- Physics
- Ready-made model
- Class 10 to 12
AND OR NOT Logic Gates Working Model
Code B0G2T8GY41
- 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.
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In this project guide
Ready-made model
About this model
This digital electronics model demonstrates the three basic logic gates, AND, OR and NOT, and how each one decides its output from its inputs. It makes a clear investigatory project for explaining the building blocks of every computer and digital device.
What the listing says
- Digital Electronics Physics Investigatory Project
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.
Digital circuits use just two states, 1 (a voltage present) and 0 (no voltage). Switches and a bulb explain the three basic gates. An AND gate is like two switches in series: the bulb lights only when both are closed, so Y = A·B is 1 only when A and B are both 1. An OR gate is like two switches in parallel: the bulb lights when either one is closed, so Y = A + B. A NOT gate has a single input and inverts it, so 1 becomes 0 and 0 becomes 1. In simple circuits, AND and OR gates can be built from diodes and resistors, but a NOT gate needs an active device such as a transistor, because diodes cannot invert a signal. Any digital circuit can be built by combining these three gates. An emergency light that switches on only when mains power is NOT present is an everyday example of NOT logic.
Make it yourself
Make AND, OR and NOT gates from diodes and a transistor 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 9
Step by step 9 steps
Wire each input switch so its middle pin is the input, one end pin goes to positive (logic 1) and the other to negative (logic 0), and label the positions 1 and 0.
- OR gate
Connect the plain end (anode) of one diode to input A and of another to input B, join their banded ends to form the output, and connect the output through the 470 Ω resistor to an LED whose short leg goes to negative.
- AND gate
Connect the banded ends of two more diodes to the same inputs A and B, join their plain ends, and connect this junction to positive through a 1 kΩ resistor and to the long leg of an LED whose short leg goes to negative.
Check the transistor's pins in its datasheet; on the common BC547, with the flat face towards you and the legs down, they are collector, base and emitter from left to right.
- NOT gate
Connect input C through the 10 kΩ resistor to the BC547's base, its emitter to negative, and its collector to positive through the other 1 kΩ resistor; connect an LED from the collector to negative.
Switch on and work through the input combinations 00, 01, 10 and 11 for A and B, and 0 and 1 for C, writing down whether each LED is on (1) or off (0).
Compare your results with the truth tables: the OR LED lights if either input is 1, the AND LED only when both are 1, and the NOT LED always shows the opposite of C.
Build the analogy panel beside it: two switches in series with a bulb for AND, and two switches in parallel for OR.
Draw each gate's symbol, Boolean expression and truth table next to its LED.
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 the soldering iron only with an adult, rest it in its stand, and let joints cool before touching.
- Run the board on the 4.5 V cell pack only; never power it from an opened charger or anything wired to the mains.
- Check that no bare wires touch before switching on, and switch off if anything gets warm.
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 AND LED lights when only one input is 1
The diode on the other input is reversed or not soldered, so it cannot pull the output down. Check that both AND diodes have their bands towards the input switches.
The OR LED never lights
The LED is in backwards, or both diodes are reversed. For the OR gate the diodes' bands must face the output, and the LED's long leg must face the 470 Ω resistor. Turn the wrong part round and test again.
The NOT LED stays on whatever the input
The transistor may be fitted the wrong way round, or the base resistor has a dry joint. Check the pin order and resolder.
The outputs change at random
An input is left floating instead of being connected to 1 or 0. Make sure each switch's outer pins really go to positive and negative.
Exhibition day
How to present it
A running order for the exhibition table or the practical, step by step.
Show the truth table of each gate on a chart and check every row live by changing the inputs.
Use the switch analogy, series for AND and parallel for OR, so that non-science visitors can follow too.
Give everyday examples: a doorbell with buttons at two doors works like OR, and an emergency light works like NOT.
Explain how putting a NOT gate after an AND gate gives a NAND gate, the next step in digital logic.
Practice
Viva questions
Practice questions on this model, with short answers. Try each one aloud before you open the answer.
What is the truth table of an AND gate?
The output is 1 only when both inputs are 1; for the inputs 00, 01 and 10 the output is 0.
Which logic gate has only one input?
The NOT gate, which gives an output opposite to its input.
Which arrangement of switches behaves like an OR gate?
Two switches connected in parallel, because the bulb lights if either switch is closed.
Why can a NOT gate not be made with diodes alone?
A diode cannot invert a signal, so an active device such as a transistor is needed to turn a high input into a low output.
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 build AND, OR and NOT gates and verify their truth tables
- Introduction: digital signals, logic levels 1 and 0, and Boolean algebra
- Switch analogy: series switches for AND and parallel switches for OR
- How the diode-resistor AND and OR gates work
- The transistor NOT gate, and why diodes alone cannot invert
- Circuit diagrams and list of components
- Observations: truth tables recorded from the model
- Applications of logic gates in computers and everyday devices
- Conclusion and bibliography
Buying checklist
Before you buy
What to check before you order the model, and what to do when it arrives.
1Before you order
- Check where logic gates appear in your syllabus (Class 12 physics in some boards, or computer science), and confirm what your teacher expects.
- Read the listing to see how the gates are shown and what power source the model uses.
- Practise explaining why a NOT gate needs a transistor.
- Keep the box and spare cells.
- Check the delivery date for your PIN code on the marketplace, and order well before the exhibition or practical.
2When it arrives
- On arrival, test every input combination and write the truth tables yourself before the exhibition.
Next steps
Take it further
Ways to turn this model into a bigger investigation or a stronger exhibition entry.
Feed the AND output into another transistor inverter to make a NAND gate, and the OR output into one to make NOR, and record their truth tables.
Design a simple security logic, such as an alarm that sounds only when the door is open AND the system is switched on.
Verify De Morgan's laws by building NOT (A AND B) and (NOT A) OR (NOT B) and comparing the outputs.
Audience
Who it suits
Suits Class 9 to 12 students for computer science and physics projects on Boolean logic, and beginners in digital electronics.
- ClassClass 10 to 12
- SubjectPhysics
- TypeReady-made model
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
Physics Working Models Explained
Twenty classic models, how each works and how to make it
- Free PDF ebook
Investigatory Projects for Class 11 and 12
Topics, method and report structure for physics, chemistry and biology
- Free PDF ebook
Your Science Exhibition Guide
Choose a project, build it, present it and answer the judges with confidence
