WEEK

A summary of some of the ideas presented last week, the water model.

We are going to explore electricity and electronics.

GOALS:

• Understand how to formulate a logic problem.
• To learn how to use logic gates to do logic problems.

This week we will start what I hope will be a straightforward use of electronics. First we need to understand what we mean by logic problems. Perhaps the best way to begin is to examine often used statements that contains all the elements required to do logic and to realize that we use logic to solve everyday problems. Consider the following statement:

If I finish my homework AND the sun is shining THEN I will play soccer.

We know we are making a decision based on some input. We need to evaluate the two conditions in order to reach a conclusion.

Condition 1: Homework done ?

Condition 2: Sun shining ?

Conclusion: Playing soccer ?

The facts, conditions and the conclusions, can be stated in terms of one of two possibilites: YES or NO.

Logic is the statement and solution of problems that involve conditions and conclusions that have two possible values. These are connected by logic operators. The word AND signifies the type of logic that we are applying.

For our purposes we need to understand that the two condition can be represented in a few different ways as follows.

 YES NO True False On Off 5 Volts 0 Volts

A convenient way to evaluate or display the information contained in the problem is in the form of a truth table as shown below.

 Homework done Sun shining Play soccer T T T T F F F T F F F F

The truth table given above provides the solution for a problem where AND is the logical operation. A similar problem and table could be constructed using the OR logical operator. In addition we will introduce the NOR and the NAND logical operations during our lab meeting.

Hopefully, you are comfortable with the everyday use of logic and understand how the above table was constructed based on the logic problem stated. This week we will work with electronic logic gates, which allow us to formulate and solve logic problems using electronics. To set the stage, imagine that you need to design a quiz show set for an activity for a club. Your job is to build the buzzer system. If a contestant hits his/her buzzer you would like to have a noise sound and a light indicate the contestant that hit the buzzer. You would also like to have the system respond only to the first person that presses the button and ignore subsequent presses. To build this system you need electronics that can solve a logic problem. To formulate the problem we need to represent the conditions and conclusion as electronic signals. A common convention is to let a 5 Volt signal indicate at YES state and a 0 Volt signal represent a NO state. This is the convention we will use in the lab. We will accept a range of possible values to make the implementation easier.

 YES NO TRUE FALSE greater than 2.5 Volts less than 1 Volt

Our goal will be to apply the two possible inputs (T/F) to electronic logic gates and read the conclusion using a voltmeter. A more sophisticated method will be to use LED's as indicators for the various conditions and conclusions. This will become clearer as we build the circuits during the lab.

QUIZ *******

QUIZ *******

In order to receive a grade of A you must successfully complete the lab portion of the course, read prelab material, and pass the lab quiz. In order to pass you must get 75% of the questions correct.

In order to receive a grade of B you must successfully complete the lab portion of the course. The quiz is optional. For fun feel free to try the quiz.

You are not allowed to consult with other students while taking the quiz. You will be given a limited time period to complete the quiz. You may refer to any written material.

You may take the quiz at any time during the week but only once.

The quiz will be available starting on the day you cover the material and ending one week later.

If you have troubles please discuss the difficulties with DRG.

You are not allowed to consult with other students while taking the quiz. The quiz will be available at least from lab until following lab. You will be given 30 minutes to complete the quiz and you may refer to any written material.