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From: wiml@blake.acs.washington.edu (William Lewis)
Newsgroups: sci.electronics
Subject: Re: Circut needed
Keywords: inexpensive
Message-ID: <6320@blake.acs.washington.edu>
Date: 21 Mar 90 05:00:40 GMT
References: <1990Mar19.154615.22362@tree.uucp> <1342@carroll1.cc.edu>
Reply-To: wiml@blake.acs.washington.edu (William Lewis)
Organization: University of Washington, Seattle
Lines: 46

In article <1990Mar19.154615.22362@tree.uucp> mirandor@.PacBell.COM (W. Le Roy Davis (1-23-90)) writes:
>I am looking for the circut for a very inexpensive three event detector.
>I work with the Boy Scouts, and they have this "pine box derby" involving small
>(8" long) cars on tracks.  They run three at a time.  I need an easy to main-
>tain circut that detects the cars crossing the finish line and determines 1st,
>2nd, and 3rd place.  I would like to keep the circutry down to 74xx type chips.
>I have had several friends suggest timed circuts, but that is getting too
>complex.

In article <1342@carroll1.cc.edu> tkopp@carroll1.cc.edu (Tom Kopp) writes:
>Well, Just thinking for a few minutes, I have a circuit that you can use

   Hmm, ditto. Gate / chip count follows, assuming you want to use 74xx
chips:

   Per car, 8 NANDs;
   Plus, two three-input NORs (or a pair of ORs and an inverter;
I don't think there's a dual-3-inp-NOR chip in the 74xx family?)
for arbitration.

   Chip count would be a total of six 7400s, a 7404, and a 7432, 
ending up with four spare inverters (input buffering? output drivers?).
This includes no real-world interfacing; you'd need (as Mr. Kopp
notes) three switches for the cars and a momentary to clear the
circuit. The output is in the form of a pair of lights per car: two lit
for first place, one for second, none for third. Three more chips
(ANDs, XORs, NORs) gets you a 1-of-3 display for each car. (And
three more wasted gates on those four-gate chips :-( ) And of course,
you'll need to add drivers on those outputs (switching transistors,
SCRs, elves with little flags, whatever ... 
  And to use someone else's words in conclusion (ain't F>ollowups
great? :-) ), 
>If you think this sounds simple enough, let me know and I'll come up
>with a schematic for it - at least one that can be breadboarded - I hate
>trying to come up with PCboard schematics, so that's up to you if you
>want to do it!
>-- 
>Thomas J. Kopp - Carroll College, Waukesha, WI
>	tkopp@carroll1.cc.edu 	 uunet!marque!carroll1!tkopp
>"Some people aim to live the longest.  My goal is to live the most." - Me

   Well, I think I'll use my own .signature ...


-- 
wiml@blake.acs.washington.edu        (206)526-5885      Seattle, Washington