cell, as in a cellphone, and that’s why the buck converter is needed in this setup to bring the current down from 5V.

The only functionality used here is the GPRS device for sending over HTTP, but using SMS or DMTF for controlling the unit are possibilities as well as calling the goat for an occasional chat.

The NEO-6M

A neat GPS-module supported by the arduino TinyGPS library. Pretty fast on getting a fix, and supplying coordinates once a second.

The Nano

I choose an Arduino nano for prototyping, since it has it’s own FTDI, a reasonable size and a friendly number of pins. If the size, power consumption and prize needs to be further tweaked, I can’t see any reason not to use a mini pro though. The SIM800L is rated for max 3.7V to 4.1V so the internal voltage regulators will be useless.

 The SIM

Any sim card that supports GPRS will work, but it’s recommended to use one that not expires too soon after charging. As very little traffic volumes are transmitted, it would be a shame if the card needed to be refueled every 3 months or so. Instead, if you can find one that works for several years, and only using the throttled speed when paid data is depleted, that would be completely sufficient.

Connections

Cloud API

I choose thingspeak.com as cloud service to store the coordinates. Mostly because I already use it for other sensors, so I’m already familiar with the API. Virtually any online API would be suitable, as long as you can send in values through a HTTP GET parameter.

Thingspeak will let you send in 3 000 000 updates / year with their free account, so that will limit you to 5.7 updates / minute. I’ll go for max 1/min, probably less. Since you are putting the API key in the arduino code, you don’t want to use a service that is likely to go off the market, or become ”premium only”, like Xively did. To be sure that the service stays alive, you could host your own thingspeak platform on a raspberry pi or similar.

Code

The NEO-6M is very simple to interface from the Arduino. I used the kitchensink example from the TinyGPS library, and trimmed it down to the bare necessities.

The SIM800L is more complicated to interface, since you need 2-way communication to ensure that the commands have been successfully performed. I found some example code at Cassiopeia that was very helpful. Even if I do not use DMTF functionality as in the example, their approach for communicating with the SIM800L is very convenient.

As both the NEO-6M, the SIM800L and the arduino IDE Serial monitor are using serial communication for interfacing the arduino, there will be issues regarding which ports to use. I kept the hardware serial (Serial) for debugging purposes, and let only the computer interface with it. For the modules, I assigned two SoftwareSerial ports, sim800 on pin 7 and 8 and ss on pin 3 and 4. To keep the communication channels separated, the arduino is instructed on which one to listen, depending on where input is expected.

#include <SoftwareSerial.h>
#include <TinyGPS++.h>
#include <avr/sleep.h>
#include <avr/wdt.h>
//Thingspeak channel
#define CHANNEL 199082 //Not used
//Thingspeak API write key
#define APIKEY "XXXXXXXXX"//Put your own write key here
//SIM800 TX is connected to Arduino D8
#define SIM800_TX_PIN 8
#define RATE 10000 //GPS sampling rate
//SIM800 RX is connected to Arduino D7
#define SIM800_RX_PIN 7
static const int RXPin = 3, TXPin = 4;
static const uint32_t GPSBaud = 9600;
const int sim_rst = 5;
int errors = 0;
//Create software serial object to communicate with SIM800
SoftwareSerial sim800(SIM800_TX_PIN,SIM800_RX_PIN);
SoftwareSerial ss(RXPin, TXPin);
TinyGPSPlus gps;
unsigned long last = 0UL;
// watchdog interrupt
ISR(WDT_vect)
{
wdt_disable(); // disable watchdog
}
void myWatchdogEnable(const byte interval)
{
MCUSR = 0; // reset various flags
WDTCSR |= 0b00011000; // see docs, set WDCE, WDE
WDTCSR = 0b01000000 | interval; // set WDIE, and appropriate delay

wdt_reset();
set_sleep_mode (SLEEP_MODE_PWR_DOWN);
sleep_mode(); // now goes to Sleep and waits for the interrupt
}
void setup() {
//Begin serial comunication with Arduino and Arduino IDE (Serial Monitor)
Serial.begin(9600);
while(!Serial);

