A complete newbie question here: I've got some logic gates from Texas Instruments and would like to understand why the left circuit doesn't work while the right one works well (and.jpg) and why the NOT-gate doesn't work at all (not.jpg).
Here are the datasheets:
Show us a good image of your wiring.
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This is not a very good IC for driving an LED. Check the datasheet. Look for IOH. (it's -0.4mA). This is the recommended operating current that can be sourced. Note that IOL is 8mA, which is the recommended sink current.
You could use the LED so that it illuminates when the 74LS08 output is low. Sink current = (5-2)/470 = 6.4mA.
Connection: [74LS08 pin3] ●-------● [-LED+] ●-------● [470Ω] ●-------● [+5V]
I hope this quality is good enough.
I don't understand, why OUT (green cable) still "high" (and the LED on) even if both inputs (yellow cables) are off (here both are on).
dlloyd:
This is not a very good IC for driving an LED.
Could you please tell me which ICs are good enough for this?
I've got:
Don't see a GND wire going from pin 7 to the Arduino GND.
Note: Could use breadboard blue bus as a GND bus for convenience for multiple GND connections. Also, its good practice to tie all unused inputs on the logic ICs to Vcc or GND.
See my previous post for output driving currents and suggestion.
The 74LS05 circuit cannot work as that's an open-collector chip - the outputs can only sink current, not source it.
You are lacking decoupling caps on your chips BTW - don't get into that bad habit, 100nF ceramic for each chip is a good starting point. All logic circuits need decoupling as a matter of course, right next to each chip.
The 74LS08 circuit issue must be a wiring one.
The 74LS series is TTL, not CMOS, and can sink far more current than it can source, TTL loads are usually
to 5V, not to GND, as a consequence.
CMOS is symmetrical and you can drive loads either way.
You would fare better to use modern CMOS families like 74HC, so 74HC08 and gates, 74HC14 not gates (everyone uses the '14 because it has schmitt-trigger inputs which are very useful for signal conditioning).
The 74HC family will run from 2V to 6V supply too with extremely low power consumption, whereas TTL
families require exactly 5V and are power hungry.
Unconnected inputs are not good news for CMOS logic though, can cause oscillations and higher power consumption.
Could you please tell me which ICs are good enough for this?
Its the logic family that's the problem. Replace LS with HC in the part numbers to get higher and balanced source/sink currents. (hah, in terms of speed ... I'm the LS version, MarkT is HC or ACT)
dlloyd:
Don't see a GND wire going from pin 7 to the Arduino GND.
It's connected to the GND as well as LED.
All my GND cables are blue.
Well, I see it's not as easy, as I thought (a bit more specs which matter than I thought). Thank you.
So my question is, are there logic gates I could use to work with LEDs using Arduino just as a 5V- and GND-source?
I don't interested in speed.
I just need this ICs to demonstrate hardware logic gates working as expected.
So I just buy
Not the wire colour ... I meant you could make use of the breadboard bus marked with a blue line.
74HC08N, etc would work good with LEDs.
dlloyd:
breadboard bus marked with a blue line.
But I did! All GNDs are connected to the blue line on the top and the blue line itself is connected to Arduino's GND.
The reason why the NOT-gate doesn't work at all is probably the same - IC family?
Will I need some extra resistors or anything else for circuits?
Pay attention to unconnected input/control pins on HC chips.
Terminate to High or Low as needed.
Start creating good wiring habits.
Edit: here is a good example.
Yours
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Yes, apparently you did (next time I'll zoom out a bit more when looking at a picture).
The reason why the NOT-gate doesn't work at all is probably the same -- IC family?
Yes.
With the existing IC, you could connect the LED as shown in a previous reply so that it illuminates when the output goes low.
Buzz your buttons too, make sure you're actually using legs that are open when the button is not pressed.
Will I need some extra resistors or anything else for circuits?
Your 200Ω resistors are fine with the HC CMOS logic family. To test your existing LS ICs, could connect as mentioned earlier but use two 200Ω in series if you don't have 470Ω.
LarryD:
Terminate to High or Low as needed.[/img]
For my demo I need only two inputs (well obviously only one on NOT) and one output on each chip.
So I'll have to connect all other inputs to GND?
CrossRoads:
Buzz your buttons too
But I don't use any buttons.
Will you please double check my "shopping list" please?
I think Crossroads was looking at my example while I was still editing.
Yes, you need to connect inputs on all unused gate to either High or Low.
What are you trying to accomplish with all This?
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AND
NAND
OR
NOR
XOR
NOT
If these match your list you should be good to go.
Edit
Some of your gates have Schmitt-trigger inputs, is that what you wanted?
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LarryD:
What are you trying to accomplish with all This?
It should be a simple demo with "real" (hardware) logic gates. I will demonstrate for example that 1 XOR 1 equals 0 (LED off), or NOT 0 equals 1 (LED on), nothing more.
LarryD:
Some of your gates have Schmitt-trigger inputs, is that what you wanted?
MarkT said, "everyone uses the '14" so I thought I should use them too.
The "regular" NAND SN74HC38N is not available at my local store btw.
The regular NAND is 7400, the 7438 is a one-of-8 decoder.
There is nothing wrong with Schmitt-trigger inputs, just pointing this out to you.
In fact they might be more preferable in applications.
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