Transcript Day 2

PHY 235 Robotics Workshop
Day 2
ZX-24a Microcontroller,
Servo Review, and I/O
Workaround to “Unplug” problem
• Many have been having problems with the
ZBasic IDE not working when you unplug and
re-plug the usb cable.
• The problem comes from undoing the usb
connection – this confuses the usb controller.
• The solution is to only unplug the serial
connector.
ZX-24a
• The ZX-24a circuit board includes a microcontroller, the Atmel ATmega644P.
• Additional components on this small board
provide micro-controller support.
ZX-24a
5V Regulator 78L05
Regulates voltage
to 5V with a supply of
5.5VDC to 15VDC
Interpreter Chip
ATmega644P
Reads the ZBASIC
program from the
EEPROM and executes
the instructions.
Green/Red LEDS
EEPROM
AT25256A
Stores the tokenized
ZBASIC program.
Crystal 14.7456MHz
Sets the speed at which
instructions are processed.
ZX-24a
• The ZX-24a is programmed in ZBasic, a version
of the BASIC programming language.
• Code is written in the ZBasic IDE and
downloaded to the chip on the Boe-bot Board
of Education (BOE) circuit board.
How is a Program Run?
• A program is written
in the Zbasic IDE.
• The program is tokenized,
or converted into symbolic
format.
• The tokenized program is
Tokenizer
transmitted through the USB
cable and stored in EEPROM memory.
• The ZX-24a microcontroller reads the
program from EEPROM and
executes the instructions.
How is a Program Run?
• NOTE: Once you choose “Go” from
the Project menu, the program is
immediately downloaded to the
ZX-24a and run on the chip.
• Even if you unplug the USB cable, the
program will continue running on the chip.
• Each time you hit the reset button on the
board, the program will restart on the ZX-24a.
Servo Motors
• A servo is a single device that contains:
– Motor
– Gearbox that gears down the motor to provide
slower speeds (than most motors) and higher
torque (power to turn).
– Built-in electronics such that the motor position
or speed can be controlled by a series of pulses.
The servo is powered using 5V (4.8 – 6.0 V)
Servo Motors
Servo Motors
• Servo Speed is controlled by varying the pulse
width of a control signal.
Full speed CW
Stop
Full speed CCW
CW
Stop
CCW
Controlling Timing and Pulses
• Call Delay(duration)
– Duration is in seconds
Example: Call Delay(2.0) is used to have the
microcontroller wait for 2.0 seconds.
• Call Pulseout(pin, duration, level) is used to
generate a pulse on pin number pin of duration
duration (seconds). Level indicates the transition
state of the pulse.
– Example: Call Pulseout(17, 0.0013, 1) generates a
pulse of duration 1.3 ms on pin 17, going from 01-0
Timing and Pulses Example
For i = 1 to 100
call pulseout(17, 0.0013, 1)
call delay(2.0)
LOOP
Sends a 0.0013 second (1.3ms) pulse to IO pin p12
(actual physical pin number 17) every 2.0 seconds
0.0013
0.0013
Pulses for Servos
The pulse width defines the direction and speed
of the servo motor.
– 1ms = Maximum speed one direction
– 1.5ms = Stopped (Halfway between max-min)
– 2ms = Maximum speed other direction
• Note: When running the servos, if you have
problems, consult the trouble-shooting guide
on page 104 of Robotics with the Boe-Bot .
Boe-Bot Servo Example
const p12 as byte = 17
const p13 as byte = 18
const fwd as single = 0.002
const rev as single = 0.001
Dim i as Integer
Sub Main()
for i = 1 To 5
call forward(1.0)
call delay(1.0)
next
End Sub
'pin 12 reference
'pin 13 reference
'pulse width for servo motor on p12
'pulse width for servo motor on p13
'define a variable i
sub forward(byval turntime as single) 'drive forward
dim starttime as single
starttime = timer()
do while (timer()-starttime)<turntime
call pulseout(p12,fwd,1)
call pulseout(p13,rev,1)
call delay(0.02)
loop
end sub
Timer Code
• Timer() returns the current RTC (run-time clock)
time represented as the number of seconds since
midnight with a best-case resolution of 1.95ms.
• sub forward(byval turntime as single)
is a subroutine that has the servos rotate for
turntime seconds. (in opposite directions- why?).
• The use of timers will be critical in our Robopong
contest, as each robot will be expected to run for
exactly 60 seconds.
Boe-bot Programming
• The biggest task for controlling our robot
will be to effectively design and test
programs.
• Design: Sensors, timing, motors
• Test: Running program, Modifying code if
needed, Re-test.
