Workshop 3: Program Flow

: Using the embedded controller to produce a programmed output (LED indication and sound) basic on the inputs.

Objective: This workshop is designed to familiarize the student with elements of the embedded microcontroller.

Real-World Application: Home security system.


1. Hardware:

2. PBasic Software Commands



Mount the LEDs vertically on the photoboard with the three red LEDs on top and the green on the bottom. Using a DIP switch as door inputs, program a security system that checks the back door, front door and basement doors locked. When the door is shut and locked the input to the Pic is a logic high and the corresponding red LED is lit, if the door is open then the input is a logic low and the corresponding red LED is off. When all the doors are shut the program flashes the red LEDs on and off for five seconds, leaving them off and lights the green LED. The system continuously monitors the door inputs, if any door is opened the green LED goes off, an audible alarm is sound and light the corresponding red LED is lit. Enable and disable the system using the Pic reset (via DIP switch).

Hint: To prevent false alarms at start up the program should verify all doors are lock prior to going into the monitoring mode.

Circuit Drawing for Workshop # 3

PicBasic Code for Workshop #3

setup:   low 4: low 5: low 6
start:    b4 = pin0                           'read pin 0 - check front door
           b0 = b4& %00000001         'clear all bits except bit 1put into b0
           if b0 = %00000001 then lock_1_is_set                 'jump if front door is locked
           goto start                           'recheck front door
check2: b5 = pin1                          'read pin 1 - check back door
             b1 = b5&%00000001    'clear all bits except bit 1put into b1
             if b1 = %00000001 then lock_2_is_set          'jump if back door is locked
            goto check2                      'recheck back door
check3: b6 = pin2                          'read pin 2 - basement door
             b2 = b6&%00000001    'clear all bits except bit 1put into b2
            if b1 = %00000001 then lock_3_is_set          'jump if basement is locked
            goto check3                       'recheck basement door
            high 4                               'front door is locked light LED
            goto check2                      'now check back door
           high 5                               'back door is locked light LED
           goto check3                      'now check basement door
          high 6                                'basement door is locked light LED
alarm_is_set:                               'flashes LEDs to signal that the doors
                                              'are locked and the alarm is set
         for b7=1 to 10
               toggle 7 :toggle 6 : toggle 7: pause 500
         next b7
         low 4                                  'turn off back door LED
         low 5                                  'turn off front door LED
         low 6                                  'turn off basement door LED
         high 7                                'turn on system set LED
check_doors:                              'final check before setting alarm
        if b8 = %00000111 then monitor_doors
        goto setup
       b9=pins                               'read all pins into b9
       b8=b9&%00000111              'clear all bits except first three (doors)
       if b8 <>%00000111 then intruder_alarm
                                             'if door(s) are unlocked sound alarm
goto monitor_doors
                                             'recheck doors
intruder_alarm:                           'lights the red LED for the door that has been
                                            'opened, creates alarm tone on speaker and
                                            'turns off green LED
       low7: b1=0: b2=0
       if b8=%00000110 then lit_front
       if b8=%00000101 then lit_back
             if b8=%00000011 then lit_basement
       goto sounds
lit_front: low 4
      goto sounds
lit_back: low 5
      goto sounds
lit_basement: low 6

sounds: for b1=1 to 21 step 5
     b2= b1 * 10
    sound 3,(b1,20,b2,40)
    pause 100
    next b1
    goto setup