# xor gate only use diodes

Discussion in 'Electronics Homework Help' started by palahasan, Oct 28, 2014.

1. ### palahasan

17
1
Oct 28, 2014
Can you send xor gate only use diodes in isis,please?It is my homework.I made it but it didn't work.

2. ### KrisBlueNZSadly passed away in 2015

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Nov 28, 2011
Hi palahasan and welcome to Electronics Point.

I've moved this thread to the homework help forum. Please post homework questions there.

Do you understand the basic principle behind the circuit above? Do you know how it produces a voltage across the output terminals only when the input terminals are 1,0 or 0,1 but not when they are 0,0 or 1,1?

How did you test it? You need to apply defined high and low signals at the inputs. The best way would be to use two SPDT (aka SPCO) switches, one for each input. Each switch needs to connect its input to either 0V (low) or some positive voltage (high). And the output can be fed into an LED with a current limiting resistor.

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3. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Whether that circuit has an XOR function depends on your definition of what constitutes a logic level.

Another almost equivalent circuit would be to connect the inputs directly to the second part of this circuit (the bridge rectifier).

A third option is to simply pass the two inputs directly to the outputs.

In some respects they share the same functionality. What they also share is that the definition of he input logic level differs from the definition of the output logic level. And as I said, if you can define what constitutes a valid logic level you can free yourself of limitations imposed by practicalities like having to make something usefully functional.

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4. ### KrisBlueNZSadly passed away in 2015

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Nov 28, 2011
Yes true Steve. The output cannot actually be a logic level; it's a voltage difference measured between the output points, and the bridge rectifier is just there to make sure that difference always has the same polarity. But we're not supposed to give away the solution so quickly!

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5. ### palahasan

17
1
Oct 28, 2014
Thank you for your answers.I understood your answers.I made the circuit to isis but led isn't work.

6. ### palahasan

17
1
Oct 28, 2014
Why doesn't work?I didn't understand.

7. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Here, try the simple version

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8. ### palahasan

17
1
Oct 28, 2014
Is it correct? V1 and V2=1 but Vout=1

9. ### KrisBlueNZSadly passed away in 2015

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Nov 28, 2011
That's the right idea. If you want a real circuit that will work, you need to define the inputs, you need a current limiting resistor for the LED, and you should remove the earth at the LED's cathode.

10. ### palahasan

17
1
Oct 28, 2014
Thank you very much for your help.

11. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Now you can extend your analysis to the original circuit. It is doing something a little tricky, can you figure out what that is? And is it important?

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12. ### palahasan

17
1
Oct 28, 2014
Problem is Vout in original circuit.The current isn't going to one leg of Vout(led).Do I think correct?

13. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Nope.

edit: Try placing some voltages on the inputs (on the schematic) and determine what all the other node voltages will be (do it without a load on the output). You may want to assume some values for the resistors and to assume the diodes are ideal.

14. ### palahasan

17
1
Oct 28, 2014
V1 and V2:1 but Vout:1

15. ### KrisBlueNZSadly passed away in 2015

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Nov 28, 2011
Are you saying that in that circuit as shown, V1 and V2 are both 1, and Vout is 1? If that's what you mean, then that's wrong. V1 (from SW1) is 1 (high), but V2 (from SW2) is 0 (low) in that circuit as shown. Therefore the output SHOULD be 1 (LED illuminated).

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16. ### KrisBlueNZSadly passed away in 2015

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Nov 28, 2011
V2 is 0 because SW2 is switched to the downward position.

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17. ### palahasan

17
1
Oct 28, 2014
My last question;is it possible without switches,only diodes?

18. ### KrisBlueNZSadly passed away in 2015

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Nov 28, 2011
How are you going to get your input states into it?

Your circuit has two inputs. They need to be driven with logic levels - either high (1) or low (0).

That's what the switches are for. If you have some other source of logic levels, you don't need switches. But to make that circuit usable, you have to define what the inputs are driven from. Just calling them "V1" and "V2" doesn't give you enough information about what is driving those inputs. That's why I drew the battery and the switches.

If you have some other source to supply the V1 and V2 inputs, show us what it is. If it's the outputs from two logic ICs, then the circuit will work, as long as the "OUT1" and "OUT2" connection points are connected to a fully floating device such as an LED (with current limiting resistor).

In other words, if you don't want the battery and switches, what will you replace them with? Draw a circuit with that, and we can tell you if it will work. Or you can simulate it yourself.

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19. ### palahasan

17
1
Oct 28, 2014
You're right.Thank you for informing me.

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