ESP32 Bit Pirate

ESP32-S3 AT command and cellular debugging

Send AT commands to cellular modems with ESP32

ESP32 Bit Pirate turns a compatible ESP32-S3 board into an AT command and cellular modem debugging workbench. Use it to test UART AT devices, check modem status, inspect SIM details, verify network registration and run SMS or USSD workflows.

Start with the UART AT helper Flash ESP32 Bit Pirate
AT command and cellular modem debugging visual with an ESP32 board, modem and SIM card

Quick AT workflow

Start with the electrical and UART basics, then move into modem status and SIM/network checks before sending commands that affect a real service plan.

  1. 01

    Connect TX, RX and GND between the ESP32 Bit Pirate and the AT module or modem.

  2. 02

    Confirm voltage levels, modem power and baud rate before opening the AT helper.

  3. 03

    Send a basic AT command and wait for a clean response before deeper testing.

  4. 04

    Check modem status, SIM state and network registration before SMS or USSD.

  5. 05

    Continue with the recipe that matches the next task: status, SIM, network, phonebook, USSD or SMS.

mode uart
at
mode cell
status
sim
network
sms
ussd

Example CLI flow. See the UART and CELL wiki pages for exact syntax, supported modem behavior and firmware-specific options.

AT workflows covered by ESP32 Bit Pirate

Use this overview to choose the right AT or cellular workflow before opening a detailed recipe.

UART

AT command helper

Send guided AT commands to modems, GPS modules and serial devices that use command/response text protocols.

Status

Modem bring-up checks

Confirm that the modem is powered, reachable and ready before debugging a higher-level cellular workflow.

SIM

SIM card inspection

Read SIM status and identifiers so absent, locked or unready SIM states are visible early.

Network

GSM/LTE registration

Check registration state, signal information and operator visibility before trying data, USSD or messaging.

USSD

Operator service requests

Run USSD only after the SIM and network path are known good, and only on your own authorized service.

SMS

Message send workflow

Open the SMS workflow after modem, SIM and registration checks have removed the usual setup failures.

When an AT workbench helps

AT problems can look like firmware bugs, wiring mistakes, power failures or operator issues. A small external workbench lets you separate those layers before changing target code.

Bring-up

Before writing modem firmware

Prove that the modem responds to basic AT commands and that the UART wiring is correct.

Cellular

Before debugging the application layer

Check SIM, registration and signal state before spending time on HTTP, MQTT or SMS code paths.

Serial module

Before guessing command syntax

Use the UART AT helper to test line endings and responses from AT-style modules in a controlled shell.

AT hardware and service reminders

These checks keep the workflow practical without repeating the detailed command pages.

TX/RX

Cross TX to RX, RX to TX and always connect a common ground before expecting a modem response.

Voltage

Check UART voltage levels. Do not connect 5 V serial directly to a 3.3 V ESP32-S3 pin without level shifting.

Power

Cellular modems can draw burst current. Use a proper modem supply instead of assuming USB power is enough.

Antenna

Attach the correct antenna before registration, signal or operator tests.

SIM

Use your own SIM card, know whether it requires a PIN and expect operator charges for SMS or USSD services.

Authorization

Send AT commands, SMS and USSD only on hardware, SIMs and networks you own or are explicitly allowed to test.

Common AT problems

Most AT failures are wiring, baud rate, power, SIM or registration problems. Check these before treating the modem as broken.

No response

Check TX/RX orientation, common ground, baud rate, line ending behavior and whether the modem is awake.

Random text

Try the expected baud rate again, then use UART diagnostics before assuming the AT command is wrong.

SIM not ready

Check SIM insertion, PIN state, carrier activation and whether the modem supports the SIM/network combination.

Not registered

Check antenna, signal, operator availability, band support and service plan status.

SMS or USSD fails

Confirm modem status, SIM readiness and network registration before opening the SMS or USSD workflow.

Detailed AT and cellular recipes

These pages are the task-level AT and cellular workflows. This overview keeps the protocol-level guidance here, while each recipe covers commands and troubleshooting in detail.

Useful AT references

This page is a protocol overview. Use the site index for the full web experience, or GitHub for source code, firmware documentation and the AT/CELL command references.

Flash ESP32 Bit Pirate

Flash a supported ESP32-S3 board before testing AT modem mode from the browser.

Open Web Flasher

CELL command reference

Open the maintained firmware wiki for cellular modem status, SIM, network, SMS and USSD commands.

Open CELL command reference

UART command reference

Use UART mode documentation for serial setup, AT helper behavior and lower-level link checks.

Open UART command reference

ESP32 Bit Pirate GitHub

Check firmware source, issues and releases that affect AT modem support.

Open GitHub repository

AT command debugging FAQ

Short answers for common questions before moving into a detailed workflow.

Can ESP32 Bit Pirate send AT commands to a modem?

Yes. ESP32 Bit Pirate can use UART mode and the AT helper to send guided AT commands to modems and serial modules.

Can ESP32 Bit Pirate check cellular modem and SIM status?

Yes. CELL mode can check modem status, SIM information and network registration before SMS, USSD or other cellular workflows.

Should I send SMS or USSD commands before checking the modem state?

No. Start with modem status, SIM status and network registration, then use SMS or USSD only with your own SIM and authorized service plan.