Alt-BEAM Archive

Message #12409



To: beam@sgiblab.sgi.com
From: Ben Hitchcock beh01@uow.edu.au
Date: Fri, 24 Mar 2000 12:38:30 +1100 (EST)
Subject: [alt-beam] Re: Logic puzzle - I need to built a new gate... :-)


My initial thoughts on this were: Wilf beat me to the best solution again.
So I plodded through all the possible states, and I think that maybe
Wilf's circuit might need some modifications...

Let's consider the case of both switches closed. Justin said that when
both switches were closed, he wanted output 1 to be high.

So to Wilf's diagram:
Switch 1 will allow current through to the 3904, turning it 'on'.
Switch 2 will ground the emitter, which because the transistor is on will
drag the output 1 down to ground.

This results in a closed,closed = low output, which I think should be
closed,closed = high.

In my circuit I neglected to mention that both switches should be
connected to Vcc.. details details.

Have I out-designed the almighty Wilf? :-) *hoping but not believing*

Ben

> Three components are needed as shown below:
>
> enjoy
>
> wilf
>
> <>
> > -----Original Message-----
> > From: Justin [SMTP:JAF60@student.canterbury.ac.nz]
> > Sent: Thursday, March 23, 2000 2:04 PM
> > To: beam@corp.sgi.com
> > Subject: Logic puzzle - I need to built a new gate... :-)
> >
> > 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 :-).
> >
> > The problem: (As illustrated below) I have a 4-state truth table and
> > want to build a circuit to give these outputs at the appropriate input.
> > It's easy if I use an XOR gate, but that would mean adding an entire
> > extra IC and I'll be trying to build small. My current solution when
> > freeformed would be slightly smaller than a chip, trouble is, it needs
> > adjusting when the voltage changes, and the voltage will change a lot
> > (solar walker) thus ruling out my design. I have no idea what the
> > circuit for an XOR gate is, and I think that could give someone who does
> > a big advantage.
> > The outputs are connected to the enable pins of a HC240, so that's the
> > kind of HIGH/LOW requirements the outputs have to meet.
> >
> > If someone could see a way to fix the sensitivity of my circuit, that
> > would also be great :-)
> >
> > Here is the guff: << File: puzzle1.gif >>

[Attachment, skipping...]


--
Nothing is foolproof to a sufficiently talented fool.



12410 Thu, 23 Mar 2000 18:25:44 -0700 [alt-beam] re: Beam Motors beam@sgiblab.sgi.com Robert Stein At 11:23 PM 3/23/00 +0000, you wrote:
>Curiously, Timothy, I saw a tutorial on the web somewhere for building a
>walker
>using a system like what you're describing. Cotton thread was used as a
>drive
>belt and little pulley wheels were placed on the motor shafts. Sorry, I
>didn't
>keep the URL. Frankly (no offence to whoever made the thing) it just didn't
>look like something I was likely to ever want to try doing myself. I
>couldn't
>imagine it working even half as well as the most rudimentary gearbox.
>
>Dennison, Timothy is right about the availability of gear motors I'm afraid.
>We aren't REALLY an industrialised society here (we just pretend). We export
>primary products like wheat, wool, coal etc. and import manufactured goods
>from
>Asia. Robot Oz doesn't seem to carry gearmotors and neither does anybody
>else,
>although I'm sure you could get them by breaking open camcorders etc. There
>probably is somewhere here that imports/makes gearmotors but they don't make
>them available to the general public. With a population of 18 million there
>just aren't that many people that want to buy half a dozen gear motors, so
>nobody that has them sells them in small quantities.
>
>Timothy, you have a couple of options. You could use servos. The cheapest
>I've seen run at about A$25. Any model shop should have them, especially if
>they sell remote control cars or planes. You can also order them from
>RobotOZ
>or Oatley electronics. I think beam online has a tutorial on how to modify
>them (you can't use them unmodified). There are many walkers made with
>servos
>and they seem to work well.
>
>Failing that, you could build your own gearbox or hack one from something
>else. I just bought a kitchen timer from woolworths that has a very
>promising
>gearbox inside it. The brand is "Propert" (an Australian tradition - you can
>tell because it says so on the packet, just near where it says "made in
>China")
>and its a 60 minute timer - looks like a white box with a dial on the front
>that goes from zero to 60. You find them in the kitchen section and they
>cost
>about A$5.50. A screwdriver is all you need to take the gearbox out and
>modify
>it by removing some of the unneeded parts. The only thing I have to
>figure out
>now is how to get the motor to mesh with the first gear. That shouldn't
>be too
>hard, I have a few ideas.
-snip-
Not to blow my own horn or anything, but there is a tutorial for converting
the timers to a gearbox. Although it uses parts obtained in the US. It
might give you ideas. It is at
www.dakotacom.net/~rastein/KTU_Walkman.htm. Hope it helps

Robert

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