An OR gate is a logic gate where the output goes HIGH (or “1”) if any of its inputs are HIGH. So if A OR B is HIGH, the output Q also becomes HIGH.
The logic or Boolean expression for an OR gate is which means:
If A or B is true, then Q is true
OR gates can have more than two inputs. But no matter how many inputs it has, it will always give out a HIGH or logic “1” if one of its inputs is HIGH.
2-input OR Gate Truth Table
|Input A||Input B||Output Q|
3-input OR Gate Truth Table
|Input A||Input B||Input C||Output Q|
IC Alternatives with OR Gates
- 4071: Four 2-input OR gates
- 4075: Three 3-input OR gates
- 74HC32: Four 2-input OR gates (HC is the family, can also be LS/HCT/…)
- 74HC4075: Three 3-input OR gates (HC is the family, can also be LS/HCT/…)
These should all be available as hobbyist-friendly through-hole chips. Just make sure you buy the DIP package version.
Example Circuit: Testing an OR gate
Below is a simple practical circuit you can build to test how this gate works. A Light-Emitting Diode (LED) turns on when you press either of the buttons A OR B. The circuit demonstrates the basic operation of an OR gate.