//Beging serial communication with Arduino and SIM800
sim800.begin(9600);
delay(1000);
ss.begin(GPSBaud);
delay(1000);
Serial.println("Setup Complete!");
last = millis()-RATE;
}

void loop() {
errors = 0;
// Dispatch incoming characters from GPS
ss.listen();
while (ss.available() > 0)
gps.encode(ss.read());
if (millis() - last > RATE)
{
if (gps.location.isValid())
{
static const double OFFICE_LAT = 56.000, OFFICE_LON = 14.000; //Hard coded reference coordinates if needed in the future
double distanceToOffice =
TinyGPSPlus::distanceBetween(
gps.location.lat(),
gps.location.lng(),
OFFICE_LAT,
OFFICE_LON);
Serial.println(distanceToOffice);
double courseToOffice =
TinyGPSPlus::courseTo(
gps.location.lat(),
gps.location.lng(),
OFFICE_LAT,
OFFICE_LON);
char tmpCourse[10];
char tmpDistance[10];
char tmpLat[10];
char tmpLng[10];
char tmpSpeed[10];
char params[200];
int batteryLevel;
//Convert GPS data to strings
dtostrf(gps.location.lat(),1,6, tmpLat);
dtostrf(gps.location.lng(),1,6, tmpLng);
dtostrf(distanceToOffice/1000, 1,6, tmpDistance);
dtostrf(courseToOffice,1,6, tmpCourse);
dtostrf(gps.speed.kmph(), 1,6, tmpSpeed);
sim800.listen();//Turn to sim800l channel
disconnectGPRS();//Sometimes, the sim800l gets stuck with GPRS activated, and trying to activate it again will naturally fail.
while(!wakeUpSim800());
if(simOK()){
batteryLevel= getBatteryLevel();
Serial.print("Battery level: ");
Serial.println(batteryLevel);
sprintf(params, "apikey=%s&field1=%s&field2=%s&field3=%s&field6=%d", APIKEY, tmpLat, tmpLng, tmpSpeed, batteryLevel);
Serial.println(params);
//Next three stages are sequential. Error handling means that if the sequence is not completed with less than 5 unsuccessful tries on all stages, there is something wrong, and the sequence is aborted.
while(!initGPRS()&&errors++<5);

while(!initHTTP()&&errors++<5);

while(!putDataToThingspeak(params)&&errors++<5);
errors = 0;
while(!disconnectGPRS()&&errors++<5);
while(!powerDownSim800());
delay(200);
Serial.println("Entering watchdog sleep");
delay(100);
myWatchdogEnable (0b100001); // 8 seconds
myWatchdogEnable (0b100001); // 8 seconds
myWatchdogEnable (0b100001); // 8 seconds
myWatchdogEnable (0b100001); // 8 seconds
myWatchdogEnable (0b100001); // 8 seconds
myWatchdogEnable (0b100001); // 8 seconds
myWatchdogEnable (0b100001); // 8 seconds
myWatchdogEnable (0b100001); // 8 seconds

Serial.println("Resuming operations");
}
ss.listen(); //Turn back to GPS channel
}

if (gps.charsProcessed() < 10)
Serial.println(F("WARNING: No GPS data. Check wiring."));

last = millis();

}
}
boolean wakeUpSim800(){
Serial.println(F("Checking for sim800 module..."));

digitalWrite(sim_rst, LOW); // hardware reset after sleep RST
delay(300);
digitalWrite(sim_rst, HIGH);

// time to startup 3 sec
for (int i = 0; i < 6; i++) {
digitalWrite(13, HIGH); // green LED blink after RESET
delay(250);
digitalWrite(13, LOW);
delay(250);
}

sim800.println("AT"); // check if sim800 module responds
delay(100);
if (sim800.find("OK")) {
Serial.println(F("sim800 module awake"));
return true;
}
else{
Serial.println(F("sim800 module not found"));
return false;
}