Example: Beep-Beep
• Task: Have Boe-bot produce a Beep-Beep sound (like
the roadrunner)
• We will use an external output device, a piezoelectric buzzer. This buzzer can make different tones
depending on the frequency of high/low signals it
receives from our microcontroller. The schematic
symbol and part drawing for the piezoelectric buzzer
are shown here:
Beep-Beep Circuit
• We will send out a Hi-Lo
frequency pulse on pin P4. We will
attach the buzzer’s positive (+)
terminal to pin p4 and the other
terminal to ground (Vss), as shown:
FreqOut
• FreqOut(pin, freqA, freqB, duration)
• From the help page: “This routine generates a signal
on the specified pin that is a digital approximation of
two superimposed sine waves having the specified
frequencies.”
• Example:
Call FreqOut(pin, 440, 880, 5.0) ' play middle C/high C 5 sec
Beep-Beep Program
const tone as Integer = 10000
const p4 as byte = 9
dim i as integer
' 10 khz tone
' ouput tone on p4 pin
Sub Main()
' send message to debug window in ZBasic IDE
debug.print "Watch out Wile E!"
for i = 1 to 2
' send tone for 0.1 second
call freqout(p4, tone, tone, 0.1)
' wait 0.1 second
call delay(0.1)
next
End Sub
Beep-Beep Program
• Download and run this program. (It is called
“beepDay2” on the Code page of our course web
site)
• Note the use of the code debug.print "Watch out Wile E!"
This serves as a “print” statement to the output area
in the ZBasic IDE. The ability to print out messages,
and the state of variables, will be useful for testing
and debugging our code.
Whiskers I/O
• The Beep-Beep program is an example where we
send output over an I/O pin connection. In our next
example we will look at how to use an I/O pin to
gather input.
• Do Activity #1: BUILDING AND TESTING THE
WHISKERS on pages 165-171 in the Boe-Bot text.
• Then, use the program on the next slide to test the
whiskers. Note how we use the debug.print
command to display the state of the whiskers. (It is
called “beepDay2” on the Code page of our course
web site)
Whiskers Program
const p5 as byte = 10
const p7 as byte = 12
dim p5value as byte
dim p7value as byte
Sub Main()
do
p5value = getpin(p5)
p7value = getpin(p7)
debug.print "p5 = "; p5value;" , p7= ";Cstr(p7Value)
loop
End Sub
Whiskers I/O
• Test the whiskers by
pressing them so that
they make contact with
the 3-pin black “headers”
• You should see a
transition from 1->0 in the
output of the program as
the whiskers touch the headers.
Whiskers Program Code
• GetPin(pin)
If the specified pin is configured to be an input, this function reads
the state of the pin and returns the value 0 or 1.
If the pin was configured to be an output, it is reconfigured to be
an input before reading the input value.
• Debug.Print stringList
This method is used for outputting debugging information. The
argument stringList consists of zero or more strings or values
each separated by a semicolon. If non-string values are
supplied, they are converted to strings using the CStr()
function. Unless the list ends with a semicolon, a carriage
return/new line will also be output after all of the strings have
been output
Whiskers Circuit
• To understand how the whiskers program works, we
need to understand a bit about electronic circuits.
• Here is the whiskers circuit:
We can think of the two
whiskers as switches. The
other components in the
circuit are resistors and
connecting wires.
Circuits
• Electrical circuits involve the flow of electrons
through devices. We analyze this flow using the
following measurements:
V = Voltage
R = Resistance
I = Current
• The info in the next few slides was created by Parallax (the
maker of our robots) and adapted by Martin Hebel at
Southern Illinois University for use in a robotics camp he runs
each summer.
Voltage, Current, Resistance
Voltage and current can be compared to water pressure
and flow. Resistance is like a valve that can be
opened and closed (Or like the size of the pipe).
When the valve is opened (or the pipe is widened),
flow increases, but pressure decreases.
Voltage, Current, Resistance
Of course water will flow from the fuller tank because it
has greater pressure than the empty tank.
The flow rate is dependent on:
• The difference in pressure between the two tanks.
• The amount of restriction to flow in the pipe and
valve.
The water that flows from your faucet is dependent on
the height of your town's water tank, the size of the
pipes, and how far you open the faucet.
Voltage, Current, Resistance
In a battery, there is surplus of electrons on one side,
and a deficiency of electrons on the other side
(holes).
When a circuit is completed, such as putting an LED in
it, a flow exists from one side to the other. This is
called the Current.
Voltage, Current, Resistance
• The greater the pressure, (the difference in
electrical potential), or voltage, (measured in
Volts), the greater the amount of current that
can flow in a unit time (measured in
Amperes).
• The greater the restriction to flow (resistance
– measured in Ohms), the lower the amount
of current that can flow.
Ohm’s Law
• Ohms Law states: The amount of current (I)
that will flow is proportional to the voltage
applied (V), and inversely proportional to the
resistance (R) of the circuit.
I = V/R
( V = IR)
• As Resistance increases, current decreases.
The Resistor
The resistor is a device used to limit the amount of
current in a circuit. Because it is so small, color
bands are used to identify the value.
Schematic
Symbol
•
Band: Digit
• 2nd Band: 2nd Digit
• 3rd Band: Multiplier (number of zeros to add)
• 4th Band (if present): Tolerance. (Gold or Silver)
1st
1st
Part
Drawing
The Resistor
For the resistor shown:
Yellow = 4, 1st Digit
Violet = 7, 2nd Digit
Brown = 1, add 1 zero.
