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Rangkaian Sensor Cahaya dengan LDR

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LDR(Light Depending Resistor) adalah resistor yang nilai hambatannya bergantung dari intensitas cahaya yang ia terima. Jika intensitas cahaya rendah (gelap) maka nilai resistansinya akan menjadi sangat besar (mencapai 1MOhm atau lebih), sedangkan jika intensitas cahaya tinggi (terang) nilai resistansinya menjadi kecil (mencapai 10kOhm atau kurang). Sifat ini dapat kita pergunakan dalam rangkaian sensor cahaya.
Misalkan jika kita menginginkan sensor cahaya yang akan menyalakan lampu indikasi ketika ada cahaya dan mematikan lampu indikasi ketika tidak ada cahaya. Kita dapat menggunakan rangkaian seperti gambar di bawah ini.


Transistor NPN berfungsi sebagai gate. Arus dari kolektor akan mengalir menuju emitor jika arus dari base besar namun jika arus pada base kecil maka arus dari kolektor tidak akan menuju emitor.

Pada rangkaian sensor cahaya dengan LDR, ketika intensitas cahaya tinggi (terang) maka arus dari VCC akan melewati LDR kemudian melewati RESISTOR dan masuk ke BASE. Arus yang besar pada base menyebabkan arus dari VCC yang terhubung dengan kolektor diteruskan menuju emitor dan menyalakan LED (LED sebagai indikator saja).

Ketika intensitas cahaya redup (gelap) maka resistansi LDR begitu besar yang menyebabkan arus dari VCC sedikit sekali yang mengalir menuju base (arus pada base kecil). Hal ini menyebabkan arus dari VCC yang terhubung dengan kolektor tidak diteruskan menuju emitor dan akibatnya LED sebagai indikator tidak menyala.
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Comments

  1. EyuanaJanuary 26, 2013 at 12:22 AM

    Rangkaian anda sangat simple dan bagus jika difungsikan sebagai lampu penerangan otomatis

    ReplyDelete

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