Pneumatic and Electronic Logic Gates
Pneumatic Valves: Logic
Pneumatic valves can perform logical functions, similar to logic gates. There are two main types:
A) “OR” Valve (Selector or Double-Acting)
Used when you want to drive a cylinder from two positions interchangeably. Air enters through “X”, the piston is moved to “Y”, and exits along “A”. (See diagram)
B) “AND” Valve (Simultaneity)
Used when a cylinder is operated from two different points *simultaneously*. Air must enter through *both* “X” and “Y” because it creates a blockage. (See diagram)
Electronics: Analog and Digital Signals
An electrical signal represents a change in magnitude over time. All circuits operate with electrical signals.
- Analog: The signal changes continuously over time, passing through all intermediate values.
- Digital: The signal varies in discrete steps, taking only specific values.
The binary digital signal can only take two values (1 and 0). These two values form the basis for the design of multi-digital electrical circuits. Each of these values is called a bit. This is the system that computers use to process information. These two values do not represent binary numbers but rather different states of a device.
Truth Table of a Circuit
Both the inputs and outputs can only be in two states: voltage present (1) or no voltage (0).
The truth table of a digital circuit is a table that represents all the states in which the inputs and outputs can be found.
To create a truth table, follow these steps:
- Create a row with all the variables, both inputs and outputs.
- Below the inputs, list all possible combinations of zeros and ones.
- Looking at the circuit diagram, go row by row to determine if the status of the inputs will turn on light bulbs or not, setting the appropriate output value (0 or 1).
Logic Function of a Circuit: Boolean Algebra
Boolean algebra is a mathematical theory based on the binary system, whose postulates can be applied to all types of elements working with two possible states.
The logic function of a circuit is a mathematical expression that relates the inputs and outputs. From it, we can deduce a circuit’s operation.
The logic function for an output (S) will be a mathematical expression consisting of a sum of products.
When a table has more than one output, there will be a logic function for each output.
Logic Gates
A logic gate is an electronic circuit that provides a digital signal at its output when its inputs also receive digital signals. The output signals depend on the input signals.
Types of Logic Gates:
A) OR Logic Gate
Function: Sum. Equivalent to two switches mounted in parallel. Activating one button, the other, or both allows current to flow.
The output of an OR logic gate is in state 1 if *any* input is in state 1. (See diagrams)
B) NOT Logic Gate (Inverter)
Function: Negation. It has only one input and one output. It is used to reverse or negate a signal; that is, if we input a 1, the output will be a 0. It is very useful in circuit design.
The output of a NOT logic gate is in state 1 *only* if the input is in state 0, and it is in state 0 if the input is in state 1. (See diagram)
C) NOR Logic Gate
Function: An OR gate followed by a negation. The bulb lights only when *both* switches are off. (See diagrams)
The NOR function produces an output signal only when *no* input signal is triggered.
D) NAND Logic Gate
Function: An AND gate followed by a negation. The bulb only lights up when *any* of the switches A and B are open. It is necessary to close *both* switches to turn off the bulb. (See diagrams)
The NAND function produces an output signal unless *all* input signals are activated.