LED Current Limiting Resistor Experiment

Introduction

LEDs (Light Emitting Diodes) are efficient but delicate components that require a resistor to limit the current. This tutorial explains how to calculate and connect the correct resistor to protect your LED and demonstrates the practical application of Ohm's Law in circuit design. By the end of this tutorial, you'll have a solid understanding of current-limiting resistors and their importance in circuit design.

Circuit Diagram

Here’s a simple schematic for connecting an LED with a current-limiting resistor:

• V_in: Input voltage (e.g., 5V USB)
• R: Current-limiting resistor
• LED: Light Emitting Diode

Resistor Calculation

Use Ohm's Law to determine the required resistor value:

R = (Vin - VLED) / I

For a 5V supply, 2V LED forward voltage, and desired currents:

• 20mA: R = (5V - 2V) / 0.02A = 150Ω
• 15mA: R = (5V - 2V) / 0.015A ≈ 200Ω

Tip: Use a 220Ω resistor for a safe, long-lasting setup, as it limits current to about 13.6mA.

Required Components

• 220Ω Resistor (1/4W)
• 3mm Blue LED
• Mini Breadboard
• Micro USB Breakout
• Soldering Kit (optional)

Assembly Steps

Step 1: Place the LED

Insert the LED into the breadboard. Ensure the anode (long leg) and cathode (short leg) are in separate rows.

Step 2: Connect the Resistor

Connect one end of the resistor to the cathode of the LED and the other end to the breadboard’s GND row.

Step 3: Wire the Power Supply

Connect the LED’s anode to 5V and the resistor’s free end to GND.

Step 4: Test the Circuit

Power the circuit and observe the LED brightness. Adjust resistor values if needed for different currents.

Experiment

Test various resistor values (e.g., 150Ω, 220Ω, 330Ω) to compare LED brightness and current consumption. Record and analyze the results.

Here's how the current impacts brightness:

• Lower resistance = Higher current = Brighter LED (but shorter lifespan).
• Higher resistance = Lower current = Dimmer LED (but longer lifespan).

Experiment with these configurations to find the optimal balance for your project.

Advanced Techniques

For more precise control, consider using a variable resistor (potentiometer) to adjust the current dynamically. This setup is useful for applications requiring adjustable brightness.

• 10k Ohm Potentiometer

Applications

• Indicator lights
• Control panels
• Decorative lighting
• Development board indicators
• Basic DIY electronic projects
• Interactive art installations

Common Mistakes

• Forgetting to use a resistor, which can damage the LED permanently.
• Using a resistor with an incorrect value, resulting in either no light or a burned-out LED.
• Reversing the LED polarity (anode and cathode connections).
• Supplying excessive voltage to the circuit without proper calculations.

Always double-check your circuit connections and calculations to avoid these issues.

Conclusion

By understanding and applying resistor calculations, you can protect LEDs in various circuits, enhancing safety and longevity. Experiment with different setups to explore further possibilities. Whether you're a beginner or an experienced maker, mastering LED circuits is an essential skill in electronics.