From: "Walter Harley"
Subject: Re: Need schematic for digital timer (Help)
Date: Wed, 30 Oct 2002 18:57:14 -0800
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Reply-To: "Walter Harley"
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"Justin Time" wrote in message
> Our textbook only discusses the use of gates / 555 timers / D
> flip-flops in terms of generalities and offers no specific design
> information. There isn't time to order a book.
The library is often a good resource in such a situation, and teaching
assistants sometimes are as well.
The basic idea is that you make an oscillator (perhaps using a 555, though
there are other ways); you then drive a series of flip-flops with the
oscillator, resulting in a series of divisions by two, which can be viewed
collectively as a binary number; you then use gates to perform actions when
specific binary numbers occur.
Chips are available which combine some of these functions. For instance,
there are "counter" chips which include a series of flip-flop dividers, all
nicely hooked together for you.
Be aware that CMOS logic is generally much easier to work with than TTL.
Unless you're required to work with TTL, I would suggest using CMOS. (All
the 7400-series TTL devices are available as 74C00-series CMOS, but there is
also a 4000 series of CMOS with additional useful functions.)
You could also do the whole thing in software, using a microcontroller (like
a "BASIC Stamp"). I suspect your class may not yet be at that level,
though; and after, all you've got to learn somehow how that microcontroller