}
boolean simOK() { // SIM CHECK OK
Serial.println(F("Checking for SIM card.. "));

sim800.println("AT"); // check if sim800 module responds
delay(100);
if (sim800.find("OK")) {
Serial.println(F("sim800 module found"));

delay(100); // wait for sim800 to settle a bit
sim800.println("AT+CFUN=1"); // operation
if (sim800.find("OK"))
Serial.println(F("Function level 1"));
else
return false;
delay(2000);
sim800.println("AT+CSMINS?"); // check if SIM card inserted
delay(100);
if (sim800.find("CSMINS: 0,0")) {
Serial.println(F("no SIM card found, stop here"));
return false;
}
Serial.println(F("SIM card found")); // continue if SIM card found

Serial.println(F("Allow some time for SIM to register on the network.."));
Serial.println();
delay(1000);
return true;
}
else{
Serial.println(F("sim800 module not found, stop here"));
return false;
}
}

void simReply() { // SIM REPLY
delay(500);
while (sim800.available()) {
char c = sim800.read();
if (c != '\n') Serial.write(c); // replace new line with space
else Serial.print(" ");
delay(5);
}
Serial.println();
}

boolean initGPRS(){
boolean noError = true;
sim800.println("AT+CIPSHUT"); //Ensure GPRS PDP is down before init
simReply();
//delay(1000);
sim800.println("AT+CGATT=1");//Attach to GPRS service
simReply();

sim800.println("AT+SAPBR=3,1,CONTYPE,GPRS");//Set(3) bearer connected(1) to Contype GPRS
if (sim800.find("ERROR"))
noError = false;
sim800.println("AT+CGATT=1");//Attach to GPRS service
if (sim800.find("ERROR"))
noError = false;
sim800.println("AT+SAPBR=3,1,APN,online.telia.se");//Set(3) bearer connected(1) to APN
if (sim800.find("ERROR"))
noError = false;
sim800.println("AT+SAPBR=1,1");//Open connected bearer
if (sim800.find("ERROR"))
noError = false;
Serial.print("initGPRS finished with no errors = ");
Serial.println(noError);
return noError;

}

boolean initHTTP(){
boolean noError = true;
sim800.println("AT+HTTPTERM");
if (sim800.find("ERROR"))
noError = false;
sim800.println("AT+HTTPINIT");
if (sim800.find("ERROR"))
noError = false;
sim800.println("AT+HTTPPARA=CID,1");
if (sim800.find("ERROR"))
noError = false;
Serial.print("initHTTP finished with no errors = ");
Serial.println(noError);
return noError;
}
boolean putDataToThingspeak(char params[200]){
boolean noError = true;
char req[250];
sprintf(req, "AT+HTTPPARA=URL,api.thingspeak.com/update?%s", params);
Serial.println(req);
sim800.println(req);
if (sim800.find("ERROR"))
noError = false;
delay(1000);
sim800.println("AT+HTTPACTION = 0");
if (sim800.find("ERROR"))
noError = false;
Serial.print("putDataToThingspeak finished with no errors = ");
Serial.println(noError);
return noError;
}

boolean disconnectGPRS(){
boolean noError = true;
sim800.println("AT+CIPSHUT");
if (sim800.find("ERROR"))
noError = false;
sim800.println("AT+SAPBR=0,1");
if (sim800.find("ERROR"))
noError = false;
sim800.println("AT+CGATT=0");
if (sim800.find("ERROR"))
noError = false;
sim800.println("AT+CFUN=0");
if (sim800.find("ERROR"))
noError = false;
Serial.print("disconnectGPRS finished with no errors = ");
Serial.println(noError);
return noError;

}
int getBatteryLevel(){
sim800.listen();
sim800.println("AT+CBC"); // battery level
delay(500);
String s = sim800.readStringUntil(',');//Grab the value between the commas
String level = sim800.readStringUntil(',');

return(level.toInt());
}

boolean powerDownSim800(){
boolean noError = true;
sim800.println("AT+CPOWD=1");
if (sim800.find("ERROR"))
noError = false;

Serial.print("SIM800l power down = ");
Serial.println(noError);
return noError;

}

Here are the latitude results from thingspeak, for more, go to the GoTo goat section on the IoT page.

Android app

The Android app is still just an embryo, but it will find a goat… You can find it on Play: https://play.google.com/apps/testing/com.framtidabruk.gotogoats

You need to enter your own thingspeak.com Api key and channel ID in the settings before it becomes useful.