The Board of Education Breadboard,

PBASIC, and Servos

EGR1301

Connecting an LED

Electricity can only flow one way through an LED (or any diode).

LED = Light Emitting Diode

Diagram from the Parallax Robotics book

Building an LED Circuit

Vdd = 5V

LED

5V

+ -

470W

These circuit diagrams

are equivalent

these holes are “connected”

Vdd =

LED

holes in this direction are not connected

Diagram from the Parallax Robotics book

Replace the 470W Resistor

with the 10kW Resistor

What happens and Why??

ANSWER: The smaller resistor (470W) provides less resistance to current than

the larger resistor (10kW). Since more current passes through the smaller

resistor, more current also passes through the LED making it brighter.

What would happen if you forgot to put in a resistor?

You would probably burn up your LED.

www.radgraphics.net

Voltage regulator supplies Board of Education

with regulated 5 VDC (Vdd) and ground (Vss)

Servo power selector:

• Vdd regulated 5 VDC

•Vin connects directly to the Board of Education’s power source

Header for connecting power (Vdd, Vin,

Vss) to circuits on the breadboard

4 R/C servo connection ports

for robotic projects

Header for connecting BASIC Stamp I/O

Pins to circuits on the breadboard

Breadboard rows are connected

horizontally, separated by the trough

Application Module (AppMod) connector for add-on modules

Power indicator light

Power jack 2.1 mm center positive 6-9 VDC

Three-position switch

0=power OFF

1=power ON / servo ports OFF

2=power ON / servo ports ON

Filter capacitors for 5 VDC regulators on

Board of Education and BASIC stamp

Serial port connector for downloading

PBASIC programs and debug terminal

runtime communication

Socket for any 24-pin

BASIC stamp module

Reset button may be

pressed and released

to restart you BASIC

Stamp program

9 VDC battery clip

Diagram of the Board of Education

Based on Figure B-2 in the Parallax Robotics Book (Version 2.2)

BASIC Stamp Pinout

16 general purpose I/O pins

Serial communications

Power

Reset

A Pinout diagram shows what the

pins on a microcontroller are for.

Pins are numbered starting in the

top left, ending in the top right.

The same information is

printed on your Boe-Bot board.

http://www.dlwrr.com/electronics/tools/bsla/

The Editor

Any line that starts with an

apostrophe is called a “comment”

and is ignored by the processor.

These two commands are called

“directives” and identify the hardware

and software associated with the

program. Even though they look like

comments, the editor interprets your

code based on these directives (so

they are very necessary).

The DEBUG command displays text on the computer.

An END command is optional, but recommended as it

puts the Stamp into a low power mode.

Running a Program

Once the code

is written, turn

on you Boe-

Bot and press

“play” to

download it.

This box

will appear

briefly

during the

download.

Connect the Resistor to Pin 12 (P12)

' {$STAMP BS2} ' {$PBASIC 2.5} DO HIGH 12 PAUSE 500 LOW 12 PAUSE 500 LOOP

Enter and run the following PBASIC program:

Diagram from the Parallax Robotics book

Causes pin 12 to output a constant 5V (Vdd)

' {$STAMP BS2} ' {$PBASIC 2.5} DO HIGH 12 PAUSE 500 LOW 12 PAUSE 500 LOOP

How the Program Works

infinite loop

Causes pin 12 to output a constant 0V (Vss)

wait 500 ms

Wait 500 ms

Diagram from the

Parallax Robotics book

Experiment on your own!

(1)Try changing the time to 1.5 seconds on and 1 second off

(2)Connect the resistor to pin 8 and change the program to match

(3)Blink out SOS in Morse code (dot-dot-dot-dash-dash-dash-dot-dot-dot)

a. three short pulses (0.25 seconds each) followed by . . .

b. three long pulses (0.75 second each) followed by . . .

c. three short pulses (0.25 seconds each) followed by . . .

d. a brief pause (1 second)

e. repeat a through d using an infinite loop

' {$STAMP BS2} ' {$PBASIC 2.5} DO PULSOUT 12, 65000 PAUSE 2000 LOOP

Enter and run the following PBASIC program:

Another Way to Make the LED Blink

Causes pin 12 to output a constant 5V for . . .

65000 x 2ms = 130000 ms = 0.13 s Wait 2000 ms = 2 s

Diagram from the Parallax Robotics book

Find the PULSOUT Command Using PBASIC Help

Now, change the program to make the LED blink on for a duration of 0.01

seconds and off for a duration of 0.1 seconds.

Servos

Servo Operation

• Two types: – Continuous rotation

– Standard

• Speed and direction controlled with a pulse train – series of pulses

20 ms

Pulse width varies between

1.3-1.7 ms www.parallax.com

Duration Pulse Width (ms) Servo Action

650 1.3 Full speed CW

700 1.4 ~1/2 speed CW

750 1.5 Stopped

800 1.6 ~1/2 speed CCW

850 1.7 Full speed CCW

Pulse Width vs. Speed Table

Note 1: Speed is NOT linear with pulse duration.

Note 2: To move your Boe-Bot in one direction (either forward or

backward), the servos will have to rotate in opposite directions (i.e. one

CW, the other CCW).

Writing Code for the Servo

This code

moves the

Boe-Bot

forward while

the counter

variable rises

to 122.

The DEBUG

command

writes the

value of

counter on

the screen.

Variables

• Work like variables in algebra

• Hold a value

– Numbers

– Characters (i.e. individual letters)

– String (i.e. groups of letters)

• Can change the value (i.e. they can “vary”)

Name of variable,

could be anything

(e.g. “fido”) Keyword that specifies

we are creating a variable

Keyword that specifies

how much memory this

variable uses

FOR/NEXT Loops

• Executes commands a specific number of

times (or “iterations”)

• Uses “counter” as the variable which

tracks the number of iterations (hence the

programmer named it “counter”)

FOR Loop Timing

• How long do the servos run?

– Sum of times

– Times number of iterations

– Let’s time it!

– What’s wrong?

1.3 ms

1.7 ms

20 ms

+ 1.6 ms

24.6 ms

– Servo on P12

– Servo on P13

– Pause

– Code overhead

– Total

24.6 ms * 122 = 3001 ms = 3 s

Actual time = ~5 s

FOR Loop Timing Cont.

• What is “Code overhead”?

– Amount of time required for the processor to

execute the commands, which includes:

• incrementing the counter variable

• sending messages to the Debug Terminal

• other things

• Remove the DEBUG command

– Could also “comment out”

• Now lets time it! Actual time = ~3 s

PBASIC Commands Used

• DEBUG – prints to the Debug Terminal on the computer

• END – puts the BASIC Stamp in a low power state

• HIGH & LOW – sets a pin to either +5 V or 0 V

• PAUSE – temporarily suspends execution

• DO/LOOP – executes statements in an infinite loop

• PULSOUT – pulses a pin for a specific amount of time

• FOR/NEXT – executes statements for a specific number of

iterations

• VAR – creates a variable that can be used in the program

Programming Tips

• Use comments!

• Use variable names that mean something

(e.g. “counter”, “Lspeed”)

– But don’t use other keywords (e.g. HIGH, END)

• Use Help to learn syntax

End of Lecture…

BUT

Experiment with your Boe-Bot,

Make it go forward, backward, turn

corners, drive in a square, etc…