2N3904 Single Bipolar Transistor

Description

Tutorial: How to Use the Bipolar Transistor 2N3904

The NPN bipolar transistor 2N3904 is a fundamental component for electronic projects, ideal for amplification and switch control. It is particularly useful for beginners who want to learn the basics of transistor logic.

What you need

• amplification projects
• relay control
• current flow regulation
• basic circuit for Arduino projects

Steps

1. Check the polarity of the component: the actual pin ‘E’ (emitter) must be connected to the negative terminal of the power supply.
2. Connect the pin ‘B’ (base) to the Arduino digital pin for control.
3. Connect a load, such as a light bulb or relay, between the pin ‘C’ (collector) and the positive power supply.
4. Use the digitalWrite() function of Arduino to control the state of the transistor (HIGH = active, LOW = inactive).
5. Check the datasheet for the maximum base current value to avoid damaging the component.
6. If necessary, add pull-up or pull-down resistors to the base to improve circuit stability.
7. Test the functionality with a multimeter in continuity mode to verify if there is a connection between the ‘E’ and ‘C’ pins.
8. Modify the Arduino sketch by adding commands to test different input conditions.

Example code

void setup() {
  pinMode(2, OUTPUT);
}

void loop() {
  digitalWrite(2, HIGH); // Attiva il transistor
  delay(1000);
  digitalWrite(2, LOW); // Disattiva il transistor
  delay(1000);
}

Mini project

Create a simple LED control circuit with Arduino and the 2N3904 transistor. Connect the Arduino to a light bulb via the transistor to control its illumination.

Common mistakes

• Do not check the polarity of the pins
• Ignore the maximum current specifications in the datasheet
• Omit necessary base resistors
• Use a PNP transistor instead of an NPN

Recommended accessories

• Base resistor (1kΩ)
• Multimeter
• Arduino Uno
• 5V relay

Frequently asked questions

The transistor overheats during use.
Check if there are sufficient pull-up/pull-down resistors and that the maximum current specified in the datasheet has not been exceeded.

I can’t get the circuit to work with an LED.
Check the transistor connections, verify the power supply, and add a current-limiting resistor to the LED chain.

What are the main applications?
Audio amplification, relay control, current regulation for external devices.