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Rangkaian Sensor Infrared dengan Photo Dioda

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Keunggulan photodioda dibandingkan LDR adalah photodioda lebih tidak rentan terhadap noise karena hanya menerima sinar infrared, sedangkan LDR menerima seluruh cahaya yang ada termasuk infrared.

Rangkaian yang akan kita gunakan adalah seperti gambar di bawah ini.



Pada saat intensitas Infrared yang diterima Photodiode besar maka tahanan Photodiode menjadi kecil, sedangkan jika intensitas Infrared yang diterima Photodiode kecil maka tahanan yang dimiliki photodiode besar.

Jika tahanan photodiode kecil maka tegangan V- akan kecil. Misal tahanan photodiode mengecil menjadi 10kOhm. Maka dengan teorema pembagi tegangan:

V- = Rrx/(Rrx + R2) x Vcc
V- = 10 / (10+10) x Vcc
V- = (1/2) x 5 Volt
V- = 2.5 Volt

Sedangkan jika tahanan photodiode besar maka tegangan V- akan besar (mendekati nilai Vcc). Misal tahanan photodiode menjadi 150kOhm. Maka dengan teorema pembagi tegangan:

V- = Rrx/(Rrx + R2) x Vcc
V- = 150 / (150+10) x Vcc
V- = (150/160) x 5 Volt
V- = 4.7 Volt

Sekarang kita akan melihat trimpot. Trimpot adalah komponen pembagi tegangan dengan mengubah nilai resistansi yang ada di dalamnya. Dalam rangkaian ini maka nilai trimpot akan berkisar antara 5 Volt sampai 0 Volt. Nilai tegangan trimpot ini akan mempengaruhi nilai V+ yang diterima komparator sebagai nilai referensi komparator.

Komparator dalam rangkaian ini berfungsi untuk menghasilkan tegangan sebesar 0 Volt atau 5 Volt pada output komparator.
Jika V+ lebih dari V- maka output komparator = 5 Volt
Jika V+ kurang dari V- maka output komparator = 0 Volt.


Misal kita mengatur besar V+ dengan cara memutar putaran pada trimpot hingga dihasilkan tegangan sebesar 3.5 Volt.
Pada saat intensitas infrared besar yang mengakibatkan tahanan Photodiode mengecil menjadi 10 kOhm dan mengakibatkan V- = 2.5 Volt maka output komparator menjadi 5 Volt.
Pada saat intensitas infrared kecil yang mengakibatkan tahanan Photodiode membesar menjadi 150 kOhm dan mengakibatkan V- = 4.7 Volt maka output komparator menjadi 0 Volt.

Untuk pengujian kita dapat menggunakan LED sebagai indikator rangkaian seperti gambar berikut ini.

Penghubungan Output komparator dengan Vcc bertujuan sebagai rangkaian PullUp. Hal ini dikarenakan arus yang keluar dari komparator begitu kecil sehingga walaupun memiliki nilai tegangan sebesar 5Volt tidak dapat diterima beban (dalam rangkaian diatas beban adalah LED). Dengan penambahan Vcc,
ketika tegangan output dari komparator berniali 0 Volt maka arus dari Vcc lebih banyak memilih mengalir menuju output komparator yang bernilai 0 Volt dan tanpa beban.
ketika tegangan output dari komparator bernilai 5 Volt maka arus dari Vcc akan banyak mengalir menuju LED kemudian ke ground yang mengakibatkan LED menyala.

Skematik Komparator



Penempatan Pin IC LM339M yang berisi 4 buah komparator



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Comments

  1. UnknownDecember 14, 2020 at 6:21 PM

    Itu pake photodioda ama ir led yg ukuran berapa? 3 apa 5?

    ReplyDelete
    Replies
    1. Luki B. SubektiDecember 15, 2020 at 2:57 PM

      bisa pakai keduanya, 5mm atau pun 3mm.
      kalau 5mm jarak penempatan komponen bisa dibuat lebih renggang.
      kalau untuk percobaan awal, pakai 5mm saja.

      Delete
  2. AnonymousJune 23, 2021 at 1:25 PM

    Kalo umpama antara Ir LED sama photodiode beda ukuran bisa kah?

    ReplyDelete
    Replies
    1. Luki B. SubektiJune 23, 2021 at 2:16 PM

      bisa, tidak masalah. tapi besarnya LED (intensitas cahayanya) pasti akan mempengaruhi besarnya tahanan dari photodiode yang dihasilkan.

      misal, dari contoh di tulisan di atas, ketika photodiode menerima pantulan cahaya dari LED, tahanannya menjadi 10kOhm.
      namun misal, LED diganti dengan yang intensitasnya lebih kecil, ketika photodiode menerima pantulan cahaya yang lebih sedikit, mungkin tahanannya membesar menjadi 50kOhm.

      akibatnya tegangan referensi komparator (V+) perlu disesuaikan (dengan mengatur trimpot). untuk contoh ini, karena tahanan photodiode menjadi lebih besar, V- akan menjadi lebih besar, sehingga V+ dapat dinaikkan misal menjadi 3.8V dari yang sebelumnya 3.5V.

      Delete
  3. AnonymousAugust 16, 2022 at 1:50 PM

    Cara kerjanya gimana ya kak?

    ReplyDelete
  4. AnonymousJanuary 24, 2023 at 10:53 AM

    Trimpot sudah d putar tp nilai reasuransi tidak berubah..ketika photodioda kondisi gelap.nilai resitandi naik.. kira2 rangkaian apa yg rusak ya mas?

    ReplyDelete
    Replies
    1. Luki B. SubektiJanuary 24, 2023 at 1:58 PM

      kalau nilai resistansi atau tegangan keluaran trimpot tidak berubah ketika diputar, kemungkinan besar trimpotnya rusak. coba ganti dengan trimpot yang baru.

      untuk pengetesan, pisahkan rangkaian trimpot dari rangkaian utama terlebih dahulu, ukur tegangan keluaran trimpot terpisah dari rangkaian utama.

      Delete
  5. AnonymousAugust 23, 2025 at 2:35 PM

    Apakah komparator bisa diganti menjadi op amp 741? Trimpot yang digunakan berapa ohm?

    ReplyDelete
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