Exercise 3: Switches

Introduction

Switches exist in various incarnations. There are the simple mechanical switches: on/off or push button switches but there are also switches than turn on or off with various external conditions:

• temperature
• infra red radiation (e.g. the Passive Infrared Sensor or PIR sensor)
• Hall switches detecting magnetic field
• microphone switches which turn on when a certain noise level is detected

and a PIR sensor.

Exercise 1:

The push button switch is connected to GPIO 17 on the ESP32 board.

Write a script that polls the state of the switch every 100 ms and prints state changes (only print out a message when the switch state has changed). Catch <ctrl> C to smoothly exit the program.

Check https://docs.micropython.org/en/latest/esp8266/tutorial/pins.html and https://docs.micropython.org/en/latest/esp32/quickref.html for information on how to accomplish this.

Exercise 2:

Do the same thing as in exercise 1 but use external interrupts and a callback routine to do the job.

Exercise 3:

Combine this exercise with the exercise on LEDs: Switch the builtin LED on when the button is pressed and off when it is released

Exercise 4:

Write a program scanning the PIR sensor, indicating if a person is close. The PIR sensor, just like the push button, uses a single GPIO line as input. The boards allows to choose which GPIO to use and I selected D4 = GPIO 16

Exercise 5:

The sensor kit in the lab contains a big number of sensors acting like switches:

• rolling ball switch
• mercury switch
• noise level detector (microphone)
• hall sensor (detecting magnetic field)
• reed relay (detecting magnetic field)
• and many more...

-- Uli Raich - 2020-05-06

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