XOR GATE Educational Circuit Board
Code B07P1Y8C5F
- 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 an XOR (exclusive OR) gate, whose output is HIGH only when its two inputs are different. It lets students test the truth table by hand and see why XOR is central to the way computers add numbers. It suits students of digital electronics, computer science and 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.
An XOR gate gives output 1 when exactly one of its two inputs is 1, and 0 when both inputs are the same. Its expression is Y = A ⊕ B = A′B + AB′. The truth table reads: 0 and 0 give 0; 0 and 1 give 1; 1 and 0 give 1; 1 and 1 give 0. This 'different means 1' behaviour makes XOR the heart of binary addition. In a half adder, the sum bit is A ⊕ B and the carry bit is A·B, so 1 + 1 gives sum 0 and carry 1, which is binary 10. XOR is also used for parity checking, where it detects whether a group of bits has an odd number of 1s. The 7486 IC contains four XOR gates. The two-way switches used for staircase lights in Indian homes follow XOR logic: flipping either switch changes the state of the light.
Make it yourself
Make an XOR 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
Fit the CD4011, connect its supply pins to the rails as shown in its datasheet, and plan which of its four NAND gates you will use for each step.
Wire the input switches so ON connects each input to positive, with a 10 kΩ resistor from each input to negative for a clean 0, and an input LED with its resistor on each.
- Gate 1
Feed A and B into the first NAND gate and call its output N.
- Gate 2
Feed A and N into the second NAND gate. Gate 3: feed B and N into the third NAND gate.
- Gate 4
Feed the outputs of gates 2 and 3 into the fourth NAND gate; its output is A XOR B.
Connect that output through the 10 kΩ resistor to the transistor's base, with the output LED and its resistor between the positive rail and the collector, so the chip does not have to supply the LED current.
- Try all four combinations
The output LED should light only when the two switches are different.
Measure the voltage at N and at the outputs of gates 2, 3 and 4 for each combination, and fill in a table that proves the circuit step by step.
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; the board never needs mains power.
- Touch a grounded metal object before handling CMOS chips, and never leave their inputs floating.
- Check the chip's notch before switching on, and switch off if it gets warm.
- Solder only with an adult.
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 is wrong for one combination
One of the four gates is wired to the wrong pins. Measure N and the outputs of gates 2 and 3 for that combination and compare them with your table to find the faulty step.
The LEDs flicker or change on their own
An input is floating. Check the pull-down resistors and the wires from each switch, since all four gates of the chip are in use.
Nothing lights at all
Check that the chip's supply pins are connected the right way round and that the battery is fresh.
The output LED is very dim
The chip is probably driving the LED directly. Use the transistor driver as described, or fit a larger LED resistor.
Exhibition day
How to present it
A running order for the exhibition table or the practical, step by step.
Go through all four input combinations and highlight that equal inputs always give 0.
Show a half adder on the chart and work out 1 + 1 in binary.
Use the staircase light example to explain XOR in everyday terms.
Compare the XOR truth table with the OR table to show the one row where they differ.
Practice
Viva questions
Practice questions on this model, with short answers. Try each one aloud before you open the answer.
When is the output of an XOR gate HIGH?
When the two inputs are different, that is, one is 0 and the other is 1.
Write the Boolean expression for XOR.
Y = A ⊕ B = A′B + AB′.
Where is the XOR gate used in a half adder?
It produces the sum bit, while an AND gate produces the carry bit.
How is XOR different from OR?
They differ only when both inputs are 1: OR gives 1, but XOR gives 0.
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 XOR gate built from NAND gates
- Logic gates and the meaning of 'exclusive OR'
- Boolean expression, symbol and truth table of XOR
- Building XOR from four NAND gates, with the expression at each step
- Circuit diagram and construction
- Observation table: inputs, in-between voltages and output
- Uses of XOR: the half adder, parity checking and staircase switches
- 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 an XOR gate project suits your class and the chapter on logic gates or Boolean algebra.
- Read the listing for the supply the board needs; do not assume a battery or report is included.
- Practise explaining how XOR gives the sum bit in binary addition, which examiners like to ask.
- Keep the box for transport so the switches are not damaged.
- 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, test all four input combinations against the truth table.
Next steps
Take it further
Ways to turn this model into a bigger investigation or a stronger exhibition entry.
Add a CD4081 AND gate for the carry bit and turn the board into a half adder that adds two one-bit numbers.
Wire the two two-way switches and the bulb as a staircase circuit and show that it follows the XOR pattern, or XNOR depending on how you label the switch positions.
Use XOR gates to build a parity checker for a three-bit number and explain how it catches a single wrong bit.
Audience
Who it suits
Class 11 and 12 computer science and physics students, and diploma or engineering labs in digital electronics and computer organisation.
- 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
