GSM Remote Control Gate Control Schematic

Description: Power is supplied by continuous voltage, which is not always stabilized, applied to PWR + and - at a value between 5 and 32V. This voltage is filtered at the bottom by a diode (D1) that protects against polarity inversion, along with capacitors C1 and C2. Fuse F1 protects both the circuit and the power source in case of a short circuit in the integrated regulator. The 4 volts required for the rest of the circuit is generated by a switching regulator based on an MC34063 chip, configured as a series PWM regulator charged by inductance. The output voltage depends on the energy stored in inductor L1, and regulation is achieved through a resistive divider (R2/R3) to maintain the voltage at 4V across capacitors C4 and C5. Additional capacitors on the power lines of the microcontroller and GSM module filter the 4 volts, compensating for absorption peaks during transmission with capacitors C7, C8, C13, C14, C15, and C16, preventing disturbances to the microcontroller. The microcontroller managing the system is a PIC18F46K20-I/PT by Microchip, configured with an internal clock oscillator, though an external quartz oscillator is also included for firmware modifications. After initializing the I/O lines, the microcontroller checks the logical state of the opto-isolated inputs (RB4 and RB5) and the lines RC4, RC5, RD0, RD3, and RX, which are essential for receiving notifications from the cellular module. Specifically, RD3 detects incoming calls by interfacing with the RI of the cellular module, while RC4 controls the GSM reception LED (STATLED), which pulses at 1 Hz during network search and provides logical zero impulses for 0.5 seconds followed by a 2-second pause when a signal is detected. This behavior allows the PIC to assess the radio-mobile network conditions and act accordingly, such as delaying SMS or call attempts if there is no reception. The microcontroller's UART, accessible via pins 44 (TX) and 1 (RX), communicates with the cell phone, checking for received SMSs and facilitating calls. Control signals CTS, RTS, and DCD are utilized, along with RC5 and RD0 lines for GSM control and phone reset, respectively. The relay is activated by the microcontroller's RE2 line through two NPN transistors driven by current amplifiers, with a high logical state on RE2 saturating transistor T1.

The power supply circuit operates within a voltage range of 5 to 32V, indicating versatility in power source options. The diode D1 serves a crucial role in safeguarding the circuit from reverse polarity, ensuring that incorrect connections do not damage the components. The filtering capacitors C1 and C2 are essential for smoothing out voltage fluctuations, providing a stable input for the switching regulator.

The MC34063 switching regulator is a well-established component in power management applications, and its configuration as a PWM regulator allows for efficient energy conversion. The output voltage stabilization achieved through the resistive divider (R2/R3) ensures that the microcontroller and GSM module receive a consistent voltage level, critical for reliable operation. The inductor L1's energy storage capability directly affects the output voltage, making its selection vital for the desired voltage regulation.

The additional capacitors (C7, C8, C13, C14, C15, and C16) strategically placed along the power lines are designed to handle transient loads, particularly during GSM transmission, where current demands can spike significantly. This precaution prevents potential voltage drops that could disrupt the microcontroller's operation, thereby enhancing system reliability.

The PIC18F46K20-I/PT microcontroller is a robust choice for managing the system due to its processing capabilities and built-in communication interfaces. The inclusion of an external quartz oscillator provides flexibility for users who may want to customize the firmware for specific applications, which is a valuable feature in development environments.

The communication between the microcontroller and the GSM module via UART is critical for the functionality of the device. The control signals (CTS, RTS, DCD) facilitate effective data transmission, ensuring that the microcontroller can manage communication protocols seamlessly. The logic states on lines RC5 and RD0 provide additional control over the GSM module, allowing for power management and reset capabilities, which are essential for maintaining the operational integrity of the system.

Overall, this circuit design demonstrates careful consideration of component selection, voltage regulation, and communication protocols, resulting in a reliable and efficient system for managing cellular communications and power management.Power is supplied by continuous voltage, not always stabilized (applied to PWR + and -) at a value between 5 and 32V; such voltage is filtered at the bottom by the diode protecting against polarity inversion (D1) through condensers C1 and C2. Fuse F1 enables us to protect both thecircuit and the power source in case of a short circuit in the integrated regulator

discussed below, which is necessary to obtain the 4 volts needed for the rest of the circuit to work. The switching regulator is based on a MC34063 chip, utilized in the classic configuration of series PWM regulators charged by inductance, whose output voltage depends on the energy stored in L1; the regulator is stabilized by the component demoted from resistive divider R2/R3, which is needed to set at 4V the component leveled at the top of both C4 e C5.

The 4 volts at the bottom of the abovementioned condensers are sufficiently filtered by other condensers placed on the power lines of the microcontroller and of the GSM module; which presents, during transmission, absorption peaks compensated for by C7, C8, C13, C14, C15 e C16, thus avoiding that an impulsive current request may cause the microcontroller to be disturbed. The microcontroller used to handle the whole system is a powerful PIC18F46K20-I/PT by Microchip, which we use in its configuration with an internal clock oscillator; both the scheme and in the printed circuit are nevertheless equipped with external quartz, which we included for those who may want to modify the firmware and develop specific applications requiring an external oscillator.

Once the I/O lines have been initialized, the microcontroller verifies the logical state of the opto-isolated inputs at voltage level (RB4 and RB5) as well as that of lines RC4, RC5, RD0, RD3, RX, which are needed to receive the main notifications from the cellular module; more specifically, RD3 is used to detect incoming calls (it interfaces with RI of the cellular module), while RC4 controls the GSM`s reception led, whose output (dubbed STATLED) pulsates at a frequency of 1 Hz when the module is searching for the radio-mobile network, and supplies impulses at logical zero, lasting 0. 5 seconds and followed by a 2-second pause, when the module has grasped the signal. The frequency and duration of the impulses enable the PIC to understand the conditions of the radio-mobile network range and to behave accordingly; for example, if the opto-isolated input goes off and it needs, therefore, to send SMSs or make calls, but detects that the cellular module has no reception, it waits for the Telit module to get reconnected to the GSM/GPRS network before making any calls.

The attempt to make calls or send SMSs is repeated only three times, after which the device gives up. The microcontroller contains a UART accessible via pins 44 (transmission) and 1 (reception) which it uses in order to communicate with the cell phone; more precisely, through the first pin (TX), it cyclically questions the module in order to check whether any SMSs have been received, whereas both TX and RX are used to communicate with the GSM module when making calls and receiving or sending messages.

Regarding the UART, it is important to note that the following control signals are used: CTS (Clear To Send), RTS (Request To Send) and DCD (Data Carrier Detect), which correspond to those of the cellular module being used. They complete the set of I/Os destined to the cell phone, the RC5 and RD0 lines: the former controls the turning on and off of the GSM (though a transistor placed in the small board of the cell phone), while the latter takes care of resetting the cell phone.

As for the relay, it is controlled by the microcontroller`s RE2 line, through two NPN transistors driven by current amplifiers; line RE2 controls transistor T1. A high logical state causes the transistor to satu