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SIM800L Driver

Driver for the SIMCom SIM800L GSM/GPRS (2G) module.

Hardware requirements

The SIM800L operates at 3.7-4.2V and can draw up to 2A during transmission bursts. Make sure your power supply can handle this.

  • Do not power the module from the ESP32's 3.3V or 5V pins. The 3.3V is too low, and 5V exceeds the module's maximum voltage rating.
  • A LiPo battery (3.7V, 1200mAh+) or a 2A-capable DC-DC converter is recommended.
  • Some boards (like the LilyGO T-Call) include a power management IC.
  • The SIM800L uses ~2.8V logic levels. The ESP32's 3.3V TX cannot be connected directly to the SIM800L RX — use a voltage divider or level shifter.

Pin connections

SIM800L Pin Description
VCC 3.7-4.2V power supply
GND Ground
TXD Module transmit → ESP32 UART RX
RXD Module receive ← ESP32 UART TX
RST Active-low reset (pull low to reset)
PWRKEY Power toggle (pulse low >1s to toggle on/off)

Usage

Installation

Install the driver as a container on the device:

jag container install sim800l src/modules/simcom/sim800l.toit

LilyGO T-Call board

The T-Call board has a power management IC (IP5306) controlled by GPIO 23 that must be enabled before the SIM800L module can be used. The T-Call example provides a custom service provider that manages the power IC automatically — it enables the IC when the network is opened and disables it when all clients disconnect. Install the T-Call wrapper instead:

jag pkg install --project-root examples/
jag container install sim800l examples/sim800l-tcall.toit

T-Call pinout:

Function GPIO
UART TX 27
UART RX 26
RST 5
PWRKEY 4
POWER_ON 23

Configuration

import net.cellular

config ::= {
  cellular.CONFIG-APN: "your-apn",
  cellular.CONFIG-UART-TX: 27,
  cellular.CONFIG-UART-RX: 26,
  cellular.CONFIG-POWER: [4, cellular.CONFIG-ACTIVE-HIGH],   // PWRKEY
  cellular.CONFIG-RESET: [5, cellular.CONFIG-ACTIVE-LOW],    // RST
  cellular.CONFIG-LOG-LEVEL: log.INFO-LEVEL,
}

network := cellular.open config

Example

See examples/sim800l.toit for a complete example that does an HTTP GET over the cellular network.

Limitations

  • 2G (GSM/GPRS) only — no LTE support.
  • Maximum 6 simultaneous TCP/UDP connections. Opening a 7th connection throws a ResourceExhaustedException.
  • Maximum ~1460 bytes per single AT send command. TCP writes are automatically chunked by the driver; UDP sends that exceed the MTU (1460 bytes) throw an error.
  • No hardware flow control (RTS/CTS) support in most configurations.
  • The PWRKEY pin toggles power on/off, so the driver only pulses it once during initialization to avoid toggling the module off.