Bx24 Debounce Example

Physical Computing: Jen Lewin 2002

Step One: Setup a version of "Flashme" for your BX

Flashme is a very simple startup function I wrote for my BX. "Flashme" is the first things I run for every program I write on the BX. This helps by providing useful startup information, that often saves me great time in debugging.

Sub Main()

call flashme(5)
'I place my new function (defined below) flashme, as the first thing to run on the BX. This function passes the number 2... in the function definition below... this number... will equal my variable "flashX".

End Sub

sub flashme(byVal flashx as byte)
'create a function called "flashme", with one passed byte variable (passed by its value) called "flashX"

dim x as byte 'create a byte variable (just for inside this flashme function) called X
debug.print"RESTART" 'this prints the text "RESTART" to the com window..Sometimes your chip will turn off without your knowing it... the "restart" text, like the flash sequence below, is simply an indicator to let us know when our chip may have been shutdown.

             for x = 0 to flashx 'flash pin 25 on and off flashX times...for example, if flashX = 5, it will flash 5 times
               call putpin(25, 0)
               delay(0.1)
               call putpin(25, 1)
               delay(0.1)
             next

       call putpin(26, 0) 'once everything is finished, turn pin 26 (the green 'go' pin on)
end sub

STEP TWO: Simple Switches

Wire up a simple switch to your BX pin 12.

Run the following script on your BX

sub Main()

do

debug.print"my pin 12 switch is ", cstr(getpin(12))
delay(0.2)

loop

end sub

Simple Switch Schematic:

In your com port window, you should see the value of your switch( 1's for on, 0's for off.)
Now imagine your were creating a musical instrument where each time you push the switch you want to hear a tone. In the above example, If you were to hold down the switch, the tone would continue to play (in the com port you would be seeing a 1 , 1, 1, 1 and in your instrument you would be hearing tone, tone, tone, tone).

Most instruments, and in general most switches do not work this way. When we pluck a string, it resonates only once (until we pluck again). Likewise, most switches only "do something" once when pushed, not continually while they are pushed.

In the below example, I have created a program that only "does something" (in this case, it only prints the value of the switch to the com window), one time (for each switch press).

Write your own similar example (perhaps even as a separate function like "flashme" ).

'SET UP VARIABLES

dim mySwitch as byte 'create a variable called mySwitch that is a byte
dim switchON as byte 'create a variable called switchON that is a byte

sub main()

call flashme(5) 'see example above

'set up the default values for my variables
mySwitch = 0
switchON = 0

DO

        if getPin(12) = 1 then                  'if the switch is on....
                     if switchON = 1 then      'then if it is on, AND if it is being held down (if it was already pressed)
                                  'do nothing
                     else                                            'if it is ON, but not already pressed
                          mySwitch = mySwitch + 1            'add 1 to mySwitch
                          switchON = 1                              'set switchON to be 1
                          debug.print cStr(mySwitch)           'print the value of switchON
                      end if
         else 'Switch is not on
             switchON = 0 'is if the switch is not on, set the value of SwitchON to 0
         end if

loop

end sub