The SIM900A HW-353 module enables GSM voice, SMS, and GPRS data communication over 2G networks. With TTL serial interface and onboard SIM slot, it integrates easily with Arduino, ESP32, and STM32 systems. Includes SMA antenna and IPX connector for flexible RF deployment.

Specifications

• Chipset: SIM900A (GSM/GPRS quad-band)
• Frequency Bands: 850 / 900 / 1800 / 1900 MHz
• Communication Modes: Voice, SMS, GPRS (Class 10)
• Interface: TTL UART (RXD/TXD, 3.3 V or 5 V compatible)
• Operating Voltage:
  • VCC5: 5 V DC (≥ 1 A recommended)
  • VCC_MCU: 3.3 V or 5 V (logic level selection)
• SIM Slot: Flip-type SIM card holder (standard SIM)
• Antenna Interface:
  • SMA female (bend type)
  • IPX mini connector (optional)
• Audio Interface: MIC and SPK pads (mono voice)
• Control Pins:
  • RST (active low reset)
  • SIMT/SIMR (TX/RX)
  • S0–S3 (optional control)

Features

• Supports voice calls, SMS messaging, and GPRS data
• TTL-level serial interface for direct MCU connection
• Dual power input options for flexible integration
• Onboard SIM slot and antenna interface for plug-and-play deployment
• Compatible with Arduino, STM32, ESP8266, and ESP32
• Common use cases:
  • Remote monitoring and SMS alert systems
  • GSM-based IoT telemetry nodes
  • SMS-controlled relays and automation

Some SIM900A modules require firmware reflash. If you are seeing the network indicator blinks fast continuously even after inserting a valid sim, then most probably the firmware need to be updated. If you are incapable of handling such a task with a USB to TTL module such as the FT232 module, then this module isn't suitable for you. In case the firmware needs to be updated, following tools could be helpful.

Serial Tool
Custom Flasher
Firmware