Download Activity 3.1.1 inputs and Outputs

Activity 3.1.1 Inputs and Outputs
Introduction
You might notice that sometimes your cell phone indicates that you are using a
digital signal and at other times an analog signal. Unless you have a crystal clear
connection, there is no need to look at your phone to determine whether it is
processing the information in a digital or analog format. If you hear static or the
signal seems to be fading, then you are using an analog signal. If the connection is
sharply cutting in and out, alternating silence and sound, it is a digital signal. Both
signal failures are annoying, but you should notice a distinct difference between the
two. The digital signal either exists or it doesn’t, while the analog signal can
gradually fade in and out.
Equipment
fischertechnik® components:
 Interface, power supply, and USB cable
 RoboPro
 4 complete wires
Inputs
Outputs

Mini switch

Lamp

NTC resistor

Motor

Potentiometer

Buzzer

Reed switch

Electromagnet

Phototransistor

Photoresistor
Procedure
In teams of two or three, you will experiment with different inputs and outputs. You
will learn how digital and analog inputs behave in addition to normally open and
normally closed inputs.
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POE – Unit 2 – Lesson 3.2 – Activity 3.1.1 – Inputs and Outputs– Page 1
1. Plug in and connect the power supply to the interface, then connect the USB
cable to the interface and computer.
2. Open RoboPro software and select COM/USB from the toolbar. In the
Interface/Port dialog box, select the USB radio button and ROBO Interface (New)
radio button. Select OK.
3. Select Test from the toolbar. The Connection box in the lower right corner of the
interface test dialog box will be green, indicating that the interface is running. If
the connection indicates simulation mode, check all connections and verify that
USB is selected under COM/USB. Leave the Test Interface box open.
Interface Connections
Refer to the image below in order to identify connection ports on the interface and
port monitoring locations on the Interface test window.
Digital Inputs
Digital systems consist of two states – on and off – and are typically represented as
one and zero. One indicates the presence of voltage, while zero indicates the
absence of voltage.
In fact all of the information on your computer is transferred through ones and zeros.
Alternating pulses of voltage are used to send information. A picture on a computer
screen is stored as ones and zeros. When you see that picture, it is a result of the
computer deciphering the ones and zeros to produce a particular image. A common
light switch is a simple way to think of a digital input. There are only two possibilities,
on or off. These two possibilities can be thought of as one or zero. If you designed a
code to talk to someone across the street by flipping a light on and off in certain
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POE – Unit 2 – Lesson 3.2 – Activity 3.1.1 – Inputs and Outputs– Page 2
patterns, you would fundamentally be communicating information the same way as
computers.
Interface digital inputs are I1 – I8. The conditions of I1 – I8 are observable in Test
Interface mode. When the boxes are unchecked, the condition is zero. When the
boxes are checked, the condition is one.
4. Connect the mini switch to the digital input labeled I1 on the interface. The switch
possesses three connection points. They are labeled 1, 2, and 3. The switch is
not polarity sensitive. Connect to pins 1 and 3 on the mini switch.
5. In the test interface window, what is the condition of I1 when you are NOT
pressing the switch?
Checked or unchecked? _____________
One or zero? _____________
Is voltage present or not present? _____________
6. In the test interface window, what is the condition of I1 when you are pressing the
switch?
Checked or unchecked? _____________
One or zero? _____________
Is voltage present or not present? _____________
7. Move the wire in connection 3 on the mini switch to connection 2. Repeat the
testing process in steps 5 and 6. What has changed about the behavior of the
switch?
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Normally Open and Normally Closed
The mini switch has the ability to be either normally open or normally closed. Using
connections 1 and 3, the switch was initially wired to be normally open. In other
words, the electrical circuit contains an open connection, resulting in no electricity
flowing through the circuit. When the switch is pressed, it closes the circuit path. This
allows electricity through the circuit.
When the wires were moved to connections 1 and 2, the circuit under normal
conditions was closed. Since the circuit was normally closed, pressing the mini
switch opened the circuit. This allows no electricity to pass through, resulting in a
signal of zero.
Analog Inputs
Analog signals are variable. The signal might appear anywhere in a range. While a
standard light switch sends a message for the bulb to be either on or off, a dimmer
switch can change the intensity of the bulb. A dimmer switch behaves as an analog
input. Radio volume can also be thought of as an analog input. You will use two
analog inputs on the interface. They measure resistance and are labeled AX and
AY.
8. Connect the potentiometer to the analog input AX on the interface. It is not
polarity-sensitive. Twist the potentiometer with your fingers and watch how the
numbers change in the Interface test window box AX.
9. Record the numeric value range of the potentiometer. _____ to _____
10. Connect the NTC Resistor to the AY analog input. It is not polarity sensitive.
11. Record the value of the NTC resistor. _____
12. Place the NTC resistor between your fingers to warm it for 10 seconds. Record
the new value. _____
Outputs
The interface has four power outputs. They are labeled M1 – M4. The Test Interface
window provides several options for controlling the output. You can change the
power sent to the outputs by sliding the scale between 1 and 8. You will also notice
that you have the option of clockwise (cw) or counterclockwise (ccw). Although the
shaft of a motor will change rotational direction when you toggle between cw and
ccw, all that is really happening is that the polarity is switching.
13. Connect a motor to M1 and a buzzer to M2. Experiment with the different
speeds and direction changes.
14. Describe how you can change the direction the motor shaft rotates without
switching between cw and ccw.
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15. Connect the reed switch to I1 and the electromagnet to M1. Set M1 to CW 8.
Position the reed switch approximately three inches away from the
electromagnet. Slowly move the reed switch closer to the electromagnet until
they are touching. Describe the relationship between the reed switch and the
electromagnet.
16. Does the reed switch behave as normally closed or normally open?
17. Connect the lamp to an output, the phototransistor to a digital input, and the
photoresistor to an analog input.
18. Describe the relationship between the photoresistor and the lamp.
19. Describe the relationship between the phototransistor and the lamp.
20. Explain how the phototransistor can be utilized as a normally open digital input.
21. Explain how the phototransistor can be utilized as a normally closed digital input.
Conclusion
1. Examine the wire diagram on the mini switch and describe how the diagram
relates to the concepts of normally open and normally closed.
2. If computers only understand digital signals, then how is a computer able to
interpret the analog signals coming from the interface?
3. Why does resistance decrease as the NTC Resistor becomes warmer?
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