Electronics Cookbook

Chapter 12. Sensors

12.0 Introduction

This chapter looks at sensors that convert some physical measurement such as temperature, light, or physical movement into an analog or digital electronic signal.

Many different sensors are explained, and where appropriate, ways of using them with an Arduino or Raspberry Pi are included.

12.1 Connect a Switch to an Arduino or Raspberry Pi

Problem

You want to be able to convert a mechanical movement to a digital on/off signal that you can use with an Arduino or Raspberry Pi.

Solution

Connect the switch between GND and a GPIO pin set to be a digital input as shown in Figure 12-1 and enable the GPIO pin’s internal pull-up resistor.

Figure 12-1. Connecting a Switch to a GPIO Pin

Your software will probably also need to “debounce” the signal from the switch.

Contact Bounce

It’s tempting to think that when you press a push switch or flip a toggle switch the contacts will instantly close in one single action and a GPIO input connected to the switch will instantly change from high to low (assuming the situation of Figure 12-1).

In reality, switch contacts will often bounce as the switch is pressed, and a button press might make several transitions between high and low as it is pressed, before settling.

Figure 12-2 shows the oscilloscope (Recipe 21.9) trace for a particularly bouncy button. The horizontal axis is time and you can see several ...