Digital Display

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Chapter 6

• Digital Display

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Every-Day Digital Display

• Digital displays are found on many devices, one
  being a microwave oven timer. Each of the 3
  digits is a 7-segment display controlled by a
  microcontroller.

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What's A 7-Segment Display?

• A 7-segment display is a package with 7
  bar-shaped LEDs arranged to allow the display of
  many useful digits and some letters.
• Each segment (labeled A-G) contains an LED which
  may be individually controlled. DP is an eighth
  LED, the decimal point.

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• Common cathode means that each segment's cathode
  is connected to common pins 3 8, allowing the
  anode of each to be connected to the
  controller.Only one of these two pins will need
  to be connected to vss.

Another version is the common anode. To the
right is a common cathode
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• By supplying anodes with Vdd, individual segments
  can be energized.

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Activity 1 Building and Testing the 7 Segment
display

• Build the circuit to the left with power off
• Turn power on and verify that segment A is now lit

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• Now modify your circuit so segment B lights up
• Use the circuit diagram to the left for reference
• Repeat this procedure to check all remaining
  segments on the display including the decimal
  point

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• Displaying the number 3 by setting up the circuit
  below
• What segments would be lit to display the number
  2 and the letter A? Now Try it!

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Activity 2 Controlling the Display

• Of course the BASIC Stamp can control Vdd to the
  segments from the I/O pins. Start by
  constructing the circuit below

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Programming the 7-Segment Display

• Enter, Run, and Save the code to the left
• Verify that each segment lights briefly
• Make a list that tells you which bs2 pin controls
  which segment on the display

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Your Turn

• Comment low pincounter
• What effect should this have?
• Try it!!

Each segment should remain lit after it is
activatedright?
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Activity 3 Displaying Digits

• The HIGH and LOW instructions could be used to
  control the display for digits 0-9 by energizing
  the required segments, but it would require a
  considerable amount of code.
• Try displaying the number three again, but this
  time make the basic stamp do it.

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All of this for one digit
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Displaying digits with less code

• DIRH OUTH OR DIRL OUTL are internal variable
  locations (registers) which can be used to
  control a single I/O pin or all I/O pins
  simultaneously. This allows a single line of
  code to display a unique digit.

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Two variables controlling 8 pins at once

• OUTH
• Refers to the output condition (5V or 0 Vthat is
  1 or 0) for the top 8 pins15 8 in that order
• SYNTAX
• OUTH 00000000
• This would set all 8 pins to output 0 volts or
  respond to inputs of 0 volts
• OUTH 11111111
• This tells the pins to output 5 Volts or respond
  to 5V inputs

• DIRH
• Refers to the directionthat is input (0) or
  output(1)
• SYNTAX
• DIRH 11111111
• This would tell all 8 pins to act as outputs, not
  inputs
• DIR 00000000
• This tells the pins to act as input pins, not
  output pins

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To make sense of the outh commands, it is often
convenient to view the circuit upside down
This command would make a 3 appear
OUTH 11010110
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Lets use these registers to create the number
three againTRY IT!!

• Very helpful when deciding how to turn on
  specific segments
• Set output condition of top 8 pins to 0 volts
• Direct 8 top pins to behave as output pins
• These two commands clear the display
• Light specific segments to create the number 3

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Enter, Run and Save the code on the next slide (
page 177 of your text.)

• Verify that the decimal digits 0 through 9 are
  displayed

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How DisplayDigits.bs2 works

• Tells pins 8 15 to output 0 Volts
• The direction of these pins are all output not
  input
• Activate the segments required to make a 0
  appear
• Wait for one second
• Create the number 1

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Now modify the program so that the letters
A,b,C,d,E,F are displayed instead of the 0 - 9

• Note Pay attention to the difference in capital
  and lower case letters above..

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Using LOOKUP for Lists

• The LOOKUP command allows you to, well, lookup
  elements in a list.
• LOOKUP index,7,85,19,167,28,value
• Index is a variable to point to a list position
  with the 1st being the zero position.
• The values in 's are the list elements.
• Value is a variable that will be used to store
  the value that was indexed.

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• For example, if the value of index 0
• LOOKUP index, 7,85,19,167,28,value

If the value of index 3 LOOKUP
index,7,85,19,167,28,value
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Enter, Run, and Save the code below

• The LOOKUP command can be used to make displaying
  the 7-segment digits much cleaner and simpler.
  Note the data that index points to is loaded into
  OUTH!!

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Note the following

• The program functions the same as
  DisplayDigits.bs2
• The debug terminal shows how the value of index
  is used by the lookup command to load the correct
  binary value into OUTH list

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Using LOOKDOWN to Find Index

• LOOKDOWN works just opposite of LOOKUP in that
  where a value lies in a list returns the index
  for that value.
• LOOKDOWN value, 7,19,28,85,167, index
• For example, if value 19, 1 would be the value
  stored at the ones location. Since 19 is in the
  1-spot in the list, 1 will be stored in index.

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Enter, Run and save the code on the next slide
(Page 183)

• Run the program as is with value 167
• Observe the debug terminal to see the index value
• Try setting the value variable equal to other
  numbers in the lookdown list. Predict the debug
  terminal outcome, and check your answer

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You can also check to see if a value is gt,lt, or
to certain values

• Example
• value 35
• LOOKDOWN value, lt 7,19,28,85,167, index
• CHANGE LOOKDOWN AND VALUE TO THE LINES ABOVE, AND
  CHECK THE RESULT
• This would report the position of the number that
  35 is just less than or equal to. So in this case
  the answer would be 3

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Activity 4 Display Dial Position

• In this activity the segments of the display are
  lit to indicate the position of a potentiometer
  dial.

Build the circuit to the right.
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Lets use this to make the 7-segment display
mirror the position of the potentiometer

• Enter, Run, and Save the code on the next slide
  (page 184 of your text).
• Twist the potentiometer to see that the program
  works
• Adjust the code so the display more accurately
  shows the position of the potentiometer

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How DialDisplay.bs2 works

• Charge and discharge rc-circuitsave discharge
  time as time
• Find the approximate position of the discharge
  time in the list.save this position as index
• Load the segment settings saved at this index
  value into OUTH

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Your Turnadding a segment

• Save the current program as dialdisplayyourturn.bs
  2
• Modify the program so that it causes all six
  segments to light up as the pot is turnedas
  opposed to only five