Breadboard Transistor On-Off Switch

Electronics

Published

January 25, 2020

Modified

January 25, 2020

Setup on a breadboard

List or required components:

Pcs.	Description
2	NPN transistor (e.g PN2222A)
2	LED
4	Resistor (e.g. 560Ω)
2	Push Button (e.g. COM-00097)
1	Breadboard including wires

Transistor Circuit

The base-emitter voltage of both transistors is controlled by push buttons. The on switch in the middle lights the LED if the button is pressed (enabling the A input):

Truth table (logic level “1” HIGH, and “0” LOW)

A	Q
0	0
1	1

The left circuit switches the LED off if the button is pressed. This is called an inverter, an represents the function of a logic NOT gate:

A	Q
0	1
1	0

The output Q from a NOT gate only return HIGH if the input is a logic level LOW.

---
title: Breadboard Transistor On-Off Switch
categories:
  - Electronics
date: 2020/01/25
date-modified: 2020/01/25
---

![Setup on a breadboard](breadboard_transistor_switch/breadboard.png)

List or required components:

| Pcs. | Description                  |
|------|------------------------------|
| 2    | NPN transistor (e.g PN2222A) |
| 2    | LED                          |
| 4    | Resistor  (e.g. 560Ω)        |
| 2    | Push Button (e.g. COM-00097) |
| 1    | Breadboard including wires   |


![Transistor Circuit](breadboard_transistor_switch/schematic.png)

The base-emitter voltage of both transistors is controlled by push buttons. The on switch in the middle lights the LED if the button is pressed (enabling the A input):

Truth table (logic level "1" HIGH, and "0" LOW)

| A | Q |
|---|---|
| 0 | 0 |
| 1 | 1 |

The left circuit switches the LED off if the button is pressed. This is called an **inverter**, an represents the function of a **logic NOT gate**:

| A | Q |
|---|---|
| 0 | 1 |
| 1 | 0 |

The output Q from a NOT gate only return HIGH if the input is a logic level LOW.