George Stone: 2016

My family has a cabin in the remote upper peninsula of Michigan. There we have a solar array that keeps the various vehicles batteries charged over the winter. I wanted to track the battery status through the winter when no one is up there. However, there is no internet up that far, but there is cell phone reception. So the plan is to have a Seeeduino Stalker run up 24/7/365 off of a lipo battery. Every hour or so it will power up and push the state of charge of the battery bank and voltage of the solar panels to Thingspeak.

A few people have worked on this, but even less have published in detail how to do it for the rest of us. So I've been working on it for the last month or so. I now have the GPRS able to connect to thingspeak and push data manually. All I have to do it clean up the code and make it into a more power friendly version that will work year round.

Hardware:

SeeedStalker 3.0
GPRS Bee Rev. 4 (SIM900)
LiPo Battery

Steps:

Wake Seeedstalker from sleep
Power up GPRSBee
Pull data from sensors
Connect to wireless network
Connect to thingspeak
Push data to thingspeak

Hardware Modifications:

It is necessary to solder P3 and P4 for for the RTC interrupts to function correctly. See the Seeeduino Stalker wiki for more details on this.

You will also need to solder a wire from pin 9 on the Bee socket to D5. See why here:
http://old.gprsbee.com/
Finally, for debugging, I find it's essential to have serial communication with my computer, so I've had to switch to using SW serial on D6 & D7. This means dealing with the Seeeduino Stalker v3.0's hardware bug. I found Seeed's wiki does not completely address the hardware bug. I had to cut a trace on P6 in addition to the one for P7. If you're having a hard time, just use a multi-meter to ensure you are wired how you expect to be.

Code:

1) Wake Seeedstalker from sleep -

This code has been written mostly by SeeedStudio on their wiki:
http://www.seeedstudio.com/wiki/Seeeduino-Stalker_v3#Data_Logger_Example
I'm not going to cover it again.

2) Power up GPRSBee - I will be adding this gradually in the coming weeks.

void gprspwr_on()
{
Serial.println("Turning on GPRS");
pinMode(5, OUTPUT);
digitalWrite(5,LOW);
delay(1000);
digitalWrite(5,HIGH);
delay(2000);
digitalWrite(5,LOW);
readATcommand("Call Ready",6,10000);
if (answer == 1){
Serial.println("GPRSbee is on!");
}
}

void gprspwr_off()
{
Serial.println("Turning off GPRS");
pinMode(5, OUTPUT);
digitalWrite(5,LOW);
delay(1000);
digitalWrite(5,HIGH);
delay(2000);
digitalWrite(5,LOW);
answer = readATcommand("NORMAL POWER DOWN",2,2000);
if (answer == 1){
Serial.println("Sucessful Powerdown Complete");
}
}

boolean gprspwr_status()
{
Serial.println("GPRS Power Status");
answer = sendATcommand("AT", "OK", 2, 2000);
if (answer == 0){
Serial.println("GPRSbee is Powered off!");
}
else if (answer == 1){
Serial.println("GPRSbee is on!");
}
return answer;
}

int8_t readATcommand(char* expected_answer1, unsigned int expected_answers, unsigned int timeout)
{

uint8_t x=0, answer=0;
boolean complete = 0;
char a;
char response[100];
unsigned long previous;
String incomingdata;
boolean first;

previous = millis();

for(int i = 0; i < expected_answers; i++){
x = 0;
complete = 0;
a = 0;
first = 0;
memset(response, '\0', 100); // Initialize the string
do{
if(SIM900.available() != 0){
a = SIM900.read();
//Serial.println(a,DEC);
if (a == 13){
a = SIM900.read();
//Serial.println(a,DEC);
if (a == 10){
if (first == 0){
//keep going, just ignore it
}
else{
Serial.print("string: #");
Serial.print(response);
Serial.println("#");
complete = 1;
}
}
}
else if(a == 0){
Serial.println("Found a blank");
}
else {
response[x] = a;
x++;
first = 1;
//Serial.println(response);
}
if(strstr(response, expected_answer1) != NULL)
{
answer = 1;
complete = 1;
Serial.print("string: #");
Serial.print(response);
Serial.println("#");
return answer;
}
else if(strstr(response, "ERROR") != NULL)
{
answer = 2;
}
}
}
while((complete == 0) && ((millis() - previous) < timeout));
//Serial.println(i);

}

return answer;
}

3) Pull data from sensors - This is dependent on your application, so I'm not going to cover it.

