Computer Engineering Project report

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Boe-Bot Activity

The Boe-Bot robot

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Image source: Robotics with the Boe-Bot —Student Guide

Boe-Bot Circuit Board – Rev D

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Moving the Boe-Bot

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 The Boe-Bot is equipped with servo motors and a microcontroller (“brain” ), which can be programmed by the user

 The Boe-Bot’s wheel movement is controlled by the rotation of these servo motors

 The servo motors’ rotation are, in turn, controlled by electrical pulses applied to specific circuit pins of the Boe-Bot’s “brain”

 Each such pin has a number

 Pulses of varying widths can be sent to the pins by the user (you!) via a program Controlled rotation of servo motors  Controlled movement of the Boe-Bot!

Pulses

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 Each HIGH pulse rotates the servo motor

 The direction of rotation is determined by the width (duration)

of the HIGH pulse

 Successive HIGH pulses are separated from each other by a

PAUSE

Pulses – cont’d

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 A HIGH pulse lasting for 1.3 ms (milliseconds) rotates the servo motor clockwise

 A HIGH pulse lasting for 1.7 ms rotates the servo motor counter-clockwise

 A HIGH pulse lasting for 1.5 ms causes the servo motor to stay still

How to apply pulses to pins via

programming?

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 Use the PULSOUT command of the PBASIC programming language

 The PULSOUT command’s argument generates a pulse (at pin N) that lasts for Argument * 0. 002 milliseconds i.e.

Actual duration of pulse = Argument * 0. 002 milliseconds

 Rearranging the equation,

PULSOUT Argument = Actual Duration in milliseconds * 500

 Example: The command,

PULSOUT 12, 650

generates a HIGH pulse lasting 1.3 ms at pin 12, causing the servo motor connected to pin 12 to rotate full-speed clockwise

Example Code: Moving Boe-Bot for 3 seconds

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' {$STAMP BS2}

' {$PBASIC 2.5}

DEBUG "Boe-bot is running the program“

counter VAR Byte

FOR counter = 1 TO 122 'Runs the FOR loop 122 times; initially, counter = 1

PULSOUT 13, 850 'Generates 1.7 ms pulse at pin 13 (pin 13 servo rotates counterclockwise)

PULSOUT 12, 650 ' Generates 1.3 ms pulse at pin 12 (pin 12 servo rotates clockwise)

PAUSE 20 'Pause for 20 ms between pulses

NEXT 'Increment counter by one and repeat loop (repeat till counter = 122)

'Time overhead due to the number of instructions in the loop = 1.6 ms

'TIME TAKEN FOR ONE LOOP EXECTION = 1.7 + 1.3 + 20 + 1.6 = 24.6 ms

'TOTAL TIME OF BOE-BOT MOVEMENT= 122 * 24.6 ms = 3 seconds (approx.)

END

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Exercises

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 Read slides 4 through 8

 In the program handouts given, replace the question mark

symbols (??) with actual numbers to achieve desired Boe-Bot

movement

 Test your answers on Boe-Bot

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Exercise 1: Moving Boe-Bot backwards for 5 seconds

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' {$STAMP BS2}

' {$PBASIC 2.5}

DEBUG "Boe-bot is running the program“

counter VAR Byte

FOR counter = 1 TO ??

PULSOUT 13, ??

PULSOUT 12, ??

PAUSE 20 'Pause for 20 ms between pulses

NEXT 'Increment counter by one and repeat

'Time overhead due to the number of instructions in the loop = 1.6 ms

'TIME TAKEN FOR ONE LOOP EXECTION = 1.7 + 1.3 + 20 + 1.6 = 24.6 ms

END

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Exercise 2: Keeping the Boe-Bot still for 3 seconds

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' {$STAMP BS2}

' {$PBASIC 2.5}

DEBUG "Boe-bot is running the program“

counter VAR Byte

FOR counter = 1 TO 122

PULSOUT 13, ??

PULSOUT 12, ??

PAUSE 20 'Pause for 20 ms between pulses

NEXT 'Increment counter by one and repeat

'Time overhead due to the number of instructions in the loop = 1.6 ms

END

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Exercise 3: Identify the wheel controlled by pin 12

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' {$STAMP BS2}

' {$PBASIC 2.5}

DEBUG "Boe-bot is running the program“

counter VAR Byte

FOR counter = 1 TO 122

PULSOUT 13, ??

PULSOUT 12, ??

PAUSE 20 'Pause for 20 ms between pulses

NEXT 'Increment counter by one and repeat

'Time overhead due to the number of instructions in the loop = 1.6 ms

END

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Questions??

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Thank you!!

P.S. Nair