LAN infrared remote control transmitting and receiving circuit diagram

0805 red light emitting diode

The system utilizes the AT89C51 microcontroller from the 51 series, a low-voltage, high-performance CMOS 8-bit microprocessor with 4KB of Flash memory that can be programmed and erased. This device is commonly referred to as a microcontroller and is built using ATMEL’s advanced non-volatile memory technology. It is fully compatible with the standard MCS-51 instruction set and output pins. By integrating a powerful 8-bit CPU with Flash memory on a single chip, the AT89C51 offers an efficient and cost-effective solution for various embedded control applications. The microcontroller features 40 pins and 32 bidirectional I/O ports, along with two external interrupt inputs, two 16-bit programmable timers, and a full-duplex serial communication port. It can be programmed either through conventional methods or via online programming, offering flexibility in development. For the infrared transmission module, the key challenge lies in ensuring that the signal sent by the microcontroller is correctly recognized by the infrared emitting diode and that the signal is properly transmitted. An infrared LED is used for this purpose, which emits infrared light with a wavelength around 940 nm. These LEDs are similar in shape to regular LEDs but emit invisible light instead of visible light. They come in black or transparent colors and are widely used in remote controls. There are two main types: one for long-range remote control signals and another for short-range applications that combine both emission and reception. Since this design is for a home remote control, the long-range type is suitable. As shown in the schematic, the system uses P1.0 as the input key port and P2.0 as the infrared output port, sending a 38kHz carrier signal. The signal is amplified by a 9013 NPN transistor before being emitted through the IR LED. The reset pin (pin 9) is connected to an RC circuit for manual resetting, while pins 18 and 19 are connected to a crystal oscillator for timing. The infrared receiving module works in conjunction with a relay-based dimming circuit. Each relay is controlled through resistors connected in parallel to the P0 port. When more relays are activated, the brightness increases. For example, all four relays on produce maximum brightness, while only one relay produces the lowest. If no relays are active, the lamp is turned off. The receiving circuit diagram is illustrated in Figure 6. The SM0038 infrared receiver has a center frequency of 38kHz, matching the transmission frequency. This circuit uses a single button to send encoded signals, and the receiving end adjusts the brightness based on the number of received codes. Every time the P1.0 port goes low, it indicates a key press, triggering a code transmission through P2.0. Upon receiving the signal, the system checks if the initial low level lasts longer than 2ms, then verifies the code. If correct, the brightness is adjusted accordingly. One of the main challenges in this design was achieving reliable infrared signal transmission and reception. Using software-based encoding and decoding simplifies the circuit, enhances flexibility, and reduces costs. A single button can control both switching and dimming of a light, and with a matrix keyboard, the entire home lighting system can be managed efficiently, making this design practical and user-friendly.