The circuit of construction is relatively simple. The whole construction is a closed module of the wavecom model WMOi3 integrated modem. It works on two bands E-GSM 900 and 1800MHz and obeys Class 4 (2W 900MHz) and Class 1 (1W 1800 / 1900MHz). Outside, it has a Plug for connecting the antenna and a double bar where all the connections will be made. String matches are the necessary data to connect to a computer. The module to work needs a 5V and 1A power supply.
The average consumption is 300mA in GSM 900 and 2W. In standby, it consumes only 9mA. Output and input RS232 lines have reasonable levels of 3.3v. These levels can get the voltage levels that the R5232 wants with the integrated MAX3238 if we are going to connect the construction to a personal computer. But if we combine the modem with an external microcontroller circuit, the microcontroller should work at 3.3v for compatibility reasons.
Implementing the modem is a relatively simple matter. The necessary board is in the shape. On this board we will make the bridges shown in the following figure. Here we must be careful not to overdo it. Welds should be small and not too high. At the same time, there should be no short circuits due to welding or other cause. The difficulty in construction is in the gluing of the double string to support the module.
The contacts of the strings have a shorter distance than the terminals of an integrated one, ie 2.54mm. Additionally, the strings are located on the printed side. The module is finally placed on the same side as copper. Between the module and the board an insulating surface of some plastic must be inserted.
This placement results in difficulty in controlling the circuit. Before putting the circuit in operation, carefully examine the whole block for any short circuits. When you make sure it does not, then check again and again the plaque again, once again. The modem board connects directly to the MAX3238 board. Each row is connected to the one opposite one.