78 lines
2 KiB
Markdown
78 lines
2 KiB
Markdown
---
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tags:
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- Logic
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- Electronics
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- binary
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---
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# Logic circuits
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> Now that we are familiar with the individual [logic gates](Logic_gates.md) and their truth conditions we are in a position to create **logic circuits**. These are combinations of logic gates controlled by inputs that can provide a range of useful outputs. The output of a logic gate is a function of the truth-values of the individual gates and their connections to each other.
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## Basic example
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In the below circuit we have the following gates connected to two inputs with one output, moving through the following stages:
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1. `AND`, `NOT`, `NOT`
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1. `AND`, `NOR`
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This is equivalent to the following truth table:
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````
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A B Output
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_ _ _____
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0 0 0 (1)
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1 0 1 (2)
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0 1 1 (3)
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1 1 0 (4)
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````
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*Line 1 of the truth table*
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*Line 2 and 3 of the truth table (equivalent to each other)*
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*Line 4 of the truth table*
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## Applied example
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With this circuit we have a more interesting applied example.
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It corresponds to an automatic sliding door and has the following states
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* a proximity sensor that opens the doors when someone approached from outside
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* a proximity sensor that opens the doors when someone approaches from the inside
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* a manual override that locks both approaches (inside and out) meaning no one can enter of leave
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Here's a visual representation:
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The following truth table represents this behaviour, with A and B as the door states, C as the override and X as the door action (0 = open, 1 = closed)
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````
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A B C X
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_ _ _ _
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0 0 0 0
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1 0 0 0
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0 1 0 0
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1 1 0 0
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0 0 1 0
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1 0 1 1
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0 1 1 1
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1 1 1 1
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````
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*Automatic door sensor with manual override*
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