Follow Us

This week Bob shows us his real world project to monitor activity in a room to turn on a light using a Raspberry Pi.

 

Downloads

HD   Apple HD   Apple SD   Audio MP3

 

Segment 1

Segment 1

#!/usr/bin/python

import math
import time
import RPi.GPIO as GPIO

global TRIGPIN
global ECHOPIN
global RELAY1PIN
# Pin numbers are based on functions,
# not physical pins.
TRIGPIN = 25     # physical pin 22
ECHOPIN = 24     # physical pin 18 
RELAY1PIN = 23   # physical pin 16

global DEBUG
DEBUG = True


def readHCSR04():
    
    # Disable warning
    GPIO.setwarnings(False)
    GPIO.setmode(GPIO.BCM)
    
    distance = 0
    
    # Setup Trig pin, and turn it off
    GPIO.setup(TRIGPIN,GPIO.OUT)
    GPIO.output(TRIGPIN,GPIO.LOW)

    # Setup Echo pin
    GPIO.setup(ECHOPIN,GPIO.IN)
    
    # Turn on Trig pin for 10 microseconds, then turn it off
    GPIO.output(TRIGPIN, True)
    time.sleep(0.00001)
    GPIO.output(TRIGPIN, False)

    # Listen to the input pin and wait for the pin to go high.
    #==========================================================
    # The signalOff keeps being reset until the pin goes high
    startTime = time.time()
    signalOff = 0
    while (GPIO.input(ECHOPIN) == 0 and distance == 0):
      signalOff = time.time()
      elapsedTime = signalOff - startTime
      if elapsedTime > 1: 
        distance = 999
    
    # The signalOn keeps being reset until the pin goes low.
    startTime = time.time()
    signalOn = 0
    while (GPIO.input(ECHOPIN) == 1 and distance == 0):
      signalOn = time.time()
      elapsedTime = signalOn - startTime
      if elapsedTime > 1: 
        distance = 998
   
    # Calculate the time the pin was on
    if (distance == 0):
        timeOn = signalOn - signalOff 
        if (DEBUG == True):
            buffer = 'timeOn = ' + repr(timeOn)
            print buffer
        
        # convert the time in seconds to cm or inches
        # speed of sound is approx. 34000 cm/sec
        # speed of sound is approx. 13500 inch/sec
        # The value must be divided by 2 because we only need the 
        # return value.  The timeOn includes the time it takes to 
        # get to the surface in addition to the time it took to return.
        tempDistance = timeOn * (34000/2)

        # round to 2 significant digits
        distance = math.ceil(tempDistance * 100) / 100

    GPIO.cleanup()

    # return the distance, or the error code
    return distance
    
#end of readHCSR04()



# 
#  Loop through reading the sensor forever
#
count = 0
errors = 0
beginTime = time.time()
timeNow = time.time()
startingTime = time.strftime("%c")
GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)
GPIO.setup(23,GPIO.OUT)
GPIO.output(23,GPIO.HIGH)
whileLoop = True

while (whileLoop == True): 
    try:
        count += 1
        sensorReading = readHCSR04()

        if (sensorReading == 0) or (sensorReading == 998) or (sensorReading == 999):
            errors += 1
        
        if (DEBUG == True):
            buffer = 'Sensor reading ' + repr(count) + ' = ' + repr(sensorReading) + 'cm'   
            print buffer
            buffer = 'Error count = ' + repr(errors)
            print buffer
            
        GPIO.setwarnings(False)
        GPIO.setmode(GPIO.BCM)
        GPIO.setup(RELAY1PIN,GPIO.OUT)

        # if the sensor reads something within
        # 10cm, then turn on the light
        if (sensorReading <= 10) and (sensorReading >= 0.1):
            GPIO.output(RELAY1PIN,GPIO.LOW)
            beginTime = time.time()
            if (DEBUG == True):
                print 'Valid Reading'

        timeNow = time.time()
        elapsedTime = math.ceil((timeNow - beginTime) * 100) / 100
        if (DEBUG == True):
            buffer = 'elapsedTime = ' + repr(elapsedTime) + ' sec'
            print buffer

        # if time is greater than 10 seconds,
        # turn off the light
        if (elapsedTime > 10):
            GPIO.output(RELAY1PIN,GPIO.HIGH)
            if (DEBUG == True):
                buffer = 'Time has expired on lightOn cycle ' #+ repr(lightOn)
                print buffer
    
        # Wait 1 sec and start the loop over
        time.sleep(1)
        
    # capture interrupt nicely for a clean exit from program   
    except KeyboardInterrupt:
       whileLoop = False


# this code isn't reached until the program is exiting
GPIO.output(RELAY1PIN,GPIO.HIGH)        
GPIO.cleanup()
print ''
print ''
print 'Summary:'
print '========'
buffer = 'Starting Time = ' + repr(startingTime)
print buffer
buffer = 'Total count = ' + repr(count)
print buffer
buffer = 'Total errors = ' + repr(errors)
print buffer
endingTime = time.strftime("%c")
buffer = 'Ending Time: ' + repr(endingTime)
print buffer

 

Twitter - Home