SIM800L with Arduino: LED blinks, but no response in the serial monitor

[mamaji208]

Hello everyone,

I'm currently testing the SIM800L module with my Arduino UNO, but I'm having a problem: the module's LED flashes every second, which means that it's powered but can't connect to a network. What bothers me is that no data or response appears in the serial monitor.

Checks performed:

• The SIM card is inserted in the correct orientation.
• I used an adapter for the SIM card because it was too small.
• I disabled the SIM card's PIN code using my phone.
• The Arduino can send data to the serial monitor (tested separately with Serial.println("Hello, World!")).

Power supply for the SIM800L:

I know the SIM800L is very sensitive to power and requires a voltage between 3.7V and 4.4V.

• I used a diode to lower the voltage to 4.3V.
• I added a capacitor to handle current peaks.

Wiring:

I followed the schematic from this tutorial. In the article, the author uses a Raspberry Pi, but the principle should theoretically be the same—we just need a voltage between 3.7V and 4.4V.

Comment brancher et utiliser un module GSM SIM800L avec le Raspberry Pi (sans batterie).

Here is the schematic from the tutorial that I used as a reference:

And here is my own wiring diagram:

#include <SoftwareSerial.h>
SoftwareSerial sim800l(7, 8); // RX, TX

void setup() {
  Serial.begin(9600);
  sim800l.begin(9600);
  delay(1000);
  
  sim800l.println("AT"); // Communication test
  while(sim800l.available()) {
    Serial.write(sim800l.read());
  }
}

void loop() {
  // Handle AT commands here
}

Questions:

• Why is the serial monitor not receiving any response from the SIM800L? If I can get error messages, I'll have made progress and it'll be easier to debug.
• Is my power supply setup correct, or should I try a different solution?
• Are there any other points I might have overlooked?

Thanks in advance for your help!

[xfpd]

@mamaji208

SIM800L

Do you have the SIM800L isolated with an adequate power supply? I read "not greater than 4.0vdc". Is your transmit pin stepped-down to 3v3?

[mamaji208]

I take the 5v from the arduino, and lower the voltage to 4.3v (the diode drops 0.7v). I've seen that the voltage should be between 3.3v and 4.4v, so normally I'm good.

As I mentioned earlier, I've taken my inspiration from the diagram in this article because the principle is the same btw arduino and pi :

Comment brancher et utiliser un module GSM SIM800L avec le Raspberry Pi (sans...

[xfpd]

Other than no networks to connect, I would suspect power. Whether voltage too high, or power supply lacking cirrent.

[mamaji208]

I tried several circuits: with a diode like on my diagram I was at 4.4v when in theory I should have been at 4.3v. So I opted for an external power supply by buying a 3.7v battery directly, and I got the same result: no network found and above all I got NO result on the serial monitor (by sending the AT message)

Here's the link to the battery, I used the same one as a video tutorial:
[EEMB Batterie Lithium polymère 3,7V 1100mAh 603449 Batterie Rechargeable lipo avec connecteur JST avec VXI Blue Parrott - vérifier la polarité de l'équipement et du connecteur Avant l'achat : Amazon.fr: High-Tech](https://Amazon battery link)

I'm starting to despair lol, I'd at least like to have some feedback on the serial port to start debugging.

[xfpd]

Try 4vdc.