The OR Logic Gate is another computer circuit providing a TRUE output based on at least one input data value having a closed state. A basic OR Logic Gate electric circuit schematic diagram is shown in Figure 7-2. The circuit schematic diagram on the left shows one pushbutton switch closed and the other one open. The output for this pushbutton switch combination is TRUE, indicated by the LED being on. When both switches are open, as shown in the right circuit schematic diagram, the LED will be off. In summary, if at least one of the pushbutton switches is TRUE, the OR Logic Gate’s output will be TRUE. Therefore, the OR Logic Gate provides a TRUE output when either input is TRUE. This is different from the AND gate, which requires both inputs to be TRUE. To experiment with a basic OR Logic Gate circuit, the Fritzing wiring diagram shown in Figure 7-3 can be built on a breadboard.
Figure 7-2. Circuit schematic diagram for the OR Logic Gate controlling an LED
Figure 7-3. A basic OR Logic Gate circuit Fritzing wiring diagram
TECH NOTE
If you need an OR Logic Gate for an electronics project, simply wire two or more switches in parallel.
Just like the other logic gates discussed in the OR Logic Gate has a special circuit symbol as well, shown in Figure 7-4. The truth table (TT) shows the logic gate operation. Figure 7-5 is an OR Logic Gate TT.
Figure 7-4. The OR Logic Gate circuit symbol
Figure 7-5. The OR Logic Gate Truth Table
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