A few questions about a XOR logic gate - Electronic Circuits Projects Diagrams Free

jaxx14 · 23rd December 2007, 12:51 PM

Hello.
Is XOR gate also called Exclusivbe-OR gate?
And what should i know before useing a XOR gate in a circuit. Yesterday i read a topic where someone bought logic gates and there was some complications with the high and low states. I just bought a logic gate for one of my projects, i will be haveing a 74f86 exclusive-OR logic. I wan't to have that logic chip to drive a transistor. So i would like to know how to connect the inputs. one input is should be always high, and the second input should be driven by a phototransistor. if the phototransistors signal has been cut, then the input should go Low so the output will be high. I have attached the datasheet of the 74f86 to the post. And if someone would give me a little schematic for it i would be very grateful. Cause i don't have any ideas myself right now.

ericgibbs · 23rd December 2007, 02:18 PM

hi.
The output of a 2 input XOR gate will be High when either one of the inputs is High, but NOT both.

Does this help?

In this circuit, when Vin is low [0v] then Vout is low, when Vin is High [+5v] Vout is High..

jaxx14 · 23rd December 2007, 02:59 PM

Yeah, that i have figuered out with the help of a datasheet, but thnx for the schematic. Oh and i have photodiodes not phototransistors. Well thnx, and i will be drawing my schematic some day, i hope i do it correctly.

jaxx14 · 23rd December 2007, 08:14 PM

Sry for the double post.
I came up with a schematic but i don't know if it may work like this. The D? diode should be a thyristor but i didn't have a thyristor in the component list. so i modified it a little. I hope you can correct me if there is something wrong with my schematic. Oh and there are no values because i just don't know what should the values be and what transistor to use. Any ideas are welcome.
Oh and that capacitor will be loaded by another thing, but i didn't draw it on here. Cause i don't have the schematic for that. I know i could of made a little block with Cap Charger written inside.

shaneshane1 · 23rd December 2007, 10:28 PM

Hi

im not the best when it comes to these types of schematics, but i think your diode is the wrong way around, and the transistor you have drawn is a NPN with your collector connected to +V ?

and you may be able to use a single input inverter instead of the IC you are using,because one of you inputs is always connected to +V

with an inverter the output is high(1) with the input been low, and the output is low (0) when the input is high (1)

And as for your resistor values, well the one for your base can be anything low i suppose, try 10K, 100K ?

And for the collector, it just has to suit your emitter load i think, so in your case a LED.

Roff · 23rd December 2007, 10:39 PM

Jaxx14, are you aware that you don't need an XOR, or any other logic gate, to do what you are apparently trying to do? It just makes things more difficult. That is, unless you plan to apply some other signal besides VCC to the other input of the XOR.
What exactly are you trying to do?

ericgibbs · 24th December 2007, 09:18 AM

Quote:

Originally Posted by shaneshane1

Hi

im not the best when it comes to these types of schematics, but i think your diode is the wrong way around
The diode on the ic output to the transistor base is a LED and it is the right way round.
, and the transistor you have drawn is a NPN with your collector connected to +V ?
A NPN transistor does have its collector to a +V supply.

and you may be able to use a single input inverter instead of the IC you are using,because one of you inputs is always connected to +V
He dosn't need any invertor or 7486 if he reconfigures the photodiode circuit.

with an inverter the output is high(1) with the input been low, and the output is low (0) when the input is high (1)
This is correct.

And as for your resistor values, well the one for your base can be anything low i suppose, try 10K, 100K ?
Remember the forward voltage drop across the LED, say 1.8V and the Vbe drop in the transistor, you finish up with +5V - ( 1.8 + 0.7) =2.5V across the resistor, so a 330R or 470R would be suitable.
And for the collector, it just has to suit your emitter load i think, so in your case a LED.
I dont follow what you mean.?

