This post further discusses on extracting commands sent to an Arduino in form of an SMS, using SIM800 module. Discussed setup can be used as a backup route to an IoT device, enabling access in case of a failure in the primary network connectivity.
A backup route to be used in case your internet connections went down or maybe “the thief” took down the router first, leaving no way for you to connect with your master mind IoT security system. (wink)
This is the continuation of a previous post titled “Quickstart SIM800 (SIM800L) with Arduino“, which is recommended for anyone new to SIM800.
Reading Incoming SMS
Looking an AT command manual for SIM800 we found in the previous post it is clear that “ AT+CMGL “REC UNREAD” 0 ” can be used to list all the unread SMS messages. Using the index obtained by “CMGL”, it is possible to use “AT+CMGR <index> 0” to read contents of each unread message. But with this approach, it is necessary to pull messages stored in SIM periodically. This can be very inefficient in case of a system that does not get commands very frequently. If Arduino is running off of a battery above check will drain the battery pretty fast. Moreover, commands sent will not apply immediately.
Due to above limitations and inefficiencies, it is best to use “AT+CNMI” command (“New SMS Message Indications”) to get notified of any new incoming SMS message. Trying “AT+CNMI 1,2,0,0,0” on Arduino IDE “Serial Monitor” results in below, upon SMS arrival :
Enhanced Sample
With below code it is possible to process incoming “New SMS Message Indications” in form of “+CMT”, check the next line for the actual message content and do a certain action based on the command received. For simplicity, below code will only turn ON and OFF the LED built into Arduino (digital pin 13).
It is obvious that same logic can be applied even to operate an A/C powered device (using a relay).
Below sample is available for download at : https://www.ayomaonline.com/?download=SIM800SMS
#include <gprs.h>
#include <softwareserial.h>
#define TIMEOUT 5000
#define LED_PIN 13
bool ledStatus;
GPRS gprs;
void setup() {
Serial.begin(9600);
while(!Serial);
Serial.println("Starting SIM800 SMS Command Processor");
gprs.preInit();
delay(1000);
while(0 != gprs.init()) {
delay(1000);
Serial.print("init error\r\n");
}
//Set SMS mode to ASCII
if(0 != gprs.sendCmdAndWaitForResp("AT+CMGF=1\r\n", "OK", TIMEOUT)) {
ERROR("ERROR:CNMI");
return;
}
//Start listening to New SMS Message Indications
if(0 != gprs.sendCmdAndWaitForResp("AT+CNMI=1,2,0,0,0\r\n", "OK", TIMEOUT)) {
ERROR("ERROR:CNMI");
return;
}
Serial.println("Init success");
}
//Variable to hold last line of serial output from SIM800
char currentLine[500] = "";
int currentLineIndex = 0;
//Boolean to be set to true if message notificaion was found and next
//line of serial output is the actual SMS message content
bool nextLineIsMessage = false;
void loop() {
//Write current status to LED pin
digitalWrite(LED_PIN, ledStatus);
//If there is serial output from SIM800
if(gprs.serialSIM800.available()){
char lastCharRead = gprs.serialSIM800.read();
//Read each character from serial output until \r or \n is reached (which denotes end of line)
if(lastCharRead == '\r' || lastCharRead == '\n'){
String lastLine = String(currentLine);
//If last line read +CMT, New SMS Message Indications was received.
//Hence, next line is the message content.
if(lastLine.startsWith("+CMT:")){
Serial.println(lastLine);
nextLineIsMessage = true;
} else if (lastLine.length() > 0) {
if(nextLineIsMessage) {
Serial.println(lastLine);
//Read message content and set status according to SMS content
if(lastLine.indexOf("LED ON") >= 0){
ledStatus = 1;
} else if(lastLine.indexOf("LED OFF") >= 0) {
ledStatus = 0;
}
nextLineIsMessage = false;
}
}
//Clear char array for next line of read
for( int i = 0; i < sizeof(currentLine); ++i ) {
currentLine[i] = (char)0;
}
currentLineIndex = 0;
} else {
currentLine[currentLineIndex++] = lastCharRead;
}
}
}
Turning LED ON :
Turning LED OFF :
Related Posts
November 28, 2015 GY-GPS6MV2 – NEO6MV2 (Neo 6M) GPS Module with Arduino / USB TTL (14)
November 25, 2015 Quickstart SIM800 (SIM800L) with Arduino (183)
May 22, 2016 Analyzing Network Traffic with OpenWrt (5)
November 29, 2015 DIY 3D printer – Building RepRap Prusa i3 in Sri Lanka (work in progress) (3)
December 19, 2017 Using Raspberry Pi to Program BLE400 / NRF51822 (0)
hi, I’m having a problem with $gt; and <, it says “‘gt’ was not declared in this scope” when I try to upload the code, do you know what could be the problem?
