NOR GATE Educational Circuit Board
Code B07P327NHH
- 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
Physics
About this model
This educational circuit board demonstrates a NOR gate, a basic logic gate whose output is HIGH only when all its inputs are LOW. Changing the inputs and watching the output lets students verify the truth table for themselves. It is a good project for anyone learning digital electronics or Boolean algebra.
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.
A NOR gate is an OR gate followed by a NOT gate. Its Boolean expression is Y = (A + B)′, read as 'A OR B, complemented'. For two inputs, A = 0 and B = 0 gives Y = 1, while any input at 1 gives Y = 0; in other words, the output is 1 only when neither input is 1. NOR is called a universal gate because every other gate can be built from NOR gates alone. Joining both inputs of a NOR gate gives a NOT gate. A NOR followed by a NOT (another NOR) gives OR. Inverting both inputs before a NOR gives AND, by De Morgan's theorem, (A′ + B′)′ = A·B. Among standard logic ICs, the 7402 contains four two-input NOR gates. The Apollo Guidance Computer, which helped astronauts land on the Moon, was built almost entirely from NOR gates, which shows how much can be made from this one simple gate.
Make it yourself
Make a NOR 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 9
Step by step 8 steps
Wire each input switch so that ON connects its input line to the positive rail, and fit a 10 kΩ resistor from each input line to negative so that OFF gives a clear 0.
Connect each input line through a 10 kΩ resistor to the base of its own transistor, and both emitters to the negative rail.
Join the two collectors and connect them to the positive rail through the 1 kΩ resistor; this joined point is the output Y.
Connect the red output LED from Y to negative (longer leg towards Y), and an input LED with its 1 kΩ resistor from each input line to negative.
Switch on with both inputs at 0: neither transistor conducts, so Y stays HIGH and the output LED lights.
Turn on A, then B, then both, and notice that any 1 at the inputs switches on a transistor, which pulls Y down to 0.
Measure the voltage at Y for all four input combinations and write it beside the truth table.
Explain on a chart that the two transistors side by side act as the OR, and the pulled-up output that goes LOW acts as the NOT that follows it.
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 only the 9 V battery; logic boards never need mains power.
- Keep the 10 kΩ base resistors in place, as a base connected straight to the supply can destroy the transistor.
- Switch off before rewiring anything on the breadboard.
- Solder only with an adult and let the joints cool before handling.
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 stays on whatever the inputs
The transistors are not switching. Check their pin order and base resistors, and that each switch really connects its input to positive.
The output LED never lights
Check the LED's direction and the 1 kΩ pull-up resistor; without the pull-up there is nothing to make the output HIGH.
An input LED glows faintly with its switch off
The 10 kΩ pull-down on that input is missing, so the input line is floating. Fit it between the input line and negative.
With the CD4001 the outputs change randomly
Unused CMOS inputs are floating. Tie every unused input to negative, and give the inputs you switch pull-down resistors.
Exhibition day
How to present it
A running order for the exhibition table or the practical, step by step.
Switch the inputs through all four combinations and let the judges fill in the truth table themselves.
Show how a NOR gate with its inputs joined works as a NOT gate.
Write the Boolean expression and De Morgan's theorem on the chart.
Mention the Apollo computer to show that NOR gates alone can build a complete computer.
Practice
Viva questions
Practice questions on this model, with short answers. Try each one aloud before you open the answer.
What is the Boolean expression for a NOR gate?
Y = (A + B)′, that is, the complement of A OR B.
When is the output of a NOR gate HIGH?
Only when all its inputs are LOW (0).
Why is NOR called a universal gate?
Because any logic gate, and therefore any digital circuit, can be built using only NOR gates.
How do you make a NOT gate from a NOR gate?
Join both inputs together; the output is then the complement of the single input.
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 a NOR gate
- Digital signals and the logic levels 0 and 1
- OR and NOT gates, and NOR as OR followed by NOT
- Symbol, Boolean expression and truth table of NOR
- Circuit diagram of the transistor NOR gate and how it works
- Observation table: inputs, output LED and measured output voltage
- NOR as a universal gate: making NOT, OR and AND
- Conclusion and precautions
Buying checklist
Before you buy
What to check before you order the model, and what to do when it arrives.
1Before you order
- Check that a NOR gate project suits your class and the chapter on logic gates or digital electronics.
- Read the listing for the supply the board needs; do not assume a battery or a report is included.
- Practise explaining why NOR is called a universal gate, a common viva question.
- Keep the box so the switches are not broken in a school bag.
- Check the delivery date for your PIN code on the marketplace, and order well before the exhibition or practical.
2When it arrives
- When it arrives, run through all four input combinations and check them against the truth table.
Next steps
Take it further
Ways to turn this model into a bigger investigation or a stronger exhibition entry.
Use the gates of a CD4001 to build NOT, OR and AND from NOR gates alone, one at a time, and verify each truth table.
Add a third transistor in parallel to make a three-input NOR gate and write its truth table.
Build a set-reset latch from two NOR gates and show how it remembers which button was pressed last.
Audience
Who it suits
Class 11 and 12 computer science and physics students learning Boolean logic, and diploma or engineering digital electronics labs.
- 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.
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Your Science Exhibition Guide
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Writing a Science Project File
How to write the report, from the cover page to the bibliography
