Alt-BEAM Archive

Message #09732



To: 'beam@sgiblab.sgi.com'
From: owner-beam@sgiblab.sgi.com [mailto:owner-beam@sgiblab.sgi.com]On
Date: Wed, 2 Feb 2000 22:43:06 -0800
Subject: The 240 microcore - was RE: Bicore question



And they said it couldn't be done!

Here is a tested 74HC240 microcore (no not a bicore) circuit which behaves
just like a 74HC14 type microcore and motor driver combined. I have bench
tested the circuit with small lens motors and VCR ejector motors. Stalling
the motors by hand produces a slightly shorter pulse duration but otherwise
the circuit just keeps on ticking. The motion of the motors is the
characteristic non-overlapping microcore sequence. The circuit is similar
to the "quasi microcore" design I reported some time ago.

The new 240 uCore circuit is similar to a microcore but uses normal HC240
inverters instead of Schmitt triggers. Such a linear microcore circuit
normally would not work but this problem is overcome by adding positive
feedback from the non-inverted motor driver outputs using a capacitor. This
positive feedback speeds up the transition through the linear region using
what I call AC hysteresis. Assuming a switching threshold of 1/2Vdd, the
ratio of C1/C2 must be greater than 2 and the time constant will be
proportional to R*(C1+C2) since the bias point input voltage will clamp at
Vdd on the positive edge of the input signal. Note the location of the C1
caps, some of which are mounted between pins on the solder side of the chip.
The two diodes (which can be any type 1N914/1N4448 etc) provide an automatic
PNC function, far simpler and easier to use than the old Nu type PNC
circuit. The layout of this circuit would appear to lend itself very well to
freeforming. If possible, I will try to incorporate a reverser function to
this circuit without adding (many) more parts unless someone beats me to it
of course.

enjoy

wilf
<<240UCOR1.gif>> <<240UCORE.gif>>
> -----Original Message-----
> From: Phillip A. Ryals [SMTP:phillip@ryals.com]
> Sent: Sunday, January 30, 2000 9:21 AM
> To: beam@sgiblab.sgi.com
> Subject: Re: Bicore question
>
> > Ok I'm feed up with trying to make a Microcore walker.
> > Ao I've turned to the bicore.
>
> Thanks what I'm screaming! I've made two m/s bicore walkers, and decided
> to
> go to the microcore. I thought it would act more along the lines of what
> I
> wanted it to do.
>
> I breadboard it, and it works fine. I solder it all together, and it
> refuses to work. I've checked all my solder joints, and made sure
> everything's touching where it should, but I still can't manage a working
> model. All I'm left with now, is perhaps that I ruined the chip with
> heat.
> Are the 14's more sensitive than the 240's? I'm using one of those
> universal PCB's, and I soldered all the pins of the 14 at once. Is that a
> problem? I haven't had a problem doing it that way with 240's and 245's,
> so
> I figured I could get away with it.
>
> Any suggestions?
>
> -phillip

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