Hi Shane,
Sorry to pick holes in your post, but I thought you may appreciate my guidance.
Have a Happy Xmas...

shaneshane1 · 24th December 2007, 10:03 AM

Quote:

Originally Posted by ericgibbs

Hi Shane,
Sorry to pick holes in your post, but I thought you may appreciate my guidance.
Have a Happy Xmas...

the diode i was talking about was the one on one of his lower input.

as for the transistor, i now realise im incorrect, as you may have noticed from previous posts of mine

Quote:

Originally Posted by ericgibbs

And for the collector, it just has to suit your emitter load i think, so in your case a LED.
I dont follow what you mean.?

well he has a resistor on his collector?
so i thought that if he had the resistor on the collector or the emitter it would not make a difference?

because the current has to pass though the collector to the emitter?

jaxx14 · 24th December 2007, 12:55 PM

That PD? ,the photodiode is upside down yeah, cause i forgot to switch it. oh and that LEd i have there on the base, i am actually thinking of leaving that out. oh and the capacitor values may be 800microFarads and 300V. If that makes any difference. Oh and Roff i am trying to do an atomatic switch to my coilgun, before the second coil.

Brian Hoskins · 24th December 2007, 02:30 PM

I would tackle your problem in a different way. Why not use the photodiode in series with a resistor and connected across the 5V power supply? Then, connect the junction of the photodiode and resistor to an Op-Amp setup as a comparator.

This would be a much better circuit, and adjusting the point at which the comparator "trips" would be a simple matter of adjusting the reference voltage (use a variable pot). Calculating the value of the series resistor is also a simple matter, but you'd need to take a look at the datasheet for the photodiode first (to see how much current it passes for different light intensities).

If you'd like me to draw up a circuit for this and explain it to you, I will. Please let me know what photodiode you are using.

Brian

jaxx14 · 24th December 2007, 10:03 PM

Why am i using tha XOR gate? Because i have one lieing around. Oh and that photodiode is pretty old, it's a russian photodiode: fd-23k 11-78(these last numbers should be the production month and year). I have a lot of russian electronic parts. That thyristor is T122-25-12-4 the T122 is the type, 25 means 25A (continues) and 12 means 1200V, what does that 4 mean? i have no clue.

Brian Hoskins · 24th December 2007, 10:07 PM

I can't find datasheets for any of those components. If datasheetcatalog.com doesn't have them, they probably don't exist!

Brian

jaxx14 · 25th December 2007, 11:46 AM

I've allready searched them on the net and i think there aren't any datasheets for them. But those parts a pretty old, that photodiode has been made in 1978. and the T122 thyristor or SCR(should be the same thing) is also pretty old. BTW i've never found any datasheet for Russian type parts. For example take GT402I its a transistor with a pretty big capsule. i would take a picture of it but can't find my cam. Oh and for that Thyristor i found the numbers on the web, but thats was all, nothing more, only that it stands 25 A of current contiues and 1200V and thats all.

jaxx14 · 26th December 2007, 01:59 PM

Sry for the double post again, but soon i will be going to remake my schematic to a more reasonable schematic. Yesterday after going to sleep there was a flash in my head and i know how to draw what i need (i hope). I am not very good at drawing schematics from scratch, so this is pretty much my first time.

Dean Huster · 27th December 2007, 02:20 PM

Since the general subject is XOR gates, I might add the point that if you try to "widen" the number of inputs by cascading 2-input gates (XORs are generally available only in 2-input versions) as you would AND or OR gates, the exclusivity disappears. An exclusive OR gate will have the logic of "if one and only one input is HIGH, the output will be HIGH; in all other cases, the output will be LOW". Cascaded XOR gates will have the logic of "if an odd number of inputs are HIGH, the output will be HIGH; in all other cases (an even number of inputs HIGH including no inputs HIGH) the output will be LOW". Regardless of the lack of exclusivity, the latter logic is great for creating a parity generator or parity checker.

Dean

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23rd December 2007, 02:59 PM	(permalink)
jaxx14	Yeah, that i have figuered out with the help of a datasheet, but thnx for the schematic. Oh and i have photodiodes not phototransistors. Well thnx, and i will be drawing my schematic some day, i hope i do it correctly.

