Transcript Microprocessor Motor Control

Microprocessor Motor Control
Spring 2004
Introduction
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Stamp projects
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Robots
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Rocketry
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Sensors
Motor control
Logic
Reading acceleration (“g” forces)
Logging & graphing data
Weather observations
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Weather station
Pond and house temperature
Objectives for Train Controller
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The train will be able to accelerate and decelerate
smoothly, run at a constant speed, stop and
sense its location on the track
All motor control will be solid state
The model train will operate from batteries
Objectives for Train Controller
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A microprocessor will control the train’s motion
The microprocessor will must use interrupts to
detect crossing over a magnet so that no magnet
crossings are missed
Motor speed control will be by PWM
It will be possible to change some settings
without reprogramming
Programs will be easy to create and revise
Hardware – Microprocessor
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The microprocessor is a PICAXE 18X
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This 18 pin device is programmed in a
simplified version of the BASIC language
It has 8 pins that can be used as
outputs and 5 pins for inputs.
In this project the input pins will be
used to detect switch closures and the
position of two potentiometers
The output pins will operate the motor
and give us some feedback with LEDs
It can use interrupts to sense magnets
It can control motor speed with PWM
Hardware – H-Bridge
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Motor control is accomplished with
an LM293D H-Bridge chip
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This 16 pin device can control the
speed and direction of two DC
motors, each drawing up to 600
ma.
In order to increase the amperage
available to the motor the two
independent circuits on the LM293D
chip will be wired in parallel. This
will provide more than 1 amp of
power to the motor.
Three pins on the LM293 will be
connected to the PICAXE. Two are
used for direction control and the
third for PWM speed control
Hardware – Sensors
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Reed switch sensors
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In order for the microprocessor to know where the train is
located on the track a reed switch is located under the
train. Magnets are placed on the track to signal when an
event should take place (speed up, slow down or stop)
Reed switches are small glass tubes containing two small
magnetized metal contacts, or reeds. They normally don’t
touch. When a magnet comes close to the reeds they
come together, completing the circuit until the magnet
moves away.
Reed switches are commonly used in burglar alarm systems
(reed switch in a window frame and a magnet in the
window – when the window opens the magnet moves away
activating the alarm)
They are very reliable. They are commonly used as the
speed sensor on a bicycle speedometer where they sense
each rotation of the wheel. In this application they can
open and close more than 700 times for each mile that the
bicycle travels.
Hardware - Other parts
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LEDs are small lights that can be run directly
from the output pins on the PICAXE. All that
is needed is a 470 ohm resistor in series
with the output pin to limit the amount of
current that the LED draws.
Potentiometers are variable resistors having
three connections, one at each end of a fixed
resistor and a third that is a wiper that
moves across the fixed resistor giving
variable resistance readings. In this
application two will be used to set the
motor’s maximum speed and the amount of
time that the motor will be off when it
pauses between direction changes.
Hardware - Other parts
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A 78L05 voltage regulator is
used to supply a steady 5 volt
power supply to the PICAXE.
Connecting the microprocessor
directly to the 14.4 volt power
supply would instantly destroy
it.
Capacitors are used in the
power supply circuit to filter out
electrical noise that may be
introduced into the circuit by
sparking in the motor. Without
these devices the
microprocessors can reset
randomly and give unreliable
operation.
Prototype – Schematic
Prototype – Hand Wired Board
PC Board design and creation
PC Board
 Software
free on-line at
www.expresspcb.com
 All communication done with the
program
 Three day service
 Revision
Fine tune component placement
 Correct errors
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Building and testing
 Time
to construct went from 3 hours
+ to 20 minutes
 Errors almost eliminated
Solder bridges
 Incorrect component placement
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Software to test LED & Switch
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Load the “testLED.bas” program into the
computer. It simply flashes the two
LEDs until you put a magnet next to the
reed switch. When the reed switch is
activated the LEDs stay on for 5 seconds
then start flashing again.
start:
high 7:low 6
if pin6 =1 then reed:
pause 300
low 7:high 6
if pin6 =1 then reed:
pause 300
goto start:
reed:
high 6
high 7
pause 5000
goto start:
Software to test Motor
Load the “testMOTOR.bas”
program and download it to
the PICAXE
 The motor should slowly
accelerate, pause for 5
seconds, decelerate, stop,
pause and repeat.
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high 1
low 2
start:
for w1= 200 to 1000
step 40
pwmout 3, 249, w1
pause 400
next w1
pause 5000
for w1= 1000 to 200
step -40
pwmout 3, 249, w1
pause 400
next w1
pause 5000
toggle 1
toggle 2
goto start:
Software to test Speed & Pause Time
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The last test determines if the potentiometers
are working. This test uses a built in function
of the programming language that
automatically sends information to the
computer screen. It is called “debug”
Load the “testpot.bas”program and download
it to the PICAXE
In a few moments a “debug window”should
appear on the computer’s screen.
Make sure “Byte”is selected at the bottom of
the debug screen, not “Word”
Watch the value of B0 and B1 – as you turn
the potentiometers one way or the other these
values should vary from 0 to 255.
start:
readadc 1, b0
readadc 2, b1
debug b0, b1
goto start:
Other projects
 Pond
temperature
 House temperature
Thank You!
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Questions?
Model Rocket Acceleration
Pond Temperature
House Temperature