Transcript Introduction to Sensors and Motors: Copier Jam Detector

Introduction to Sensors and
Motors: Copier Jam Detector
DMS-VEX or DLB-VEX
Digital Electronics
© 2014 Project Lead The Way, Inc.
Design Specifications
As the paper passes
through a copy
machine, three
sensors monitor its
path. The sensors are
switches that are
internally wired as
Normally Open.
Motor
Sensor
C
Sensor
B
Sensor
A
Paper Path
Test fixture constructed with VEX® components.
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Design Specifications
When paper makes contact with
the switch, the switch outputs a
logic one (1). When paper is not
present, the switch outputs a logic
zero (0).
Switch
If a jam occurs, the
feed motor will stop.
Paper
Paper = Logic 1
No Paper = Logic 0
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Design Specifications
Under normal operations,
paper will pass through
the sensors such that
adjacent sensors will not
simultaneously detect
paper. If they detect
paper, this indicates that
a paper jam has occurred.
No Jam
Jam
Jam
Shown are a few
examples of both Jam
and No Jam conditions.
No Jam
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Design Specifications
When a paper jam occurs, an
LED indicator light will turn on
(and/or a buzzer will sound).
Motor Signal
JAM Signal
The LED indicator will go off as
soon as the jam is cleared.
CLEAR Signal
The buzzer should continue to sound until a Clear button
is pressed. This last condition requires that the output
controlling the buzzer be latched with a flip-flop.
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Design Challenges: CMOS vs TTL
The Cmod-S6 PLD, the Digital Logic Board (FPGA), and
VEX limit switches are all designed for CMOS not TTL.
This means that the inputs to both these FPGA’s should
be kept ideally near 3.3V rather than 5V to protect the
hardware and for them to work with VEX limit switches.
Note: some pins on the DLB are not 5V tolerant and require that the voltage be
lowered to 3.3V or it will damage the board. Older DLB’s may have a 3.3V
option.
The new Digital Protoboard also has a 3.3 V option when using Vext.
-Pictured above
Regardless what development board you are using we will assume that the
power rail are providing 5V so that we may learn about voltage dividers.
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Design Strategy:
Voltage Dividers
One way to reduce the 5V provided to the 3.3V desired is to
use a voltage divider. A voltage divider is a linear circuit that
produces an output voltage which is a fraction of the input
voltage. (See schematic below.)
R1
R2
Vout 
R2  Vin
R1  R2
Vout 
330
 5 V  3.235V
180  330
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Design Strategy:
Pull Down Resistors
Another way to help distinguish between a high or low signal
at the inputs is to use pull down resistors.
Pull down resistors hold the logic signal near zero when no
other active device is connected.
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Design Strategy:
Switches
The red wire on the switch is not connect inside. The switch
is wired as a SPDT using only the black and white wires.
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Design Challenges: Motors
• Motors and other devices often
require more than the 5V used in
TTL logic to power them.
• In this case, the VEX 2-Wire
Motor 393 requires 6V to operate.
• It is often wise to ensure that the
power being supplied to the PLD
(or other controller) is NOT the
same power supply being used to
drive the motor.
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Design Strategy:
H-Bridge Drivers
Aside from keeping the motor voltage source separate from
the logic voltage source, in future designs we will want
motors to move in both directions.
An H bridge is an electronic circuit that enables a voltage to
be applied across a load in either direction.
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Wiring the SN754410
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Complete Block Diagram
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Challenge: Copier Jam Detector
Design Specifications:
• The copier jams only when 2 adjacent inputs are triggered.
• The MOTOR output should remain on until the copier jams.
• The LED should remain on and the MOTOR off until the
CLEAR pushbutton is pressed. This will require the
pushbutton be latched with a flip-flop.
• The design should include pull down resistors.
• The design should include a voltage divider to change the
signal voltage from 5V to 3.3V.
• The design should include a SN754410 Quadruple Half-H
Driver or L298 Full Bridge Driver and a 6V external voltage
source to drive the motor.
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Challenge: Copier Jam Detector
Challenge:
• DMS-VEX
• myDAQ supplying 5V to
the Digital Protoboard
• SN754410 Quadruple
Half-H Driver
• (4) AA batteries supplying
6V to the Motor
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