470 Ohm or 470
Tolerance is how far off it
could be from the labeled
value:
Gold: 5%
Silver: 10%
none: 20%
Whiskers Circuit
• Now that we know a bit about circuits, let’s look at
the whiskers circuit again. This circuit makes use of 2
10K Ohm resistors. These are used as Pull-up
resistors.
• (material on the next few slides is from
http://www.seattlerobotics.org/encoder/mar97/basics.html)
Pull-up Resistors
• In this figure consider the triangle to be our
microcontroller with a connection from IO pin 1
ZX-24a
to a switch, which is connected to ground (0 volts).
• When switch S1 is closed (on), the input state
at pin1 goes low (0 volts). Since there is a definite
connection to an electrical potential (in this case ground),
the Input state of the pin is 0 and this value is stable.
• When switch S1 is open (off), then pin1 is susceptible to
electrical problems. Other wires connected to pin 1 may allow
electrical noise in (by acting as little antennas), causing pin 1 to
incorrectly switch from 0 to 5 volts or vice-versa. The input
voltage can then float to any value. This is BAD!!
Pull-up Resistors
• What is needed is a way to connect pin 1 to an
electrical potential to allow the pin to keep a
steady state, whether the switch is open or closed.
• Our first attempt at a solution is to connect
pin 1 to Vcc (+5 volts) to insure that pin 1 doesn't
float when the switch is open. However, we now
have a problem – when the switch is closed we
have a direct connection from Vcc to ground – a
SHORT CIRCUIT. Since R=0 from Vcc to Ground , we would
create an enormous current that can fry our components!
Pull-up Resistors
• The solution to this dilemma is to add a resistor
between Vcc and pin 1 to limit current when the
switch is closed.
• Now, when switch S1 is open (off), pin 1 is tied to
Vcc through the resistor. Since pin1 is a high resistance
input, a voltage meter or logic probe placed on pin 1
will show Vcc (+5v) if connected to pin 1. (Since a
small amount of current will go through R1, the voltage will still
be about 5 volts at pin 1.)
Pull-up Resistors
• When switch S1 is closed (on), pin 1 has a direct
connection to GND, which takes it to the low state.
The pin1 side of R1 also has a direct connection to
ground. Current will flow from Vcc, through R1, and
to ground. It isn't considered a short, however,
because R1 will limit the amount of current that can
flow to a very small amount. In fact, you can compute
this using Ohms law.
Thus, opening and closing
the switch will yield a value
I=V/R
of 5 volts or 0 volts at pin 1.
I = 5v / 10,000ohms
We can interpret this as 1-0
or True-False
I = .0005A (.5mA)
Pull-up Resistors
• Pull-up resistors are extremely common in
digital circuits. Their function is to keep input
lines from floating erratically from one state to
another.
• The key function for the resistor is to prevent
too much current from flowing through the
pull-up circuit.
Whiskers Circuit
• The two 10K Ohm resistors are used as Pull-up
resistors. The 220 Ohm resistors serve as an
additional protection to limit current into the input
pins.
Team Tasks
• Modify the Whiskers program so that the Boe-bot
emits a “Beep-beep” when one or both whiskers are
pushed.
• Modify the Whiskers program so that it uses the
servos and the whiskers to create a navigation
program. That is, add the capability to have the Boebot move forward and when it hits something
(whiskers are pushed) it backs up, turns a different
direction, and continues forward.
Team Tasks
• For the second program, you will probably need to
use conditionals.
if (p7value = 0 and p5value =0) then
(back up and turn) ‘whiskers closed
elseif (p5value = 1 and p7value = 1) then
(go forward) ‘whiskers open
else ??
endif
Team Tasks
• For some ideas on doing this task, you can look at
Activity #3: NAVIGATION WITH WHISKERS in
Chapter 5. The code in that section is not ZBasic, but
you should be able to translate the ideas into ZBasic.
• Suggestion: To make your coding more adaptable,
model your forward, reverse, and turn sub-routines
after the forward example included earlier in these
slides.
• If you want a further challenge try the one on the
next couple of slides.
Wall Following
• Program the BOE-BOT to follow the outside (leftt)
wall. Do this by giving the BOE-BOT a slight bias
(drift) to the left.
• You will have to re-design the whisker system so that
a whisker makes contact with the 3-prong header
when it touches the wall.
• When the left whisker hits the wall, the robot should
turn right for a short time and then resume the slight
bias to the left.
• This is illustrated on the following slide.
Wall Following
Path of
robot
Place where left
whisker hits the
wall
Robot naturally
drives slightly to the
left and then corrects
right after left
whisker hits the wall
Right
Whisker
Adding angled
barriers to
corners may
make
navigation
easier
Areas of
difficulty?
(source: http://www.tcc.edu/faculty/webpages/PGordy/Egr120/