## 2 Materials and Methods
### System Architecture  
#### 2.2.1 Initial Development  
The process of coupling or decoupling switch heaters, involves transmitting a written message (e.g., ON as 01 and OFF as 10) from a mobile terminal, which is received by a GSM modem in the power supply box, located near the switches. The modem then delivers the message to the remote control system (RCS) as an electrical signal, which triggers the coupling or uncoupling of the power contacts supplying the PSPs. Upon execution, a confirmation message is sent back to the mobile device. Figure 5 illustrates the control system of a resistive heater remote, through the GSM network [20,21]. The RCS assembly consists of several components, including an 8-bit microcontroller, a GSM modem, a voltage regulator, an RS232 serial communication module, and other electronic parts such as optocouplers, diodes, transistors, capacitors, and a 12 V relay. These components are mounted on wiring made in ExpressPCB, as shown in Figure 6[22,23]. Figure 4: Platform lighting scheme for a railway station. PSP = power supply panel; L = rail line, Roman numerals = direct lines; Arabic numerals = branching lines. Figure 5: Diagram of the command system of resistive heating of railway switches using GSM networking. RCS = remote control system; DB = distribution block; PSP = power supply panel. The 40-pin, 8-bit PIC16F887 microcontroller (Microchip, Chandler, AZ, USA), uses nanoWatt technology and has a 40-pin design. Its low cost and user-friendly architecture, make it affordable and simple to use and modify. The GSM Maestro 100 modem is used by the microcontroller to implement communication between the railroad switch and the SMS sender, at a speed of 300 bits per second (bps) over the serial port. A voltage regulator, LM2575-5 (Texas Instruments, Dallas, TX, USA), of 1 A, is utilized to reduce the supply voltage from 12 V continuous to 5 V continuous, which is needed for the PIC microprocessor (Microchip, Chandler, AZ, USA) and MAX232 IN (Texas Instruments, Dallas, TX, USA) circuit. Using a 330-H coil and the voltage regulator mentioned above, a consistent power supply distribution is created [22; 24]. The MAX232 IN integrated circuit is used as a converter of logical (0/1 logic) impulses into RS232 signals (+8/-8 V), that are accepted by the GSM modem. In addition, for added security, the LTV825 optocoupler is used, which acts as a bridge between the microcontroller's logic levels of control (0/1) and the final command transistor BD139. A continuous voltage level of 12 V and a maximum current of 1.5 A pass through the transistor. This signal is used to control a relay for a railroad switch, and the relay in question will direct a 220 V AC voltage level to a power contactor. Upon decoupling, the 1N4007 diode, in series with the 12 V relay coil, achieves the protection of the BD139 transistor. The microcontroller issues the command to the optocoupler through the output pin. By passing the ground connection through an auxiliary contact on the 12 V relay, the (open/closed) state of the relay is read. The microcontroller's input pin 10 (RE2 pin), which is designated as the input pin, detects the presence or absence of the ground. The two-pin modem and the PIC16F887 communicate via MAX232: TX for transmission and RX for receiving characters from the modem. AT commands are a set of instructions used to control modems, where AT stands for attention. Each command line must start with \"AT\" followed by the specific command. The system described in this study utilizes the following AT commands: AT + CMGD = 1.4, for deleting all messages stored in the SIM card; AT + CMGS, for sending SMS messages; and AT + CMGR, for reading SMS messages received by the modem and processed by PIC16F887. The programming of PIC16F887 was carried out using the PICKit 2 programmer and written in the C language. The integrated development environment (IDE) utilized, was MPLAB v8.10, and the compiler HI-TECH PIC C Lite 9.60 was used to compile the program.