From: "Ken Taylor"
Subject: Re: circuit design help
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Sat, 19 Oct 2002 19:43:26 +1300
NNTP-Posting-Date: Sat, 19 Oct 2002 19:42:29 NZDT
"chris bergeron" wrote in message
> I'm not sure if this is the right place for this or not. If it's not,
> please let me know (I'm not a spammer!) and I will go elsewhere. I need
> help designing a circuit. I have a timing design (which is attached).
> I'm willing to pay nicely for help in desiging this circuit. It seems
> like a simple circuit; but as a novice hobbyist in electronics, I'm
> stumped at how to go about it. I've toiled with using a 555/556 and or
> a 7447 (or maybe it's a 7474). Anyway, I obviously don't have the skill
> to design this circuit. I know a decent [small?] amount about
> electronics (transistors, relays, ICs, etc); enough to attempt the
> circuit and fail. Hence my posting here.
> Attached is a [relatively] simple circuit that I'll pay decently for
> help desiging. I've tried, but failed; and as such, I know when to ask
> for help.
> Thanks to anyone that can provide assistance!
Look up the 74121, a monostable. http://www.national.com/pf/54/54121.html
Use it for the time delays. Use the positive going and negative going edges
of the input to generate the output B. Use the positive going edge of the
input to start another timer, the end of which sets a flip-flop ( eg.
http://www.national.com/pf/54/5474.html ) for output A. The negative edge of
the input resets this flip-flop. Another flip-flop (the second half of the
7474) is set by the positive going edge of the input; the negative going
edge of the input starts another timer, the end of which resets the last
flip-flop (output C).
Have I made that clear? Check the data sheets, treat things one at a time
and it'll all fall out pretty easily.