Lesson 16 Magic Cup

Introduction

There are two same Magic Cup modules in this kit, and each adds a separate LED based on the mercury switch. You may learn the application of one module and then try to apply two modules together to make one dim when at the same time the other brightens.

Components

– 1 * Raspberry Pi

– 1 * Breadboard

– 1 * Network cable (or USB wireless network adapter)

– 2 * Magic cup module

– Several jumper wires

Experimental Principle

Tilt the module and the LED onside will dim gradually. The working principle is similar to that of the Mercury Switch.

Experimental Procedures

Step 1: Build the circuit

                  Magic Cup                               Raspberry Pi

                     L ———————————— GPIO1

                     S ———————————— GPIO0

                     + ———————————— 3.3V

                     G ———————————— GND

Step 2: Edit and save the code (see path/Rpi_SensorKit_code/29_magicCup/magic.c)

Step 3: Compile

              gcc  magic.c  -lwiringPi

Step 4: Run

              ./a.out

Now, tilt the magic cup and the LED on one module will get dim.

 magic.c

#include <wiringPi.h>
#include <stdio.h>

#define   SIG   0
#define   LED   1

int main(void)
{
	if(wiringPiSetup() == -1){
		printf("setup wiringPi failed !");
		return 1; 
	}
	
	pinMode(SIG, INPUT);
	pinMode(LED, OUTPUT);

	while(1){
		if(0 == digitalRead(SIG)){
			digitalWrite(LED, 1);	
		}		
		else{
			digitalWrite(LED, 0);	
		}
	}

	return 0;
}

Python Code

#!/usr/bin/env python

import RPi.GPIO as GPIO
import time

MERCURY_SIG1 = 11
LED1 = 12

LED2 = 15


def setup():
	global p_LED1, p_LED2
	GPIO.setmode(GPIO.BOARD)
	GPIO.setup(MERCURY_SIG1, GPIO.IN)
	GPIO.setup(LED1, GPIO.OUT)
	GPIO.setup(LED2, GPIO.OUT)

	p_LED1 = GPIO.PWM(LED1, 200)
	p_LED2 = GPIO.PWM(LED2, 200)
	
	p_LED1.start(0)
	p_LED2.start(0)
	
def loop():
	led1_value = 0
	led2_value = 0
	while True:
		mercury_value = GPIO.input(MERCURY_SIG1)
		if mercury_value == 0:
			led1_value -= 1
			led2_value += 1
			if led1_value < 0:
				led1_value = 0
			if led2_value > 100:
				led2_value = 100
		
		if mercury_value == 1:
			led1_value += 1
			led2_value -= 1
			if led1_value > 100:
				led1_value = 100
			if led2_value < 0:
				led2_value = 0
				
		p_LED1.ChangeDutyCycle(led1_value)
		p_LED2.ChangeDutyCycle(led2_value)
		time.sleep(0.05)
		
def destroy():
	p_LED1.stop()
	p_LED2.stop()
	GPIO.cleanup()
	
if __name__ == "__main__":
	try:
		setup()
		loop()
	except KeyboardInterrupt:
		destroy()