SIM800L GSM/GPRS Module
Compact cellular module for SMS, calls, and GPRS data.
Wiring & code for
SIM800L practical reference
A compact quad-band GSM/GPRS module enabling SMS alerts, calls, and basic cellular data connectivity from a microcontroller. Built around SIMCom's SIM800L chipset, it's smaller and more power-efficient than the older SIM900A while covering all four common GSM frequency bands, making it the more popular default choice today for SMS-notification systems, remote monitoring, and IoT projects that need cellular connectivity without Wi-Fi.
Key specifications
- Chipset: SIMCom SIM800L quad-band GSM/GPRS module
- Frequency bands: Quad-band 850/900/1800/1900MHz, broad global carrier compatibility
- Operating voltage: 3.4V–4.4V DC (breakout boards commonly regulate from a 5V input, but still require a supply capable of ~2A current spikes)
- Operating current: ~epsilon current in sleep mode, average ~70 mA idle-registered, spikes up to ~2A during transmit bursts
- SIM card: Micro-SIM card required (2G network only)
- Functions: SMS send/receive, voice calls, basic GPRS data (2G only — no 3G/4G support)
- Interface: UART, controlled via standard AT command set
- Form factor: Very compact compared to the SIM900A, popular for space-constrained builds
Pinout and connection notes
The SIM800L's power requirement is the single most common source of problems: it needs a dedicated 3.7-4.2V supply (often from a LiPo battery or a beefy buck converter) able to deliver short ~2A current spikes during transmit — powering it directly from an Arduino's 5V pin will cause random brownouts and resets. RX is 3.3V logic level and should be level-shifted or divided down from 5V microcontrollers.
- VCC: Power — requires a stable regulated 3.7-4.2V supply capable of ~2A peak current, NOT a standard 5V logic rail directly
- GND: Ground
- TX: UART transmit — connect to microcontroller RX
- RX: UART receive — connect to microcontroller TX (3.3V logic level, use a divider from 5V boards)
- RST: Module reset pin, active LOW
- SIM slot: Micro-SIM card holder on the underside of the board
- NET: Antenna connector — an external GSM antenna is essential for reliable signal
Integration checklist
- Confirm the exact part number and breakout-board revision.
- Verify supply voltage, current demand, logic levels, and signal direction against the datasheet.
- Check controller pin assignments and bus address or interface mode against the example code.
- Power up with external loads disconnected, then test signals before full integration.
- If readings or communication fail, check power and ground first, then pin mapping, interface settings, and library initialization.
Troubleshooting and reproducibility
Record the board used, wiring, library/version, supply arrangement, and measured behavior. Use the selected board-specific wiring example as the source of truth. Never assume visually similar modules share identical voltage tolerance or pin order.