# AND gates

Discussion in 'General Electronics Chat' started by magnet18, Jun 5, 2011.

1. ### magnet18 Thread Starter Senior Member

Dec 22, 2010
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Hey, is there a 40xx series AND gate IC?
I would really like some, but can't seem to find any.

If there isn't, does anyone have any favorite and gate chips?
And could an op-amp be wired as an and gate?

2. ### #12 Expert

Nov 30, 2010
16,704
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3. ### #12 Expert

Nov 30, 2010
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I'm sure there are ways to do an op-amp as an and gate. For instance, set the (-) input at half of Vcc and use resistors so that it takes 2 high signals to insert enough current to get more than 1/2 Vcc volts across a resistor to ground, give that to the (+) input, no feedback on the amp, and the amp will flop like a comparator.

Reverse the terminals and it's a NAND.

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4. ### magnet18 Thread Starter Senior Member

Dec 22, 2010
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Ah, thanks, I wonder why I couldn't find those before :/

5. ### Ron H AAC Fanatic!

Apr 14, 2005
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CD 4081 is a quad 2 input AND. CD4073 is a triple 3 input AND. CD4082 is a dual 4 input AND. CD4068 is an 8 input gate with AND and NAND outputs.
You can make an AND gate by following a NAND with an inverter. You can make an inverter with a NAND gate by tying both inputs together, or by tying one input to VCC.
If you are having trouble understanding the RESET circuit I posted for your Nixie clock, come back here with questions and I will try to help you understand it.

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6. ### Ron H AAC Fanatic!

Apr 14, 2005
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You need to set the threshold at the -input to 3*Vcc/4, because with one input high and one input low, the +input will be at Vcc/2.
That's a really poor (and slow) way to make an AND gate. I suppose, if you have an op amp left over, and you don't mind that it takes as much as tens of microseconds or so to switch (depending on the op amp), then it only costs 4 resistors. A couple of diodes and a resistor would be better, except the op amp also acts as a buffer.

Last edited: Jun 5, 2011
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7. ### magnet18 Thread Starter Senior Member

Dec 22, 2010
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No, I got the reset circuit down after drawing some stuff on actual paper, it makes sense now.

I was wanting some for an alarm circuit, the dual 4 input should work great.
I also just wanted some so I have them available to use in stuff. As you said, transistor logic sucks quite badly.

Thanks for the info on the op-amps.

8. ### Ron H AAC Fanatic!

Apr 14, 2005
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NAND and NOR gates are the most versatile. In fact, you can implement any logic function using only NAND gates. Having said that, if you have the budget, an assortment is always nice to have on hand. Flip-flops, counters, etc., are also good to have in your stock of goodies.

Last edited: Jun 5, 2011
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9. ### magnet18 Thread Starter Senior Member

Dec 22, 2010
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Very useful site there, thanks.
So true, I'm beginning to develop a bit of a soft spot for the 4013

10. ### BillB3857 Senior Member

Feb 28, 2009
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I can remember back in the mid '70's that General Electric marketed a new Numerical Control called the Mark Century. Literally hundreds of transistor/diode/resistor 2 input NOR gates wired in various configurations. The control used negative logic where a low level was true and high was false. Like Ron H said, they are very flexible devices.

11. ### magnet18 Thread Starter Senior Member

Dec 22, 2010
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So the procedure for making a simple inverter is the same for both a NOR gate and a NAND gate?
Just tie the inputs together?

[EDIT]
Nevermind, looked at the tables again and answered that myself

Last edited: Jun 13, 2011
12. ### RRITESH KAKKAR Senior Member

Jun 29, 2010
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13. ### magnet18 Thread Starter Senior Member

Dec 22, 2010
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Thanks, I just got some in the mail actually

Good job on the display, looks great!

14. ### Ron H AAC Fanatic!

Apr 14, 2005
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Yes. Look at the truth tables:
Code ( (Unknown Language)):
1.
2. [B]NAND[/B]
3. A B Out
4. 0 0  1
5. 0 1  1
6. 1 0  1
7. 1 1  0
8. *****
9. [B]NOR[/B]
10. A B Out
11. 0 0  1
12. 0 1  0
13. 1 0  0
14. 1 1  0
15.
Note that, in NAND and in NOR, if both inputs are the same, the output is the complement of the inputs. That's an inverter.

You can also tie one NAND input high, and the output will be the complement of the other input. You can tie one NOR input low, and the output will be the complement of the other input.

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Dec 22, 2010
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16. ### SgtWookie Expert

Jul 17, 2007
22,183
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The 4093 quad NAND Schmitt trigger is a very useful IC; it can be used for quite a few things - besides being able to be wired as any other logic gate, you can also use it as an oscillator; gated or free-running. I suggest it's more useful than the 4011 NAND, as making an oscillator with the latter requires more parts and at least two gates instead of just one; and the Schmitt trigger allows the squaring-up of slow-rising waveforms.

You can make a square wave generator using just one 4093 NAND gate, one resistor wired from output to both inputs, and one capacitor from the input to ground; thus you can have up to four independent square wave generators per 4093 IC.

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17. ### #12 Expert

Nov 30, 2010
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Confirming...

a few decades ago I disassembled a portable TNS machine (Transcutaneous Nerve Stimulator) and it was all done with a hex-Schmidt and 4 or 5 transistors. Those Schimdt things are exceptionally versatile.

18. ### magnet18 Thread Starter Senior Member

Dec 22, 2010
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I always find it interesting, and slightly unnerving, how low-tech medical tools can be.
I watched a video of hip replacement surgery once (not by choice) and they basically used spherical cheese graters attached to your run-of-the-mill battery powered drill, accompanied by cutting out old bone with an angle grinder and setting the implant using a rubber mallet.

19. ### #12 Expert

Nov 30, 2010
16,704
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Once upon a time, I woke up and saw a doctor drilling a quarter inch hole in my tibia with a Black&Decker drill. Being rather incompetent at the moment, I tried to take the drill away from him!

Orthopedic surgeons often refer to themselves as "mechanics". Judging from the tools they use (and the results they get), I'd say it's not far off from the proper description.

20. ### shamsgul New Member

May 28, 2011
1
1
AND gate IC another name 7408

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