GSM modem circuit with Wavecom WMOi3

Modems are devices that connect remote devices to a computer or enable communication between multiple computers. While traditional modems typically use wired connections, the GSM modem described here operates wirelessly. It can link two computers, connect a computer to the internet, or serve as a central unit for a data acquisition system. The construction resembles a GSM phone but lacks keys and a display. Operation is facilitated through a serial interface using AT commands. The serial port can connect to a personal computer, laptop, or microcontroller. This modem-computer setup forms a network unit that is portable and can access other computers or terminal devices. For instance, this system can gather meteorological data and transmit it to any internet address or print it remotely. The modern GSM modem also provides opportunities to expand networks or initiate new applications that may be challenging to implement otherwise.

The circuit construction is relatively straightforward. It consists of a closed module based on the Wavecom model WMOi3 integrated modem, which operates on two frequency bands: E-GSM 900 and 1800MHz, adhering to Class 4 (2W at 900MHz) and Class 1 (1W at 1800/1900MHz). The exterior features a plug for antenna connection and a dual bar for all necessary connections. Proper string matching is essential to connect the modem to a computer. The module requires a 5V, 1A power supply to function.

Typical consumption is 300mA in GSM 900 mode at 2W, while standby consumption is only 9mA. The output and input RS232 lines operate at 3.3V levels. These levels can be adjusted to meet the voltage requirements of the RS232 interface using the integrated MAX3238 when connecting to a personal computer. However, if the modem is interfaced with an external microcontroller circuit, the microcontroller must operate at 3.3V for compatibility.

Implementing the modem is a relatively simple task. The necessary board is shaped appropriately, and bridges must be constructed as indicated in the accompanying figure. Care should be taken to avoid excessive soldering; the solder joints must be small and not too high to prevent short circuits. The primary challenge in construction lies in affixing the double string to support the module.

The contacts of the strings are spaced closer together than those of an integrated circuit, specifically at 2.54mm. Additionally, the strings are located on the printed side of the board, while the module is positioned on the copper side. An insulating layer of plastic should be inserted between the module and the board.

This arrangement may complicate circuit control. Prior to operating the circuit, a thorough inspection of the entire assembly for short circuits is necessary. After ensuring there are none, the board should be checked multiple times. The modem board connects directly to the MAX3238 board, with each row linked to the corresponding opposite row, ensuring proper communication and functionality within the circuit.Modems are devices that connect either remote devices to a computer, or two or more computers to each other. Their connection is usually wired. The GSM modem we present is wireless. It can connect two computers, a computer with the internet or even be the central unit for a data acquisition system.

Generally the construction is a GSM phone without keys and display. Its operation is easily accomplished by its serial door with AT commands. The serial port connects a personal computer, a laptop or a microcomputer. The modem and computer set creates a unit on a network. This system can be portable and at the same time have access to other computers or terminal devices. Suppose that this system is responsible for collecting meteorological data, whenever there are some reasons, the computer will pick up a phone from the cell phone and send the data to any internet address or simply to a printer in your office a lot Kilometers away. Modern GSM is another device that allows you to expand your network or start a new application that you would hardly start with.