Orchid XP v8 wrote:
> Tom Austin wrote:
>> Nicolas Alvarez wrote:
>>> Tom Austin <taustin> wrote:
>>>> One think to keep in mind, you are best off not trying to drive the LED
>>>> directly from the chip.  Some chips can do it, but most cannot.  
>>>> Lots of
>>>> times you need to put a *switch* that the gate switches.
>>>
>>> I have an electronics kit, with CMOS ICs, LEDs, and AA batteries 
>>> adding up
>>> to 9v. I have always connected LEDs directly at the output of gates. 
>>> With a
>>> resistor, of course (3.3k ohm), I mean without any kind of switch.
>>>
>>
>>
>> With TTL you should be able to drive a LED from the outputs.
>> With CMOS you better check to be sure.
> 
> I have an electronics kit with TTL in it. (A 7400LS, no less.) All the 
> diagrams drive the LEDs directly from it.
> 

That's TTL - it can source current, i.e. drive a LED
CMOS usually cannot source as much current.

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