Hi RAF,
If I understood your problem properly, your browser might have copied the code with the HTML encoding. Can you replace all “>” with “>” signs and “<” with “<" signs. Maybe there are other encoded items as well. Let me know if you find other errors. If so, I will provide a text file with code for you to download. Regards, Ayoma
After replace all “>” with “>” signs and “<” with “<" signs
is it exit for verify the sketch from row 83 to row 88
exit status 1 row83
expected ')' before ';' token
84: error: 'i' was not declared in this scope
90: error: expected declaration before '}' token
exit status 1
expected unqualified-id before 'else'
can you please load up the working code ,
Thank you anyway for your simm800 post's
/Stefan
Looks like I’ll have to change the syntax highlighter soon 🙂 I have corrected the post and added additional download link for the code. Please note that this is continuation of “Quickstart SIM800 (SIM800L) with Arduino” (linked on top of the post). You will need Seeeduino_GPRS library (https://github.com/Seeed-Studio/Seeeduino_GPRS) to get this working. Read through the first post for relevant details.
SIM800 moduel showing power check failed! error after “Starting SIM….”
Hi rx and tx pins are connected to what I base ?
where can i get the gprs.h???
hello sir,
Thank your sir for the code, the code provided by you is working …sir i have a question assume i have two numbers (number1 & number 2) if i send command from number1 the led should on..but if i send LED ON command from number2 the led should not on …then how could we edit the code to worked like that?
please reply soon..
thanks for your codes.
to delete the all sms i used below codes
//if(0 != gprs.sendCmdAndWaitForResp(“AT+CMGD=1,4\r\n”, “OK”, TIMEOUT))
//{Serial.println(“SMS was deleted”);}
//else
// {Serial.println(“SMS was not deleted”);}
but it was not work out.
what is the problem behind that.
thanks
Oh finally AT+CMGDA=1 was work out with below codes
if(0 != gprs.sendCmdAndWaitForResp(“AT+CMGDA=1\r\n”, “OK”, 5))
{Serial.println(“SMS was deleted”);}
else
{Serial.println(“SMS was not deleted”);}
it takes some times to delete sms, so then set timeout=5 //timerEnd – timerStart > 1000 * timeout
Hi. Ayoma
I used your code on Arduino ouno and all things is right just when I send on or off led, no action will happen and led not turns on.
Pleas help me.
add pin configuration line as describe below:
GPRS gprs;
void setup() {
//setup pin 13
pinMode(13, OUTPUT);
need to change this section:
//Read message content and set status according to SMS content
if (lastLine.indexOf( “LED ON”) >= 0) {
//ledStatus = 1;
digitalWrite(LED_PIN, HIGH);
Serial.println(“ON”);
} else if (lastLine.indexOf( “LED OFF”) >= 0) {
//ledStatus = 0;
digitalWrite(LED_PIN, LOW);
Serial.println(“OFF”);
}
i want to controlle more leds so your change can help me or not ?
HI .i am also facing same problem,i am using arduino uno r3.i changed the code as per below but ,i am not getting that.
it’s showing Starting SIM800 SMS Command Processor
Init success
when I send led on or led off , no action will happen and led not turns on.
please help me.
Hi, Im having trouble, it says gprs was not declared in this scope thank you
To wich pin of arduino shud i connect TX and RX pins of SIM800 module????Plz let us knw ur connection also..It wil be of great help
tx (9), rx (10)
try this if ur using uno
I have unreadable message:
+CMT: “+359xxxxxxxxxxxx”,””,”17/02/17,21:28:03+08″
Content: ….
004A006A006A006A006A006A
My message is Jjjjjj….
This is ASCII CIPHERTEX … but how can i convert it from ASCII CIPHERTEX to READABLE String … for example UTF-8
type AT+CMGF=1
which means show in text mode
you’re in PUD mode which is HEX code
hi, does this code work in arduino mega? i tried it with uno its work. but i have problem working it with mega.
HI,
is it possible change the rx and tx pins???
pleas help me its so necessary for me
hi thanks for your code ,
led was not on i tri
pinMode(13,OUTPUT):
led is on
Is there a way to only allow the program to run if a particular specified phone number is sending the sms?
Do not understand why (AT+CMGR=1 ) can drain the battery and (AT+CNMI) not.
In both cases, the SIM memory is readed and the power consumption is similar. But if AT+CNMI is used, the stored system configuracion has changing.
Ok after re-read the program now i understand, the script is listening the GSM port for intakes…
Nice.
hey sir I need your help. How to fix this kind of error? Thank you for your answer..
C:\Users\jmmwah\Documents\Arduino\GSM_GPRSLibrary_SMSas\GSM_GPRSLibrary_SMSas.ino: In function ‘void setup()’:
C:\Users\jmmwah\Documents\Arduino\GSM_GPRSLibrary_SMSas\GSM_GPRSLibrary_SMSas.ino:41:44: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]
if (sms.SendSMS(“095048”, “Arduino SMS”))
^
C:\Users\jmmwah\Documents\Arduino\GSM_GPRSLibrary_SMSas\GSM_GPRSLibrary_SMSas.ino:41:44: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]
me succedo lo stessa cosa ho provato prima con arduino uno e poi con arduino mega non vorrei che sia una impostazione del programma.
per caso hai trovato una soluzione???
where i can get gprs library file? can you send me the link please?
https://github.com/Seeed-Studio/Seeeduino_GPRS
Link to “Quickstart SIM800 (SIM800L) with Arduino” seems to reference an empty page…