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I'm trying to interface a SIM A7670C GSM/GPRS module with an ESP32, but I'm encountering some issues in receiving proper responses using AT commands. Below are the steps I've taken so far:

Direct Connection to ESP32:

I connected the SIM A7670C module directly to the ESP32, providing a 3.5V power supply to the module. I connected the TX/RX pins of the module to the RX/TX pins of the ESP32. I sent AT commands via the ESP32, but there was no response from the module.

Using a Level Converter:

I used a level converter to shift the voltage levels of the TX/RX pins of the SIM A7670C module from 1.8V to 3.4V to match the ESP32. After making the connections and sending AT commands, I received an "ERROR" response. esp32 with SIM A7670C using Level Converter

Using a USB to TTL Converter:

I connected the SIM A7670C module directly to a USB to TTL converter. Without sending any AT commands, I received the following responses from the module:

*ATREADY: 1 
+CPIN: READY 
SMS DONE

*ATREADY: 1 
+CPIN: READY 
SMS DONE

These responses were received without issuing any AT commands. SIMA7670C with USB to TTL

Given these results, I'm unsure why the module is not responding correctly when interfaced with the ESP32. Could anyone suggest what might be going wrong or recommend any additional steps to troubleshoot this issue?

Additional Information:

The SIM A7670C module operates at 1.8V for its TX/RX pins. The ESP32 operates at 3.3V for its TX/RX pins. I have ensured that the power supply to the module is stable. Any help or guidance would be greatly appreciated!

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  • Hi Vaibhav, welcome to SO. In scenarios 2 and 3 the GSM module is responding, so communication is up and running. An ERROR response means you issued a bad command. Messages like *ATREADY: 1 +CPIN: READY SMS DONE are commonly sent by GSM modules after boot. Since you've not described which commands you're trying to send to the GSM module and what serial configuration (e.g. baud rate) you've set up there's nothing much we can do for you. Please take the Tour and read How do I ask a good question?. Commented Aug 22, 2024 at 17:45
  • If you received those messages, that's means that your UART connection is correct, but it also means that none of the two wiring diagrams are correct. Please provided your actual connection, and how and what exactly you send the AT command. Commented Aug 23, 2024 at 11:20
  • i THINK the Tarmo answer is unjustified.I have the same problem, no input to the module seem to be accepted, and the module repeats the sequence as described ending with SMS done. I find no explanation in simcom's AT commond app note, as to what the module intends by this repetition. Commented Nov 5 at 13:26
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