Each set of serial data output waveforms from the VD5026-4 includes a synchronization pulse, a 12-bit encrypted address and control data, and a single stop bit. The pulse sequence is arranged in the order of AO to A7, followed by A8/DO to All/D3. Each group of serial data is transmitted at least four times to ensure reliability. Once the serial data format, verification method, pulse period, duty cycle, and their corresponding relationships are understood, the application program can be developed according to the encoding pulse output requirements, enabling the microcontroller to perform the encoder's functions. The block diagram of the analog encoder is illustrated below.
The infrared remote control keyboard designed using this technology has been successfully applied in a "color remote monitoring system." The working principle of the remote keyboard is shown below. This circuit uses a single-chip microcontroller, the AT89C2051, which is a cost-effective solution. It is based on the 80C31 core and fully compatible with the MCS-51â„¢ architecture. The device features 2 KB of reprogrammable flash memory, supporting up to 1,000 programming cycles, with data retention for up to 10 years.
The VD5027 decoder provides 4-bit data output, capable of representing 16 different states, which meets the needs of a 3×4 keyboard layout. When the MCU detects a key press, it generates a corresponding code pulse. This signal is modulated with a 38 kHz carrier wave and transmitted via an infrared emitting diode (SE303A). The received infrared signal is converted into an electrical signal by an infrared receiving diode (PH302B), then amplified by the CX20106 infrared receiver, resulting in a pulsed electrical signal.
After signal shaping and amplification, the encoded pulse is restored and sent to the 14-pin DIN input terminal of the VD5027 decoder. Upon receiving the first series of encoded pulses, if they match the pre-set address, the four-bit data (DO-D3) is stored in the register and converted from serial to parallel format. When the second identical pulse sequence arrives, the address is verified again. If both the address and control data match, the internal logic circuit of the VD5027 sends a control signal, transferring the data from the register to the DO-D3 output pins. At the same time, the TV terminal switches from low to high level, indicating that the decoding is valid.
Once the host receives the valid decoding signal, it reads the DO-D3 output from the VD5027, decodes the key value, and executes the corresponding action. This system ensures accurate and reliable communication between the remote control and the target device, making it ideal for applications such as home automation, surveillance systems, and more.
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