Turn descriptions of alarms, lights and machines into expressions, truth tables and circuits, and use logic in program conditions.
What you will learn
- Write an expression from a description
- Complete its truth table
- Choose the right circuit for a system
- Use AND, OR and NOT in program conditions
From words to logic
A logic problem describes a system.
Pick out each input (given a letter), then the words that join them.
- "and", "both" → AND
- "or", "either" → OR
- "not", "unless", "except when" → NOT (with AND)
- "but not while" → AND NOT
A fan (Q) turns on when the room is hot (A) and the window is not open (B): Q = A AND NOT B.
Check by testing a row or two against the description: hot and window shut gives A = 1, B = 0, so Q = 1. Good.
The rest of this lesson and its 7 practice questions are locked.
In this lesson
- From words to logic
- Design and test
- Try it: Describe a system
7 practice questions, marked as you go; about 25 minutes in all.
Key terms
And, Either, Unless, Except when, But not while
In this unit: Boolean logic
AND, OR, NOT and XOR gates, truth tables, expressions and circuits, built by hand in an interactive gate builder and used to describe real systems.
- Logic gates and truth tables
- Combining gates
- Logic for real systems