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Thread: Servo control questions
www.piclist.com/techref/io/servo/index.htm?key=servo
face picon face BY : email (remove spam text)(Olin Lathrop)



Apptech wrote:
> In the technology of the day, a (TTL) 74121 monostable and
> perhaps a 7474 or 7476 as a latch would allow a 2 IC
> solution, with a bit of head scratching to deal with dead
> time.
>
> Aaaagh !!!
>
>         http://focus.ti.com/lit/ds/symlink/sn74121.pdf

Nah, that one's for you upstarts after TI wussed out and went with those
annoying European standard logic symbols.  Back in 1976 they drew it right:
http://www.embedinc.com/temp/121.gif.

I haven't used 74 series logic chips in a long time for performing logic.
Yesterday I needed to convert a 3.3V digital signal to a 5V digital signal
in a one off circuit, and one of the old 74 series logic chips with their
TTL input thresholds came to mind.  That's when I realized the labels on
those drawers were so old that most of them had dried out and fallen off.  I
was just going thru the inventory and making up new labels when I read your
message.  I also discovered I have about 20 74121 in stock.  Not 74LS121 or
74HC121, just 74121.  I'm pretty sure the last time I bought any of those
was in college in the last 1970s when the TI TTL Data Book was essential
equipment for every EE.  http://www.embedinc.com/temp/ttl.jpg.


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