GSM SIM900A MINI(v3.8.3) Connection problem

Other Hardware General Electronics
1

Hello, I am currently having trouble with my GSM SIM900A MINI with its connection. The connection LED of the sim module doesn't blink but it's always on and I have already connected it to an outer power source (2 3.7V Lithium ion batteries) while having common ground with my Arduino Nano 33 IoT. I have already searched youtube videos about it but their modules seem to have to problem with the connection and i can't figure out why my LED doesn't blink. Is there a way to resolve this problem? Thank you.

2

Hi there! A diagram would be very helpful to us.

3

Hello, here would be the picture of the circuit

482800846_2149722025483508_6658271795257360353_n
482800846_2149722025483508_6658271795257360353_n2048×1536 157 KB

And here would be the code that i used but it wouldn't send the text message or receive messages. I have also tried changing the baud rates but it's still the same


#include <Arduino.h>

void readGSMResponse() {
  unsigned long timeout = millis() + 2000;  // 2-second timeout
  while (millis() < timeout) {
    while (Serial1.available()) {
      char c = Serial1.read();
      Serial.write(c);
    }
  }
}

void setup() {
  Serial.begin(9600);
  while (!Serial);  
  Serial.println("Initializing GSM module...");

  Serial1.begin(9600);  
  delay(1000);  

  Serial1.println("AT");
  delay(500);
  readGSMResponse();

  Serial1.println("AT+CMGF=1");
  delay(500);
  readGSMResponse();

  Serial1.println("AT+CMGS=\"+639391803733\"");
  delay(500);
  readGSMResponse();

  Serial1.print("Hello, this is a test SMS from Arduino Nano 33 IoT");
  delay(500);

  Serial1.write(26);
  delay(500);
  readGSMResponse();

  Serial.println("SMS command sent. Check your phone for the message.");
}

void loop() {
  if (Serial1.available()) {
    char c = Serial1.read();
    Serial.write(c);
  }
}
4

It looks like the batteries are in parallel = 3.7 V is that correct?

From what I find it needs 5 V, so there's a difference of 1.3 V. Can it work with that? Another issue is that the Arduino works with 3.3 V, does the module have any voltage level translation for that?

5

Thank you for the suggestion. I will try with a series battery holder, and yes the sim module has a 3.3V TX and RX connection for the arduino

6

That will give 7.2 V instead. If the module is rated for 5 V only, it will certainly be fried.

For this setup to work you need three things:

  1. A battery holder that put the batteries in series, and in addition to that..
  2. a 5 V voltage regulator
  3. Edit: Not needed (Level conversion between 5 and 3.3 V, for the Tx and Rx pins)
7

Yes thank you for the suggestion and I am planning to buy an LM7805 5V Voltage regulator for the module

8

Those waste a lot of power as heat. Will your batteries last?

An LDO regulator will be much more friendly to your batteries.

9

I currently don't have an LDO regulator on hand and I can just recharge the batteries if they're out of power

10

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