Alt-BEAM Archive

Message #12415



To: beam@sgiblab.sgi.com
From: Richard Weait crs0274@inforamp.net
Date: Thu, 23 Mar 2000 21:56:36 -0500
Subject: [alt-beam] Re: Logic puzzle - I need to built a new gate... :-)


At 10:03 AM 3/24/00 +1200, Justin wrote:
>Hiya,
>For the turning system of a walker I'm designing, I ran into an engaging
>logic problem that I thought I'd share will you (mainly in the hope that
>someone could solve it in a more elegant manner than I have :-).

Then Richard messed up his 'truth table.'


A B | O1 O2
----|------
0 0 | 1 X
1 0 | 1 0
1 1 | 0 0
0 1 | 1 X

Which should be like this when simplified:

A B | O1
----|---
0 0 | 1
1 0 | 1
1 1 | 1
0 1 | 0

So, I'll stick with my initial pull-up resistor to Vcc: 1M
Then I'll add SW-B to a gentle pull-down to ground: 100K
And SW-A to a strong pull-up to Vcc: 10K

Vcc o---/\/\/\---------.
1M |
--- |
Vcc o---/\/\/\---o o---o-----o /E
10K SW-A |
--- |
Gnd o---/\/\/\---o o---'
100K SW-B

So our output voltage to /E (the xx240 enable) is:

A B | /E
----|---
0 0 | 1 1M to Vcc
1 0 | 1 10K to Vcc
1 1 | 1 90% of Vcc (with 100K to ground not effective)
0 1 | 0 10% of Vcc (ground, with 1M to Vcc not effective)

Okay, so it isn't the most elegant. . . I just hope my first
post with the bad truth table disappears into the ether. :-)
Three passive components, two leads each. :-)

Cheers,

Richard.



Home