5.6 Two Kinds of Transistors

This kit is equipped with two types of transistors, S8550 and S8050, the former is PNP and the latter is NPN. They look very similar, and we need to check carefully to see their labels. When a High level signal goes through an NPN transistor, it is energized. But a PNP one needs a Low level signal to manage it. Both types of transistor are frequently used for contactless switches, just like in this experiment.

Let’s use LED and button to understand how to use transistor!

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name

ITEMS IN THIS KIT

LINK

ESP32 Starter Kit

320+

ESP32 Starter Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION

PURCHASE LINK

ESP32 WROOM 32E

BUY

ESP32 Camera Extension

-

Breadboard

BUY

Jumper Wires

BUY

Resistor

BUY

LED

BUY

Button

BUY

Transistor

BUY

Available Pins

  • Available Pins

    Here is a list of available pins on the ESP32 board for this project.

    For Input

    IO14, IO25, I35, I34, I39, I36, IO18, IO19, IO21, IO22, IO23

    For Output

    IO13, IO12, IO14, IO27, IO26, IO25, IO33, IO32, IO15, IO2, IO0, IO4, IO5, IO18, IO19, IO21, IO22, IO23

  • Conditional Usage Pins (Input)

    The following pins have built-in pull-up or pull-down resistors, so external resistors are not required when using them as input pins:

    Conditional Usage Pins

    Description

    IO13, IO15, IO2, IO4

    Pulling up with a 47K resistor defaults the value to high.

    IO27, IO26, IO33

    Pulling up with a 4.7K resistor defaults the value to high.

    IO32

    Pulling down with a 1K resistor defaults the value to low.

  • Strapping Pins (Input)

    Strapping pins are a special set of pins that are used to determine specific boot modes during device startup (i.e., power-on reset).

    Strapping Pins

    IO5, IO0, IO2, IO12, IO15

    Generally, it is not recommended to use them as input pins. If you wish to use these pins, consider the potential impact on the booting process. For more details, please refer to the Strapping Pins section.

Way to connect NPN (S8050) transistor

../../_images/circuit_5.6_S8050.png

In this circuit, when the button is pressed, IO14 is high.

By programming IO26 to output high, after a 1k current limiting resistor (to protect the transistor), the S8050 (NPN transistor) is allowed to conduct, thus allowing the LED to light up.

../../_images/5.6_s8050_bb.png

Way to connect PNP(S8550) transistor

../../_images/circuit_5.6_S8550.png

In this circuit, IO14 is low by the default and will change to high when the button is pressed.

By programming IO26 to output low, after a 1k current limiting resistor (to protect the transistor), the S8550 (PNP transistor) is allowed to conduct, thus allowing the LED to light up.

The only difference you will notice between this circuit and the previous one is that in the previous circuit the cathode of the LED is connected to the collector of the S8050 (NPN transistor), while this one is connected to the emitter of the S8550 (PNP transistor).

../../_images/5.6_s8550_bb.png

Code

Note

  • You can open the file 5.6_transistor.ino under the path of esp32-starter-kit-main\c\codes\5.6_transistor.

  • After selecting the board (ESP32 Dev Module) and the appropriate port, click the Upload button.

  • Always displaying “Unknown COMxx”?

Two types of transistors can be controlled using the same code. When we press the button, the ESP32 will send a high-level signal to the transistor; when we release it, it will send a low-level signal.

  • The circuit using the S8050 (NPN transistor) will light up when the button is pressed, indicating that it is in a high-level conduction state;

  • The circuit using the S8550 (PNP transistor) will light up when the button is released, indicating that it is in a low-level conduction state.