21 Arduino Modules You Can Buy For Less Than $2

The Arduino community has created a wide variety of modules and shields that can enhance your projects. Here’s the ultimate collection of 21 Arduino Modules that you can get for less than $2 on eBay. Let’s start!

List of the Best 21 Arduino Modules

Sensors are awesome because they allow us to know what’s going on in the outside world. There are sensors for almost anything you can think of. In this guide we’re going to show you a collection of 21 Arduino sensors and modules you can buy for less than $2. We also have instructions on how to use most of them with the Arduino.

1. HC-SR04 Ultrasonic Module

The HC-SR04 ultrasonic sensor uses sonar to determine distance to an object like bats do. It offers excellent non-contact range detection with high accuracy and stable readings in an easy-to-use package. Here’s a complete guide on how to use this module. View this module on eBay ->

2. IR Infrared Obstacle Avoidance Sensor Module

This module is very easy to use and is often used in robots to detect objects near the sensor. These sensors have a digital output pin that outputs a signal when it detects an object. When the module detects an obstacle, the green indicator light on the board lights up. The module detects the distance 2 ~ 30cm, detection angle 35 °. View this module on eBay ->

3. Soil Hygrometer Detection Module Soil Moisture Sensor

This is a simple water sensor that can be used to detect soil moisture. It outputs a high signal when the moisture is above a certain threshold. You can also read an analog signal whose value is proportional to the moisture level. Use this sensor to create an automatic self-watering plant. Here’s the complete guide on how to use the hygrometer module with your Arduino. View this module on eBay ->

4. Microphone Sensor

This sensor is used for sound detection. This module has two outputs: AO (analog output), or DO (digital output). The digital output sends a high signal when the sound the sound intensity reaches a certain threshold. The threshold-sensitivity can be adjusted via potentiometer on the sensor. Learn how to use this sensor with our complete guide.  View this module on eBay ->

5. Digital Barometric Pressure Sensor Board

You can use this module to measure the absolute pressure of the environment. By converting the pressure measures into altitude, you have a reliable sensor for determining the height of your robot or projectile, for example. This sensor also measures temperature and humidity. Here’s the complete guide on how to use this sensor. View this module on eBay ->

6. Photoresistor Sensor Module Light Detection Light

You can use this module for light detection with an Arduino. For example, you can build a Night Security Light project. View this module on eBay ->

7. Digital Thermal Sensor Module Temperature Sensor Module

The thermal sensor module is very sensitive to the ambient temperature, generally used to detect the ambient temperature. Through the adjustment of the potentiometer, you can change the temperature detection threshold. View this module on eBay ->

8. Rotary Encoder Module Brick Sensor Development Board

When you rotate the rotary encoder it counts in the positive direction and the reverse direction. Rotation counts are not limited. With the buttons on the rotary encoder, you can reset to its initial state and start counting from 0. View this module on eBay ->

9. MQ-2Gas Sensor Module Smoke Methane Butane Detection

This sensor module utilizes an MQ-2 as the sensitive component and has a protection resistor and an adjustable resistor on board. The MQ-2 gas sensor is sensitive to LPG, i-butane, propane, methane, alcohol, Hydrogen and smoke. It could be used in gas leakage detecting equipments in family and industry. The resistance of the sensitive component changes as the concentration of the target gas changes. Here’s the complete guide on how to use the MQ-2 smoke sensor with the Arduino. View this module on eBay ->

10. SW-420 Motion Sensor Module Vibration Switch Alarm

This module can be used to trigger the effect of various vibration, theft alarm, intelligent car, earthquake alarm, motorcycle alarm, etc. View this module on eBay ->

11. Humidity and Rain Detection Sensor Module

This is a rain sensor. It’s used for all kinds of weather monitoring. Here’s the complete guide on how to use the rain sensor module with the Arduino. View this module on eBay ->

12. Passive Buzzer Module

A simple sound making module. You set high or low to drive this module. By changing the frequency you’ll hear a different sound. View this module on eBay ->

13. Speed Sensor Module

Tachometer is a simple module that allow you to test the speed of the motor. Widely used for motor speed detection, pulse count, position limit, and so on. View this module on eBay ->

14. IR Infrared Flame Detection Sensor Module

Flame detection sensor module is sensitive to the flame, but also can detect ordinary light. This is usually used as a flame alarm. Detects a flame or a light source of a wavelength in the range of 760nm to 1100 nm. Detection point of about 60 degrees, particularly sensitive to the flame spectrum. View this module on eBay ->

15. 5V 2-Channel Relay Module

This is a 2 Channel 5V Relay Module. It allows you to control various appliances that operate at high voltages, with low voltages like 5V. It can be controlled directly by any microcontroller. Here’s the complete guide on how to use the relay module with the Arduino. View this module on eBay ->

16. Breadboard Power Supply Module 3.3V 5V

A simple module to power your breadboard. It supplies both 3.3V and 5V. This is specially useful to power up your breadboard circuits from an external power supply. View this module on eBay ->

17. HC-SR501 Pyroelectric Infrared Sensor Module

A PIR sensor is a little module that allows you to detect movement from humans or pets. It’s easy to integrate with your microcontroller. You can learn here how to use this module with an Arduino. View this module on eBay ->

18. Accelerometer Module

This module measures the acceleration. It’s commonly used in portable devices and video game controllers to detect movement and actions from the player. View this module on eBay ->

19. DHT11 Temperature and Humidity Sensor

It’s a great little sensor to measure temperature and humidity in your room or outside. It integrates seamlessly with the Arduino. You can learn here how to use this module in your project. View this module on eBay ->

20 or 21. RF 433MHz Transmitter/Receiver

If you need data sent from one microcontroller to another, the 433MHz link modules are a cheap way to do that (all data is sent via Radio Frequency). Here’s the complete guide on how to use the 433MHz transmitter and receiver with the Arduino. View this module on eBay ->

[Extra] ESP8266 WiFi Module ($4)

This module costs a little bit more than $2, but it’s totally worth it. You can get one ESP8266 WiFi Module for about $4 on eBay. This module can send emails, host a web server, control LEDs, etc. If you are curious about this module check out my eBook Home Automation Using ESP8266.

Get an Arduino Sensors and Modules Kit

Instead of getting each module separately, there are a wide variety of kits with different Arduino sensors and modules. Getting one of these kits is a great way to get started with your Arduino. Find the best Arduino Sensors and Modules Kits on our blog post.

Need Tutorials to Get Started?

Do you have an Arduino sensor or module and you don’t know how to use it? We have instructions on how to use up to 23 Arduino sensors and modules in our Ultimate Guide For Arduino Sensors/Modules eBook. This guide is completely free and provides schematics, code, and examples on how to use your sensors with the Arduino. Click here to get access to the eBook.

If you are an absolute beginner in the Arduino world, we recommend you following our FREE Arduino Mini Course first, that you can get access here.

Wrapping Up

Do you have all these modules? Are you thinking about ordering one of theses modules listed above?

Leave a comment down below!

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You may also like the following resources:

• Best Arduino Sensors and Modules Kits
• Best Aduino Starter Kits
• Arduino Step-by-step projects course

Thanks for reading.