Control 5V with 3.3V Using Light! (4N35 Opto-Coupler)

In this video, we explore how opto-couplers (opto-isolators) work using the popular 4N35.

Learn how you can safely control one circuit from another using light instead of a direct electrical connection—a powerful concept used in real-world electronics to protect sensitive components.

🔧 In this lesson, you’ll learn:

What an opto-coupler is
How the internal LED and phototransistor work
How to use a 3.3V signal to control a 5V circuit
Why electrical isolation is important
A complete working circuit example you can build

This is perfect for beginners, Arduino users, and anyone learning practical electronics.

00:00 Introduction
00:30 What is an Opto-Coupler?
01:20 Inside the 4N35 (LED + Phototransistor)
02:30 How Signal Transfer Works (Using Light)
03:45 Why Electrical Isolation Matters
05:00 Circuit Overview (3.3V Input → 5V Output)
06:30 Input Side Design (Resistor Calculation)
08:00 Output Side (Pull-Up Resistor Explained)
09:30 Full Circuit Demo
11:00 ON vs OFF Operation (Cutoff & Saturation)
12:30 Common Mistakes to Avoid
13:45 Real-World Applications
15:00 Final Thoughts
17:21 Going to the Lab!

👉 Full lesson notes & diagrams: https://buildcircuitswithrich.com/

Try the interactive simulation:
https://www.tinkercad.com/things/dTc5dJPJfL8-opto-coupler-circuit-4n35-33v-controls-5v
https://www.tinkercad.com/things/jpGCtJpC9xk-transistor-as-a-switch-cutoff-saturation

💡 Key takeaway:
You can transfer signals between circuits using light, keeping them electrically isolated and protected.

👍 If this helped you, consider subscribing for more hands-on electronics lessons!

#electronics #optoisolator #4N35 #arduino #circuits #beginnerelectronics

Видео Control 5V with 3.3V Using Light! (4N35 Opto-Coupler) канала Build Circuits With Rich