Sistem komunikasi cahaya (VLC) merupakan satu teknologi baru dalam bidang komunikasi tanpa wayar yang terdiri daripada penghantar dan penerima dengan menggunakan cahaya sebagai bahantara penghantaran. Untuk penghantar, Diod pemancar cahaya (LED) digunakan pada VLC atas keupayaan pensuisannya pada frekuensi tinggi. Oleh sebab LED tidak boleh menghantar data dengan sendiri, litar pemacu pemancar khas untuk penghantaran data dan pencahayaan perlu direka. Keupayaan pensuisan Transistor Simpang Dwikutub (BJT) 2N3904 pada frekuensi tinggi digunakan dalam rekabentuk litar pemacu pemancar LED. Litar keseluruhan kemudian difabrikasikan kepada papan litar tercetak (PCB). Pengesahan terhadap prestasi litar pemacu pemancar LED termasuk gelombang isyarat keluaran dilakukan. Keputusan eksperimen menunjukkan bahawa pemacu pemancar LED dapat menghantarkan data sehingga 500kHz. Untuk penerima, ia terdiri daripada tiga peringkat, iaitu litar penguat transgalangan (TIA), litar penguatan voltan, dan litar keputusan. Fotodiod digunakan dalam penerima untuk menukarkan isyarat cahaya kepada arus elektrik. Oleh sebab voltan lagi mudah untuk proses, arus elektrik tersebut ditukarkan oleh TIA kepada voltan. Seterusnya, voltan tersebut dihantarkan ke litar penguatan voltan. Lepas itu, voltan yang dikuatkan dihantar ke litar keputusan untuk menghasilkan gelombang segiempat sama. Litar keseluruhan kemudian difabrikasikan kepada PCB. Frekuensi operasi maksimum penerima ialah 100kHz dengan jarak 20cm daripada penghantar. Pengiraan lebah jalur TIA ialah kira-kira 300kHz. Perbezaan sudut mendatar antara penghantar dan penerima ialah ±5ᴼ. Projek ini telah membuktikan bahawa penghantar berjaya menghantarkan data dan penerima berjaya menerima dan memulihkan data yang dihantarkan oleh penghantar.
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Visible light communication (VLC) system is a new high speed wireless communication technology that consists of a transmitter and a receiver which uses white light as the transmission medium. For the transmitter, light emitting diode (LED) has been selected due to its ability to switch at high speed. However, LED cannot transmit data on its own. Therefore, a driver circuit that can perform both data transmission and illumination purpose is design. BJT 2N3904 is chosen as the main component of transmitter driver design due to its high speed switching characteristics. The overall circuit design of the transmitter is fabricated into PCB and the performance of the transmitter driver is verified in term of the output signal characteristics. The experimental results show that the transmitter driver able to transmit data up to 500kHz. For the receiver, it is consists of three stages of circuit, which are TIA circuit, voltage amplification circuit and decision circuit. Photodiode is used in the receiver to convert light signal into electrical current. The electrical current is converted into voltage by the TIA circuit since voltage is easier to process. Next, the voltage is passed to voltage amplification circuit and this amplified voltage is then sent to the decision circuit to produce a perfect square wave output. The complete circuit is finally fabricated into PCB. The maximum operating frequency of the receiver is 100kHz at a fixed distance of 20cm from the transmitter. The bandwidth of TIA circuit is approximately 300kHz by calculation. The maximum horizontal angle difference between the transmitter and receiver to receive transmitted data correctly is ±5ᴼ. It is proven that the LED transmitter is able to transmit data and the receiver is able to receive and recover the data sent by the transmitter correctly.
Development of led transmitter and photodiode receiver for visible light communication / Neo Chan Seng