Alt-BEAM Archive
Message #12232
To: beam@sgiblab.sgi.com
From: Dennison Bertram dibst11+@pitt.edu
Date: Mon, 20 Mar 2000 16:48:12 -0800
Subject: RE: SnakeBot Parts PACK
>
>
> P.S. Where DID you get those motors?
>
> Oooh! My special secret sauce. I collect them. They aren't very hard to
> find, and if you have some patience you can pick up quite a few. I've
gotten
> about twenty just pokeing around for them. Much like the motor zoom lens
> motors, just find a product that has the motors you want, and then search
> for them relentleslly. Persistance!
>
>
> dennison
>
>
12233 Mon, 20 Mar 2000 16:52:08 -0800 [alt-beam] Re: The 240 microcore - with corrected drawings - was ....yet ag "'beam@sgiblab.sgi.com'" Wilf Rigter
Here is a tested 74HC240 microcore (no, it's not a bicore) circuit first
posted and discussed 2/1/00 including the corrected drawings and a few more
comments.
It 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.
HOW TO READ THE DRAWINGS
For those not familiar with my schematic drawings, I use arrows on pins 1,
10, 19 and on one side of resistors R1 indicating connections to a common
ground bus to the 0V (or - terminal) of the powersupply. The +V connected on
pin 20 is the positive terminal of the powersupply. Not shown on the
drawings are the powersupply/battery itself and any supply filter components
which typically include a 0.1uF capacitor across pin 10 and pin 20 of the
240 chip. The layout drawing tries to show the physical arrangement of
external components with relation to the chip pins as well as the inverter
sections inside the chip. The inverters marked 1 are normally controlled
with pin 1G (1) and inverters marked 2 are controlled by pin 2G (19). In
this application pins 1G and 2G are connected to 0V making all inverters
active all the time. The C1 caps, apparently shown inside the 240 chip, are
actually external components mounted between the IC pins.
HOW IT WORKS
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 (+V supply) on the positive edge of the input signal. 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. I am
still trying to add a reverser function with minimal extra components and I
have some ideas which should work and which post shortly after I test them.
enjoy
wilf
<<240UCOR1.gif>> <<240UCORE.gif>>
> -----Original Message-----
> From: Scolman,Jim [SMTP:ScolmaJi@amsworld.com]
> Sent: Monday, March 20, 2000 3:30 PM
> To: BEAM Mailing List (E-mail)
> Subject: ....yet again.....
>
> Please forgive my density, but I feel I must keep asking this question
> until
> I understand the answer. Thanks to all of you that have trie to answer my
> past questions......but yet again....in the enclosed diagram, one of the
> power leads goes to the
> (+ plus) sign, where does the other go?........where is the (- neg)
> symbol?
> Is this a Bicore, MicroCore, or UniCore? All the "stuff" inside the
> outline
> of the chip.......is that internal to the chip or are those parts and
> connections to be fabricated and soldered? I still don't understand about
> ground.......where do you connect the 1G and 2G pins? The R1 resitors
> that
> just end in an arrow head......where do they connect? I am electronically
> challenged, but want to learn and build one of these things.....I have
> studied the FAQs and looked at the tutorials.....really. Thanks for your
> help......JWS. <<240UCORA.gif>>
>
>
Attachment: 240UCOR1.gif
Attachment: 240UCORE.gif
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