SIM900A modem is designed from SIMCOM. This miniature GSM/GPRS modem can be integrated into a great number of IoT projects. It operates on frequencies 850MHz, 900 MHz, 1800 MHz, and 1900 MHz. This small size and easy to use as a plug-in GSM Modem. Using the AT command the baud rate is configurable from 1200-115200.
This SIM900A 5V V4.0 Kit Wireless Extension Module GSM GPRS Board consists of two sets of on-board power supply interface VCC5 5V power supply, VCC4 interface, 3.5–4.5V power supply, optional power on self-starting (default), and control start. And also an onboard SMA (default) and IPXmini antenna interface, allows SIM900A interface reserved reset.
In this module, the computer is capable of giving early computer debugging USB module power supply, and a very large amount of data under the condition of the recommended current of more than 1A. Furthermore, it has Standby hundreds of MA data that may be adjusted to give dormancy, 10MA low power dormancy. In addition, it supports two mobile phones, three different types of cards, and four different types of cards. This TTL-level module is perfectly compatible with 3.3V and 5V. Here The SIM card circuit was created to boost the SMF05C ESD chip. This SIM900 wireless extension Antenna circuit ensures that the signal path is short and straight, resulting in increased signal strength.
The control interface of each pin description:
- GND – GND
- SIMR SIM900A RXD, TTL level, cannot be linked to the 232 level directly.
- SIMT SIM900A TXD, TTL level, cannot be linked to the 232 level directly.
- RST – SIM900A reset, active low
- VCC MCU When the SIM900A module and 5V TTL level communication, this pin is linked to DC 5V; when the SIM900A module and 3.3V TTL level communication, this pin is connected to DC 3.3V.
- VCC5—-DC 5V input.
- VCC4——DC3.5–4.5 input