Tom's Main Menu

Physical Computing Home

Intro to Physical Computing Syllabus

Networked Objects

Sustainable Practices

blog

Resources

code, circuits, & construction

my del.icio.us links

 

Lab Assignment

  
Digital Input and output using the microcontroller  

Minimum parts needed: (new parts in bold. see parts list for details)

  • Prototyping board (breadboard)
  • Power supply connector
  • 5-15VDC power supply
  • Assorted wires
  • 5V regulator
  • PIC 18F452 or BX-24
  • Serial cable
  • DB9 female serial connector & headers
  • 4MHZ crystal for PIC
  • 22pF capacitors for crystal
  • LED's
  • Switches
  • 10Kohm resistors
  • 220 ohm resistors

Step 1:

Connect an LED and a 220 ohm resistor in series with each of the eight pins on your microcontroller (5 to 12 on a BX-24, portd.0 to portd.7 on a PIC 18F452). Connect the end of the LED to ground.
LED out on portd.1 of a PIC 18F452
LED out on pin 12 of a BX-24

Program the microcontroller to light up each LED with a pause in between.

BX-24:

Sub main()
	call delay(0.5)  ' start  program with a half-second delay 

	do
		call putPin(12, 1)
		call delay(0.5)
		call putPin(12,0)
		call putPin(13,1)
		call delay(0.5)
		' fill in the rest of the pins yourself
	loop
end sub

PicBasic Pro:

main:
	high portd.0
	pause 500
	low portd.0
	high portd.1
	pause 500
	' fill in the rest of the pins yourself
goto main
 
Step 2:

Connect a switch (or several switches) any of pins of your microcontroller:
switch on portb.0 of a PIC 18F452
switch on pin 13 of a BX-24

Connect an LED to another pin as shown above, and program the microcontroller to change the LED when the switch changes. Here's one possibility:

BX-24:

sub main()
	do
		if getPin(13) = 1 then	' if the switch is closed on pin 13
			call putPin(12,0)	' set pin 12 low
		else
			call putPin(12,1)	' set pin 12 high

		end if
	loop
end sub

PicBasic Pro:

input portb.0 
output portd.1

main: 
	if portb.0 = 1 then ' if the switch is closed on pin RB0
		low portd.1 ' set pin RD1 low
	else
		high portd.1	' set RD1 high 
	endif 
goto main
  
Step 3:

Combine switches and LED's to make a more complex application. Make a puzzle or a combination lock using your switches. Use the LED's to give the user visual feedback. Or think about incorporating ripple effects, where one switch affects many outputs.

Besides the progamming and electronic aspects of your application, consider also the material aspects. What is the ideal switch for your application? Will a standard switch work, or will you need something special, like a whisker switch or a tilt switch or a magnetic switch? Will you need to build your own switch? Will you need to build it into a structure so that the user doesn't realize she's triggering action, or should it be a clear, unambiguous controller?

Feel free to incorporate any additional elements from future labs or other sources in your application.