Serial communications questions

Hi all!

I have an adafruit fona 800 shield on an arduino uno and it’s working great, except for one problem…

My code is based off of the adafruit code for their product. Anyway, it sets up the fona to send a signal if a text message is recieved. The main loop looks for data from the fona, if there’s no data, it does things and starts the loop() again. Everything is working great, until I try to get the RSSI value. Once I do that, the next time thru the loop(), the fona won’t send a notification that it has received a SMS text message.

The best code example to show my problem is to use the adafruit SMS_response sketch, and add the code to get the RSSI value at the end of the loop. Without the rssi code, the sketch works fine, with it, the sketch never sees the incoming SMS.


Open up the serial console on the Arduino at 115200 baud to interact with FONA

This code will receive an SMS, identify the sender's phone number, and automatically send a response


#include "Adafruit_FONA.h"

#define FONA_RX 2
#define FONA_TX 3
#define FONA_RST 4

// this is a large buffer for replies
char replybuffer[255];

// We default to using software serial. If you want to use hardware serial
// (because softserial isnt supported) comment out the following three lines 
// and uncomment the HardwareSerial line
#include <SoftwareSerial.h>
SoftwareSerial fonaSS = SoftwareSerial(FONA_TX, FONA_RX);
SoftwareSerial *fonaSerial = &fonaSS;

// Hardware serial is also possible!
//  HardwareSerial *fonaSerial = &Serial1;

// Use this for FONA 800 and 808s
Adafruit_FONA fona = Adafruit_FONA(FONA_RST);
// Use this one for FONA 3G
//Adafruit_FONA_3G fona = Adafruit_FONA_3G(FONA_RST);

uint8_t readline(char *buff, uint8_t maxbuff, uint16_t timeout = 0);

void setup() {
  while (!Serial);

  Serial.println(F("FONA SMS caller ID test"));
  Serial.println(F("Initializing....(May take 3 seconds)"));

  // make it slow so its easy to read!
  if (! fona.begin(*fonaSerial)) {
    Serial.println(F("Couldn't find FONA"));
  Serial.println(F("FONA is OK"));

  // Print SIM card IMEI number.
  char imei[16] = {0}; // MUST use a 16 character buffer for IMEI!
  uint8_t imeiLen = fona.getIMEI(imei);
  if (imeiLen > 0) {
    Serial.print("SIM card IMEI: "); Serial.println(imei);

  fonaSerial->print("AT+CNMI=2,1\r\n");  //set up the FONA to send a +CMTI notification when an SMS is received

  Serial.println("FONA Ready");

char fonaNotificationBuffer[64];          //for notifications from the FONA
char smsBuffer[250];

void loop() {
  char* bufPtr = fonaNotificationBuffer;    //handy buffer pointer
  if (fona.available())      //any data available from the FONA?
    int slot = 0;            //this will be the slot number of the SMS
    int charCount = 0;
    //Read the notification into fonaInBuffer
    do  {
      *bufPtr =;
    } while ((*bufPtr++ != '\n') && (fona.available()) && (++charCount < (sizeof(fonaNotificationBuffer)-1)));
    //Add a terminal NULL to the notification string
    *bufPtr = 0;

    //Scan the notification string for an SMS received notification.
    //  If it's an SMS message, we'll get the slot number in 'slot'
    if (1 == sscanf(fonaNotificationBuffer, "+CMTI: " FONA_PREF_SMS_STORAGE ",%d", &slot)) {
      Serial.print("slot: "); Serial.println(slot);
      char callerIDbuffer[32];  //we'll store the SMS sender number in here
      // Retrieve SMS sender address/phone number.
      if (! fona.getSMSSender(slot, callerIDbuffer, 31)) {
        Serial.println("Didn't find SMS message in slot!");
      Serial.print(F("FROM: ")); Serial.println(callerIDbuffer);

        // Retrieve SMS value.
        uint16_t smslen;
        if (fona.readSMS(slot, smsBuffer, 250, &smslen)) { // pass in buffer and max len!

      //Send back an automatic response
      Serial.println("Sending reponse...");
      if (!fona.sendSMS(callerIDbuffer, "Hey, I got your text!")) {
      } else {
      // delete the original msg after it is processed
      //   otherwise, we will fill up all the slots
      //   and then we won't be able to receive SMS anymore
      if (fona.deleteSMS(slot)) {
      } else {
        Serial.print(F("Couldn't delete SMS in slot ")); Serial.println(slot);
  // read the RSSI
  uint8_t n = fona.getRSSI();
  int8_t r;
  Serial.print(F("RSSI = ")); Serial.print(n); Serial.print(": ");
  if (n == 0) r = -115;
  if (n == 1) r = -111;
  if (n == 31) r = -52;
  if ((n >= 2) && (n <= 30)) {
    r = map(n, 2, 30, -110, -54);
  Serial.print(r); Serial.println(F(" dBm"));

  delay (5000);
  fonaSerial->print("AT+CNMI=2,1\r\n");  //set up the FONA to send a +CMTI notification when an SMS is received

If there is any more info needed, just ask. I am thankful to any help!


Hi all!

I have an adafruit fona gsm shield on an arduino uno and the two communicate via software serial. The arduino serial is set to 115200 baud and the serial monitor is also set to the same. I'm getting all my Serial.print() on the serial monitor, as expected. At the same time, I appear to be getting all the serial communication between the fona and the arduino in the serial monitor as well. The software serial fona baud rate it set to 4800, but yet I am seeing the AT command comunication between the two.

Is there anyway to filter what is displayed in the serial monitor? So I would only be seeing what I am printing to the serial?

This is in effort to figure out this problem:

And my code can be found there. I can paste the code here if needed, but I don't think it's needed...


Why did you start a second topic about the same program ?

Topics merged

they are not the same topic, same subject, yes, different topics.

The topic of the post in the project guidance section is why I am not getting data from the fona.

The topic of the post in the programming sections is how to quiet out some of the serial data sent by the arduino to the serial monitor. Yes, it is data from the fona, part of the other problem, but not about the other problem at all.....

I only included the link for informational purposes...


Sorry, but I still think that the topics belong together. You can change the topic title if you like and the topic can be moved to whatever forum section you like

In my experience the Programming section gets the most traffic and is seen by the most people