Activity1.2.2h Potentiometers

Introduction

Have you ever wondered how the volume control on your iPod works? Maybe there is a dimmer switch on a light in your house or classroom. How are lights and sounds able to experience such minute changes?

In this activity you will learn about a special resistor called a potentiometer. You will use the potentiometer’s variable control to write a program. You will also develop an understanding of analog sensing devices.

Equipment

  • Computer interface
  • Potentiometer
  • Rack
  • Wires
  • Gearbox

Background

A potentiometer is a type of variable resistor. Resistors are used to control the value of voltage and current in an electronic circuit. Resistors can have a fixed resistance value or one that can be changed; hence, they are generally classified as fixed or variable resistors.

Variable resistors are used when it is necessary to frequently change the value of resistance in a circuit. These devices have a sliding/rotating contact arm that is in contact with a strip of resistive material. A potentiometer has three contacts. The resistance between the center shaft and the two outside contacts changesas the shaft of the potentiometer is rotated.

Figure 1

In ROBOPro the interface measures the resistance between the center and one of the outside contacts of the potentiometer. The interface reports the resistance as an analog value between 0 – 1028. The potentiometer is connected to either EX or EY.

Figure 2

Procedure

  1. Set up your fischertechniks components according to Figure 4.

Figure 3

Figure 4

  1. Connect the potentiometer to EX.
  1. A potentiometer only rotates 270 degrees, so you must place the potentiometer and the rack at a centered starting point.
  1. After the potentiometer is centered, run the diagnostic program and determine the values and directional information for the potentiometer.
  1. Instruct the motor to turn in one direction until the potentiometer reads a predetermined value, then change direction and instruct the motor to go the other way.
  1. You must use the Variableand Comparefunction blocks for this program.
  1. Once the program is functioning correctly, demonstrate its operation to your instructorand print out a copy of your program.

Conclusion

  1. What is the feedback in this system?
  1. Provide an example of a positional control system and an explanation of how it works.
  1. Give two examples where you might find a potentiometer (do not use the examples shared in the Introduction).

PLTW

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CIM– Unit 1 – Activity 1.2.2h – Potentiometers– Page 1