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2.1 Button

Introduction

In this project, we will learn how to use a button to control an LED. Buttons are fundamental input devices used in various electronic projects to interact with circuits and systems.

What You’ll Need

To complete this project, you will need the following components:

COMPONENT	PURCHASE LINK
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
LED	BUY
Button	BUY
Fusion HAT+	-
Raspberry Pi	-

Circuit Diagram

We will use a normally open button as an input for the Raspberry Pi. When the button is pressed, GPIO17 will receive a high-level signal (3.3V). The Raspberry Pi will detect this signal and turn the LED on. The circuit connections are shown in the diagrams below:

Wiring Diagram

Follow these steps to build the circuit:

Connect the anode (long pin) of the LED to a GPIO pin (GPIO22) through a current-limiting resistor.
Connect the cathode (short pin) of the LED to the ground (GND).
Connect one terminal of the button to GPIO17 and the other terminal to the ground (GND).

Running the Example

All example code used in this tutorial is available in the ai-lab-kit directory. Follow these steps to run the example:

cd ~/ai-lab-kit/python/
sudo python3 2.1_Button.py

This Python script demonstrates an interactive setup where a button controls an LED. When executed:

Pressing the button (connected to GPIO pin 17) turns the LED (connected to GPIO pin 22) on.
Releasing the button turns the LED off.
The program runs indefinitely, listening for button press and release events to control the LED.

Code

The following Python code toggles the LED based on button presses and releases:

#!/usr/bin/env python3
from fusion_hat.pin import Pin, Mode, Pull
from signal import pause  # Import pause function from signal module

# Initialize an LED object on GPIO pin 22
led = Pin(22,mode=Mode.OUT)
# Initialize a Button object on GPIO pin 17
button = Pin(17, mode=Mode.IN, pull=Pull.DOWN)

# # Link the button's "when_activated" event to the LED's high() method
button.when_activated = led.high

# # Link the button's "when_deactivated" event to the LED's low() method
button.when_deactivated = led.low

# Run an event loop that waits for button events and keeps the script running
print("CTRL + C to exit")
pause()

Understanding the Code

Library Import

The fusion_hat library provides a simple interface for GPIO control, and the signal module is used to keep the program running.

#!/usr/bin/env python3
from fusion_hat.pin import Pin, Mode, Pull
from signal import pause  # Import pause function from signal module

Component Initialization

The LED is connected to GPIO pin 22, and the Button is connected to GPIO pin 17.

# Initialize an LED object on GPIO pin 22
led = Pin(22,mode=Mode.OUT)
# Initialize a Button object on GPIO pin 17
button = Pin(17, mode=Mode.IN, pull=Pull.DOWN)

Event Handling

The when_activated and when_deactivated events are linked to the LED’s high() and low() methods, respectively. This ensures that the LED turns on when the button is pressed and off when the button is released.
```
button.when_activated = led.high
button.when_deactivated = led.low
```
Event Loop

The pause() function keeps the program running and listens for button press and release events.
```
pause()
```

Troubleshooting

LED Does Not Light Up
- Cause: Incorrect GPIO pin connection or LED wiring.
- Solution: Verify that the LED’s positive leg is connected to GPIO pin 22 and its negative leg to a resistor leading to ground.
Button Press Has No Effect
- Cause: Incorrect button wiring or GPIO pin configuration.
- Solution: Ensure the button is connected correctly to GPIO pin 17 and ground. .
LED Stays On or Off Regardless of Button State
- Cause: The button may not trigger events correctly.
- Solution: Check the button’s functionality by directly testing its connectivity with a multimeter or simple circuit.

Extendable Ideas

Toggle LED State

Modify the script to toggle the LED’s state with each button press instead of turning it on/off directly:

def toggle():
   if led.value() == 1:
      led.off()
   else:
      led.on()

button.when_activated = toggle

Multiple LEDs

Control multiple LEDs with a single button, cycling through different patterns:

leds = [LED(17), LED(27), LED(22)]
current_led = 0

def cycle_leds():
   global current_led
   leds[current_led].off()
   current_led = (current_led + 1) % len(leds)
   leds[current_led].on()

button.when_activated = cycle_leds

Button Press Duration

Add functionality to perform different actions based on how long the button is held:

from time import time

press_time = None

def start_timer():
   global press_time
   press_time = time()

def check_duration():
   global press_time
   duration = time() - press_time
   if duration < 2:
      led.on()
   else:
      led.off()

button.when_activated = start_timer
button.when_deactivated = check_duration

Debouncing

Implement software debouncing for more accurate button press detection:

from time import time

press_time = None
debounce_time = 0.2

def press():
   global press_time
   press_time = time()

def debounce():
   global press_time
   current_time = time()
   duration = current_time - press_time
   if duration < debounce_time:
      return
   else:
      led.on()

button.when_activated = press
button.when_deactivated = debounce

Conclusion

This project demonstrates how to use a button to control an LED with a Fusion HAT+. Buttons are versatile components and can be integrated into various applications, from basic circuits to complex interactive systems.