Component Wiring

This section illustrates the physical connections to the Raspberry Pi's GPIO pins. The rope pull sensor (a simple button) is connected to an input pin and ground. The speaker connects to the audio jack. Power from your solar circuit connects to the 5V and Ground pins. Hover over a pin for its label.

Software Setup & Script

First, prepare your Raspberry Pi by installing the necessary software. Open a terminal and run these commands:

sudo apt update && sudo apt upgrade -y
sudo apt install python3-pip -y
pip3 install RPi.GPIO pygame

Next, save the following Python code as a file named `whistle.py` on your Raspberry Pi. Make sure you also have a sound file named `train_whistle.wav` in the same directory.

import RPi.GPIO as GPIO
import pygame.mixer
import time

BUTTON_PIN = 17
SOUND_FILE = "train_whistle.wav"

def button_callback(channel):
    print("Button pressed!")
    if not pygame.mixer.get_busy():
        pygame.mixer.Sound(SOUND_FILE).play()

GPIO.setmode(GPIO.BCM)
GPIO.setup(BUTTON_PIN, GPIO.IN, pull_up_down=GPIO.PUD_UP)
pygame.mixer.init()

GPIO.add_event_detect(BUTTON_PIN, GPIO.FALLING, callback=button_callback, bouncetime=300)

print("Train whistle machine is running. Press Ctrl+C to exit.")

try:
    while True:
        time.sleep(1)
except KeyboardInterrupt:
    print("Exiting.")
finally:
    GPIO.cleanup()

Run the script from your terminal:

python3 whistle.py

How It All Works

The entire system operates in a simple, continuous loop, waiting for interaction. This walkthrough explains the end-to-end process from capturing sunlight to making sound.

1. Solar Charging: The solar panel converts sunlight into electricity. This power is fed into the charge controller, which safely manages the charging of the battery pack, preventing overcharging and ensuring a stable power reserve.
2. Powering the Pi: The battery provides stored power. When the sun isn't out, the battery ensures the system stays online. A DC-DC boost converter steps up the battery's voltage to the stable 5V required by the Raspberry Pi.
3. Waiting for a Signal: The Python script runs continuously on the Raspberry Pi. It configures GPIO pin 17 as an input with a "pull-up resistor". This means the pin's state is normally HIGH (on).
4. Rope Pull Detection: When the rope is pulled, it presses the button. This connects GPIO 17 to a Ground pin, causing its state to switch from HIGH to LOW (off). This change is called a "falling edge".
5. Python Script Action: The script is programmed to detect this specific "falling edge" event on GPIO 17. When it does, it immediately triggers the `button_callback` function.
6. Sound Playback: Inside the callback function, the `pygame` library is instructed to load and play the `train_whistle.wav` file. The sound is then output through the Raspberry Pi's audio jack to the connected speaker.