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[DPRG] current conversion [and much more]

Subject: [DPRG] current conversion [and much more]
From: David Peterson robologist at yahoo.com
Date: Tue Jul 24 15:29:02 CDT 2001

I'm guessing your first requirement of an input of 6 to 26 v is for the
Super Tcomps own low drop out regulator, from which you are supplying the 5v
that components b, c, and d need. A regular 9 v battery doesn't supply
enough current on it's own to run everything that you have together, hence
you see the LCD quit working when your servos kick in. You might consider a
4 or more AA pack, only nominally 6 v, but with more current capability than
a single 9 v. Or you could parallel another 9 v with the one you already
have. Or you could use a rechargable 7.2 or 9.6 v NiCad pack with more than
enough current to feed everything. I have a small minisumo that would
constantly reset when running with just 1 9 volt, so 2 paralleled was just
enough for it. You may need more considering the LCD and 4 servos, both of
which reqiure a bit of current. Perhaps even the rechargable batteries in
the same size as your 9 v will actually supply enough current, though most
of these are actually 7.2 v , some are 8.4 v. These are the NiCad or NiMh
rechargables I'm refering to that probably deliver more current than the
normal alkaline batteries. Be sure to watch the temperature on the
regulator of the Super T-comp, possibly an LM2940 that might need a heat
sink to supply everything. Hope this helps.
David P
----- Original Message -----
>From: "montgomery f. tidwell" <mtidwell at practicalmatters.com>
To: "DPRGlist" <DPRGlist at dprg.org>
Sent: Tuesday, July 24, 2001 11:54 AM
Subject: Re: [DPRG] current conversion [and much more]

> Howdy,
> maybe i'm trying to dictate an answer when i don't fully understand the
> problem.
> i've created a line-follower that has (a) Super TComp, (b) LCD Serial
> Backpack, (c) 4 HS303 servos, (d) custom line sensor with 3 LED/CDS
> pairs. (a) was powered by a 9V, and everything else came from a 5V
> line off (a).
> the input requirements are: (a) 6-26V, (b) 4.8-5.5V, (c)4.8-6V,
> (d) 5V (much higher and the LEDs burn out).
> i have found that if more than one servo is active, the LCD goes
> blank. i assume that the servos are taking too much power for the
> LCD to operate.
> so i thought that it might be better to have one 9V for (a), and
> one something else (regulated to 5V) for everything else. i don't
> really want a different battery for every part.
> whew. now what do you suggest?
>                                   \\//_
> Mike McCarty wrote:
> > On Tue, 24 Jul 2001, montgomery f. tidwell wrote:
> >
> >
> >>Howdy,
> >>
> >>almost, the source would be from about 5V to 18V (or so).
> >>
> >>7.5V might be a bit too high (for a minimum input).
> >>
> >
> >
> > The circuit itself has to have some "headroom" to operate. There are
> > low dropout regulators available. How much current do you need? How
> > tight regulation? If you don't need too tight regulation or too much
> > current, then just a Zener diode might do.
> >
> > Mike
> >
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