4) Connect to wireless network & thingspeak - I will be adding this gradually in the coming weeks.

void loop() {
if (SIM900.available())
{
Serial.write(SIM900.read());
}
//power up gprs
gprspwr_on();

//connect gprs to internet
answer = sendATcommand("AT+CGATT?","OK",5,2000);
answer = sendATcommand("AT+CSTT=\"CMNET\"","OK",3,2000);
answer = sendATcommand("AT+CIICR","OK",3,2000);
answer = sendATcommand("AT+CIFSR","OK",3,2000);
answer = sendATcommand("AT+CIPSPRT=0","OK",3,2000);

//connect gprs to thingspeak
answer = sendATcommand("AT+CIPSTART=\"tcp\",\"api.thingspeak.com\",\"80\"","CONNECT OK",5,2000);

//post data to thingspeak
answer = senddata(battery_percent());

delay(5000);

//power down gprs
gprspwr_off();

//put arduino to sleep?
for (int i=0; i<60; i++){
delay(1000);
Serial.println(i);
}
}

int8_t sendATcommand(char* ATcommand, char* expected_answer1, unsigned int expected_answers, unsigned int timeout)
{

uint8_t x=0, answer=0;
boolean complete = 0, first = 0;
char a;
char response[100];
unsigned long previous;
String incomingdata;

delay(100);
//Serial.println("Send AT Command");
while( SIM900.available() > 0) SIM900.read(); // Clean the input buffer
SIM900.println(ATcommand); // Send the AT command
Serial.println(ATcommand);
//Serial.println("AT Command Sent!");

previous = millis();

for(int i = 0; i < expected_answers; i++){
x = 0;
complete = 0;
a = 0;
first = 0;
memset(response, '\0', 100); // Initialize the string
do{
if(SIM900.available() != 0){
a = SIM900.read();
//Serial.println(a);
//Serial.println(a,DEC);
if (a == 13){
a = SIM900.read();
//Serial.println(a,DEC);
if (a == 10){
if (first == 0){
//keep going, just ignore it
}
else{
Serial.print("string: #");
Serial.print(response);
Serial.println("#");
complete = 1;
}
}
}
else if(a == 0){
Serial.println("Found a blank");
}
else {
response[x] = a;
x++;
first = 1;
//Serial.println(response);
}
if (strstr(response, expected_answer1) != NULL)
{
answer = 1;
complete = 1;
Serial.print("string: #");
Serial.print(response);
Serial.println("#");
}
else if(strstr(response, "ERROR") != NULL)
{
answer = 2;
complete = 1;
}
}
}
while((complete == 0) && ((millis() - previous) < timeout));

}
return answer;
}

5) Push data to thingspeak - I will be adding this gradually in the coming weeks.

int8_t senddata(float data){

Serial.print("Battery Percent = ");
Serial.println(data);

//while( SIM900.available() > 0) Serial.write(SIM900.read()); // Clean the input buffer
SIM900.println("AT+CIPSEND");
//Serial.println("AT+CIPSEND");
while( SIM900.available() > 0) Serial.write(SIM900.read()); // Clean the input buffer
delay(500);
SIM900.println("POST /update HTTP/1.1"); // Send the AT command
//Serial.println("POST /update HTTP/1.1");
while( SIM900.available() > 0) Serial.write(SIM900.read()); // Clean the input buffer
delay(500);
SIM900.println("Host: api.thingspeak.com"); // Send the AT command
//Serial.println("Host: api.thingspeak.com");
while( SIM900.available() > 0) Serial.write(SIM900.read()); // Clean the input buffer
delay(500);
SIM900.println("Connection: close"); // Send the AT command
//Serial.println("Connection: close");
while( SIM900.available() > 0) Serial.write(SIM900.read()); // Clean the input buffer
delay(500);
SIM900.println("X-THINGSPEAKAPIKEY: J79IQXQ0EOM6NCZX"); // Send the AT command
//Serial.println("X-THINGSPEAKAPIKEY: J79IQXQ0EOM6NCZX");
while( SIM900.available() > 0) Serial.write(SIM900.read()); // Clean the input buffer
delay(500);
SIM900.println("Content-Type: application/x-www-form-urlencoded"); // Send the AT command
//Serial.println("Content-Type: application/x-www-form-urlencoded");
while( SIM900.available() > 0) Serial.write(SIM900.read()); // Clean the input buffer
delay(500);
SIM900.println("Content-Length:12"); // Send the AT command
//Serial.println("Content-Length:12");
while( SIM900.available() > 0) Serial.write(SIM900.read()); // Clean the input buffer
delay(500);
SIM900.println(""); // Send the AT command
//Serial.println("");
while( SIM900.available() > 0) Serial.write(SIM900.read()); // Clean the input buffer
delay(500);
SIM900.print("field1="); // Send the AT command
SIM900.println(data);
while( SIM900.available() > 0) Serial.write(SIM900.read()); // Clean the input buffer
delay(500);
SIM900.println((char)26);
delay(500);
while( SIM900.available() > 0) Serial.write(SIM900.read()); // Clean the input buffer
delay(500);

answer = 0;
return answer;
}