- Physics
- Class 1 to 9
OR GATE (Logic Gate) Educational Circuit Board
Code B07LD2ZZ54
- Paid for and delivered by Amazon. The current price and the delivery date for your PIN code are shown there.
- Sold by Gurukul Technicals Institute, Delhi.
- Need a different topic, a custom version or a school order? Ask on WhatsApp.
In this project guide
Physics
About this model
This OR gate board lets students set its inputs and watch the output turn ON as soon as any one of them is ON. It makes the "any one is enough" rule of digital logic easy to see, the same rule used wherever one of several signals should start an action.
How it works
The science behind it
The idea the model demonstrates, in words you can use in your report and when you explain it.
In an OR gate the output is 1 if any one or more inputs are 1, and 0 only when every input is 0. In Boolean algebra this is written Y = A + B, where + means OR, not addition, so 1 + 1 = 1 in Boolean logic. Reading the two-input truth table row by row: inputs 00 give 0, while 01, 10 and 11 all give 1. Think of two switches side by side in parallel, feeding one lamp: closing either switch completes the circuit. A simple electronic OR gate can be built from two diodes and a resistor: whichever input is high passes current through its diode to the output, while the diodes stop the inputs from feeding into each other. The 7432 IC contains four OR gates. A doorbell that rings from either the main gate button or the flat door button is an OR gate in daily life.
Make it yourself
Make an OR gate circuit board yourself
Build your own version from scratch, or use the steps to understand how the ready-made model is put together before you present it.
What you need 8
Step by step 8 steps
- Show the idea first
Put two switches side by side (in parallel) and connect them with the bulb and cells. Closing either switch lights the bulb.
On the breadboard, connect each push button from positive to its own input line, A or B.
Connect a green LED with a 1 kΩ resistor from each input line to negative, so it shows when that input is 1.
Connect a diode from each input line to the output point Y, with the striped end (cathode) towards Y.
Connect the red output LED and its 470 Ω resistor in series from Y to negative, long leg towards Y; this LED shows the OR output.
Press neither, then A, then B, then both. The output LED lights in every case except when neither is pressed.
Write the truth table and Y = A + B on the chart, noting that 1 + 1 = 1 in Boolean logic.
Label the board and add the car example: the inside light comes on when either door is open.
Read this first
Safety first
Go through these points before you build or switch anything on. Younger students should do this with an adult.
- Use cells only; never an adapter you have opened.
- Every LED needs its series resistor.
- If you solder the board, do it with an adult and let the joints cool before touching them.
- Take the cells out when storing the board so they cannot leak.
Troubleshooting
If something does not work
The usual problems with this model and how to fix them. Open a problem to see the fix.
The output LED is on with no button pressed
A button may be stuck closed, or a stray wire or solder bridge joins an input line or Y to positive. Look at the input LEDs: if one is lit with no button pressed, that input is the problem.
Pressing A lights B's input LED too
B's diode is the wrong way round, letting current flow back into input B. The stripe must face the output.
The output LED is dim
The diode drops about 0.7 V. Use fresh cells, or a slightly smaller output resistor (not below 220 Ω).
The bulb version needs both switches to light
The switches are in series. Rewire them side by side so each can complete the circuit on its own.
Exhibition day
How to present it
A running order for the exhibition table or the practical, step by step.
Show all four input combinations and point out that 11 also gives 1, unlike an XOR gate.
Draw a lamp fed by two parallel switches and show that it matches the board row by row.
Explain why 1 + 1 = 1 in Boolean algebra, a favourite viva question.
Give a real OR-type example, such as a car's inside light that comes on when any door opens.
Practice
Viva questions
Practice questions on this model, with short answers. Try each one aloud before you open the answer.
If both inputs of an OR gate are 1, what is the output?
The output is 1, because an OR gate needs only one input to be 1.
What does the + sign mean in Y = A + B?
It stands for the OR operation, not ordinary addition, which is why 1 + 1 = 1 in Boolean algebra.
Give an electrical analogy for an OR gate.
A lamp controlled by two switches wired in parallel: closing either switch, or both, lights the lamp.
How is an OR gate different from an XOR gate?
An OR gate gives 1 when both inputs are 1, but an XOR gate gives 0 in that case.
Project file
Project file outline
The headings of the project file, in order. Give each heading its own section and write it in your own words.
Free ebook: Writing a Science Project FileContents
- Aim: to verify the truth table of an OR gate
- Introduction: logic gates and Boolean algebra
- The OR gate as two switches in parallel
- Materials and circuit diagram of the diode OR gate
- Theory: Y = A + B and how the diodes keep the two inputs apart
- Procedure: pressing the buttons in each combination
- Truth table for Y = A + B: expected and observed
- Real-life uses: car door lights and alarms with several sensors
- Conclusion: OR compared with AND
Buying checklist
Before you buy
What to check before you order the model.
1Check these first
- Logic gates appear in senior physics and in computer science; check which your class needs.
- Read the listing for the power source and whether batteries are included.
- Test all four input combinations straight away, and again before the exhibition.
- If you are showing several gates, put their truth tables on one chart so visitors can compare.
- Store the board in its box so the buttons are not damaged.
- Check the delivery date for your PIN code on the marketplace, and order well before the exhibition or practical.
- Practise explaining it. Judges ask what the model shows and why; knowing the science matters as much as the model. The viva questions above are a good place to start.
Next steps
Take it further
Ways to turn this model into a bigger investigation or a stronger exhibition entry.
Add a transistor NOT gate after the OR to make a NOR gate, and compare the truth tables.
Make a three-input OR gate for a model alarm with three window sensors.
Measure the output voltage for each combination and explain why it is about 0.7 V below the battery voltage.
Audience
Who it suits
A good fit for senior secondary students meeting Boolean algebra in computer science or physics, and for anyone starting out with digital circuits.
- ClassClass 1 to 9
- SubjectPhysics
Free to read
Free ebooks for this topic
Free PDF ebooks from Gurukul Technicals Institute on the science, the making and the presenting of projects like this one.
- Free PDF ebook
Electricity and Magnetism Experiments
Hands-on experiments with cells, wires, bulbs and magnets
- Free PDF ebook
Physics Working Models Explained
Twenty classic models, how each works and how to make it
- Free PDF ebook
Your Science Exhibition Guide
Choose a project, build it, present it and answer the judges with confidence