23rd December 2007, 10:28 PM	(permalink)
shaneshane1	Hi im not the best when it comes to these types of schematics, but i think your diode is the wrong way around, and the transistor you have drawn is a NPN with your collector connected to +V ? and you may be able to use a single input inverter instead of the IC you are using,because one of you inputs is always connected to +V with an inverter the output is high(1) with the input been low, and the output is low (0) when the input is high (1) And as for your resistor values, well the one for your base can be anything low i suppose, try 10K, 100K ? And for the collector, it just has to suit your emitter load i think, so in your case a LED.

23rd December 2007, 10:39 PM	(permalink)
Roff	Jaxx14, are you aware that you don't need an XOR, or any other logic gate, to do what you are apparently trying to do? It just makes things more difficult. That is, unless you plan to apply some other signal besides VCC to the other input of the XOR. What exactly are you trying to do? __________________ Ron (aka Rube)

24th December 2007, 12:55 PM	(permalink)
jaxx14	That PD? ,the photodiode is upside down yeah, cause i forgot to switch it. oh and that LEd i have there on the base, i am actually thinking of leaving that out. oh and the capacitor values may be 800microFarads and 300V. If that makes any difference. Oh and Roff i am trying to do an atomatic switch to my coilgun, before the second coil.

24th December 2007, 02:30 PM	(permalink)
Brian Hoskins	I would tackle your problem in a different way. Why not use the photodiode in series with a resistor and connected across the 5V power supply? Then, connect the junction of the photodiode and resistor to an Op-Amp setup as a comparator. This would be a much better circuit, and adjusting the point at which the comparator "trips" would be a simple matter of adjusting the reference voltage (use a variable pot). Calculating the value of the series resistor is also a simple matter, but you'd need to take a look at the datasheet for the photodiode first (to see how much current it passes for different light intensities). If you'd like me to draw up a circuit for this and explain it to you, I will. Please let me know what photodiode you are using. Brian

24th December 2007, 10:03 PM	(permalink)
jaxx14	Why am i using tha XOR gate? Because i have one lieing around. Oh and that photodiode is pretty old, it's a russian photodiode: fd-23k 11-78(these last numbers should be the production month and year). I have a lot of russian electronic parts. That thyristor is T122-25-12-4 the T122 is the type, 25 means 25A (continues) and 12 means 1200V, what does that 4 mean? i have no clue.

24th December 2007, 10:07 PM	(permalink)
Brian Hoskins	I can't find datasheets for any of those components. If datasheetcatalog.com doesn't have them, they probably don't exist! Brian

25th December 2007, 11:46 AM	(permalink)
jaxx14	I've allready searched them on the net and i think there aren't any datasheets for them. But those parts a pretty old, that photodiode has been made in 1978. and the T122 thyristor or SCR(should be the same thing) is also pretty old. BTW i've never found any datasheet for Russian type parts. For example take GT402I its a transistor with a pretty big capsule. i would take a picture of it but can't find my cam. Oh and for that Thyristor i found the numbers on the web, but thats was all, nothing more, only that it stands 25 A of current contiues and 1200V and thats all.

26th December 2007, 01:59 PM	(permalink)
jaxx14	Sry for the double post again, but soon i will be going to remake my schematic to a more reasonable schematic. Yesterday after going to sleep there was a flash in my head and i know how to draw what i need (i hope). I am not very good at drawing schematics from scratch, so this is pretty much my first time.

27th December 2007, 02:20 PM	(permalink)
Dean Huster	Since the general subject is XOR gates, I might add the point that if you try to "widen" the number of inputs by cascading 2-input gates (XORs are generally available only in 2-input versions) as you would AND or OR gates, the exclusivity disappears. An exclusive OR gate will have the logic of "if one and only one input is HIGH, the output will be HIGH; in all other cases, the output will be LOW". Cascaded XOR gates will have the logic of "if an odd number of inputs are HIGH, the output will be HIGH; in all other cases (an even number of inputs HIGH including no inputs HIGH) the output will be LOW". Regardless of the lack of exclusivity, the latter logic is great for creating a parity generator or parity checker. Dean __________________ Dean Huster, Electronics Curmudgeon Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines). R.I.P.