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Project 4.1.1 Introduction to Sensors and Motors: Copier Jam Detector (DLB-VEX)IntroductionUp until this point in the course, almost all of your designs have utilized push buttons or switches as inputs and LEDs or seven-segment displays as outputs. In this design project, you will have the opportunity to incorporate motors and input sensors other than the ones you are familiar with on the Digital Logic Board (DLB). You will design, simulate, and create a Copier Jam Detector.

Equipment Circuit Design Software (CDS) Digital Logic Board (DLB) SN754410 Quadruple Half-H Driver or L298 H-Bridge Driver Resistors: (3) 100kΩ: (1) 180Ω: (1) 330Ω VEX DE Kit

o (3) Limit switcheso (1) 2-wire motor 393o Structural

Variable power supply or (4) AA Batteries with holder #22 Gauge solid wire

© 2014 Project Lead The Way, Inc. Digital Electronics Project 4.1.1 Copier Jam Detector (DLB) –

Procedure DesignDesign a combinational logic circuit that will monitor the copier’s three input sensors and activate both an LED and stop the feed motor whenever a paper jam is detected. The inputs from the three sensors (A, B, and C) and the output to the motor should be connected to four of the DLB’s general purpose I/O input pins. The clear signal should be connected to any of the DLB’s four pushbutton switches. The jam signal should be connected to any one of the DLB’s eight LEDs.

Your design will require a few additional features that will allow VEX sensors and motors (which were designed for different voltage levels) to be controlled by the PLD.

InputsAs a piece of paper passes through a copy machine, three sensors monitor its path. The sensors consist of a normally open SPST. In our design using VEX limit switches, we will only need to wire the signal wire (white) and the ground wire (black).

Note: If you were to open up the VEX limit switch, you would actually find that the red-wire is not utilized at all. It is not wired to anything.

When a paper closes the switch, the output is a logic one (1). When the switch is not closed (i.e., there is no paper), the output is a logic zero (0). 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.


OutputsWhen a paper jam occurs, an LED indicator light will turn on and a buzzer will sound (the buzzer is optional in your design). The feed motor should stop. The JAM indicator will go off as soon as the jam is cleared. The LED should remain lit until a reset button is pressed. This last condition requires that the output controlling LED output be latched with a flip-flop.

Voltage DividerVEX Limit Switches are designed for 3.3V. However (as you know) the DLB rails provide 5V. If you try to detect the jam with the VEX limit switches using 5V, you will not get a reliable signal. Some Digital Boards have a 3.3V power supply option. The following steps assume you do not have a 3.3V power supply option on the Digital Logic Board.

If you only have a 5V power supply option, we will need to lower the 5V closer to the 3.3V operating range that the VEX limit switch was designed for. One way to do this 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.)

V out= R 2

R 1+R 2⋅V in V out=330Ω

180Ω+330Ω⋅5V=3.24V

Pull Down ResistorsAnother 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.


Full Block Diagram

Powering Motors Separate from Your Logic DesignMotors 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. This protects your circuit design from inadvertently being powered by more than 5V and damaging the circuit. Also, as a motor acts as a load in the circuit, it can vary the voltage level and disrupt your logic design if the two were to be powered by the same source.

The SN754410 Quadruple Half-H Driver is designed to accept standard TTL logic levels and drive DC motors using separate power sources. The L298 Full Bridge Driver is another option for driving motors. An advantage of the SN754410 is that its DIP design makes it easier to breadboard.


Wiring Diagram: SN754410

Connecting the PLD to Inputs and Outputs

Figure (A)Wiring for Limit Switches and Motor


Figure (B) Figure (C)

SN754410 Quadruple Half-H Driver Voltage Divider and Pull-Down Resistors

Design Specifications The three inputs (VEX Limit Switches) will require 100K pull down resistors.

The three inputs (VEX Limit Switches) will require a voltage divider to change the signal voltage from 5V to 3.3V. (180Ω and 330Ω are recommended.)

The LED output and Motor output should remain on until the Clear pushbutton is pressed. This will require the push button to be latched with a flip-flop.

The Motor will require a SN754410 Quadruple Half-H Driver or L298 Full Bridge Driver.

The Motor MUST be powered by an external power supply providing 6V(Batteries or variable power supply).

Simulation (Design Mode or PLD Mode)Using the Circuit Design Software (CDS) enter and test your Copier Jam Detector.

Design Mode Option: If you choose to create the circuit in Design Mode to simulate it, remember that you will need to re-create the circuit in PLD Mode to prototype the circuit.

PLD Mode Option: You can bypass the need to re-create the circuit a second time by creating and simulating the circuit in PLD Mode. Just remember that you will not have an SSD for simulation in PLD Mode. You will need to use probes to track the counts and events.

Verify that the circuit is working as designed. If not, review your design work and circuit implementation to identify your mistake. Make any necessary corrections and retest. Be sure to document all changes in your engineering notebook.

PrototypingExport your Copier Jam Detector design to the Digital Logic Board (DLB). Make sure that the voltage divider, pull down resistors, and external power source with the H bridge are wired


correctly. Voltages over 5V can damage the DLB or components if they are not designed for 5V.

Verify that the circuit is working as designed. If your circuit isn’t working correctly, review your circuit implementation to identify your mistakes, make the necessary corrections, and retest. Be sure to document all changes in your engineering notebook.

ConclusionTechnical Report:

Your technical report will be written in MS Word and should include the following:

Introduction/Purpose of Project

Explanation of Operation

Explanation of Build

Explanation of Testing

Conclusion

Appendix

final Multisim and PLD schematics

parts list

image of your final project

image of testing

Technical Report Rubric

Non-existe

nt

F Level Poor

D Level Fair C Level B Level

GoodA Level

Excellent

Title Page 0 1 2 3 4 5Introduction/Purpose of Project 0 6 7 8 9 10

Description of Operation 0 6 7 8 9 20

Explanation of Build 0 10 13 15 18 20Explanation of Testing 0 7 9 11 13 15

Conclusion 0 6 7 8 9 10Appendix 0 10 13 15 18 20

Total Points Earned: ________ / 100


**Note: Explanations and descriptions should demonstrate intelligence of coursework,

engineering vocabulary (where applicable), and include comments on design strengths and weaknesses and possible design improvements.


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