I am sure you must be familiar with an OR Gate, its Truth Table, Logic symbol, and its working. But do you know, you can build your own OR Gate on Breadboard? So in this post, you will learn how to make an OR Gate using Diodes on Breadboard.
**Read Similar Article: And Gate using Diodes
OR Gate Symbol and Truth table
OR means “to add”. There are two inputs and one output in an OR Gate. Only when both inputs are zero, the output is zero. Output is 1 in all other cases. Given below is the truth table of an OR gate.
You can also watch the video below for quick reference:
Components required:
1. 1N4007 Diode X 2
2. 1k Resistor
3. LED
4. 9 Volt Battery
5. Connecting Wires
If you are a beginner and want to know about breadboards in detail, read: How to Use a Breadboard in 5 Easy Steps
Circuit Diagram of OR gate using diodes
Given above is the circuit we are going to build on Breadboard.
Working
NOTE: When the P-terminal of a Diode is at a higher potential (>.7v) than its n-terminal, the diode acts like a short circuit. And when the n terminal is at a higher potential, Diode acts as an open circuit.
**from circuit diagram
CASE 1: Input A=0, Input B= 0
In this case, the p-terminal of both diodes is at 0 volts w.r.t n-terminal which is <.7v and hence acts like an open circuit. Thus no current flow from 1k resistor, then LED to Ground. Hence there is no voltage across LED and it remains off i.e, 0 at the output.
CASE 2: Input A=0, Input B= 1
In this case, p-terminal of diode A is at 0 volts w.r.t n-terminal which is <.7v and hence acts like an open circuit. But p-terminal of diode B is at a higher potential than its n-terminal which is >.7v. Thus all current flow from 1k resistor, then LED to Ground. Hence there is some voltage across LED and it turns on i.e, 1 at the output.
CASE 3: Input A=1, Input B= 0
In this case, p-terminal of diode B is at 0 volts w.r.t n-terminal which is <.7v and hence acts like an open circuit. But p-terminal of diode A is at a higher potential than its n-terminal which is >.7v. Thus all current flow from 1k resistor, then LED to Ground. Hence there is some voltage across LED and it turns on i.e, 1 at the output.
CASE 4: Input A=1, Input B= 1
In this case, p-terminal of both diodes is at higher potential w.r.t n-terminal which is >.7v and hence acts like short circuits. Thus all current flow from 1k resistor, then LED to Ground. Hence there is some voltage across LED and it turns on i.e, 1 at the output.
** Hence we get 0(LED is off) at the output only when both the inputs are 0 as given in Truth Table.
Simulation:
Note: Before building the circuit on a breadboard, it is first simulated on “Every circuit” app. You can download the app from here.
** The circuit is exactly similar to what is given above.
** Slideshow
CASE 1: Input A=0, Input B= 0 , Output=0 (LED is OFF)
CASE 2: Input A=0, Input B= 1, Output=1 (LED is ON)
CASE 3: Input A=1, Input B= 0, Output=1 (LED is ON)
CASE 4: Input A=1, Input B= 1, Output=1 (LED is ON)
Let’s Make it!
1. Place the two diodes on the breadboard. N-terminal is the silver portion, and P-terminal is the Black portion.
2. Connect the N terminal of the Diodes together using wire as shown below:
3. Connect two jumper wires, each at respective p-terminal of the diodes indicating input Logic.
4. Connect the Battery to the breadboard as shown.
5. Connect the resistor from the n terminal of the Diodes to the Ground through LED.
CASE 1: Input A=0, Input B= 0 , Output=0 (LED is OFF)
In this case, p-terminal of both diodes is at 0 volts w.r.t n-terminal which is <.7v and hence acts like an open circuit. Thus no current flow from 1k resistor, then LED to Ground. Hence there is no voltage across LED and it remains off i.e, 0 at the output.
CASE 2: Input A=0, Input B= 1, Output=1 (LED is ON)
In this case, p-terminal of diode A is at 0 volts w.r.t n-terminal which is <.7v and hence acts like an open circuit. But p-terminal of diode B is at a higher potential than its n-terminal which is >.7v. Thus all current flow from 1k resistor, then LED to Ground. Hence there is some voltage across LED and it turns on i.e, 1 at the output.
CASE 3: Input A=1, Input B= 0, Output=1 (LED is ON)
In this case, p-terminal of diode B is at 0 volts w.r.t n-terminal which is <.7v and hence acts like an open circuit. But p-terminal of diode A is at a higher potential than its n-terminal which is >.7v. Thus all current flow from 1k resistor, then LED to Ground. Hence there is some voltage across LED and it turns on i.e, 1 at the output.
CASE 4: Input A=1, Input B= 1, Output=1 (LED is ON)
In this case, p-terminal of both diodes is at higher potential w.r.t n-terminal which is >.7v and hence acts like short circuits. Thus all current flow from 1k resistor, then LED to Ground. Hence there is some voltage across LED and it turns on i.e, 1 at the output.
** Hence we get 0(LED is off) at the output only when both the inputs are 0 as given in Truth Table.
