Alt-BEAM Archive

Message #13781



To: beam@sgiblab.sgi.com
From: "Ben Hitchcock" beh01@uow.edu.au
Date: Fri, 21 Apr 2000 23:04:17 +1000
Subject: Re: The sensitivity of a 74XX240


Hi Jason,

One thing to try is putting a small light globe (like out of a torch) in
series with the battery when you're building the circuit. If you connect
something up the wrong way, the globe will light up. With the sort of
motors we use, when the motors are firing away the globe might glow dimly
but not as brightly as if you connect a chip in backwards.

I learnt this trick when debugging TVs at an electronics repair section at
the steelworks where I work. Peter (the technician who was mentoring me)
would put a big car headlight in series with the 12V supply. When he made a
mistake, everyone knew about it! But the light will limit the current to a
reasonable level. When everything's working properly, the light is off.
It's like an "Error" light. It also saves your components from overcurrent.

The nice thing about this method is that when the filament is cold, the
resistance is a lot lower than when the filament is hot... so it's sort of
like a fuse in that regard. Experiment with a couple of different globes to
see which one works best for you.

I just tried it with a 2.4V 0.7A globe out of a torch (2 x D cell) and when
in series with my NSDummy walker walking away, I couldn't even see the
filament glow. I also tried it with a 74HC240 chip connected backwards, and
the light lit up very brightly. Maybe it might be an idea to try a higher
voltage globe - maybe if you can find one a 4.5 globe at about 0.3 A or so
would work well.

Since it doesn't weigh much, and doesn't suck any power normally you might
consider adding one permanently to future projects. I don't know about you,
but I'm always adding bits to my robots and this would save a lot of chips
that might otherwise end up toasted. Or you could just use one as your
debugging tool, taking it out of circuit when you know that everything's
working properly.

Ben


----------
>From: "Jason -"
>To: beam@sgiblab.sgi.com
>Subject: The sensitivity of a 74XX240
>Date: Fri, 21 Apr 2000 22:08
>

>
> Hie all,
>
> i have been very frustrated with all those broken chips i have ,
> the problem is they are very fragile esspecially the 74xx240...the is one
> time which i fried it just by connecting the wrong polarities of the chip to
> a 4V battery..........so i would like to know is there any special way for
> me to look after them.....and will direct soldering when i am free forming a
> circuit make it become bad too......thanks
>
> ________________________________________________________________________
> Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com



13782 Fri, 21 Apr 2000 08:11:23 -0700 Lift potential for motors? beam@sgiblab.sgi.com owner-beam@sgiblab.sgi.com [mailto:owner-beam@sgiblab.sgi.com]On
Again a silly question ... how do I more or less find out the lifting power
of a motor
when connected to an average efficiency propeller?
Ideally I'd like to know how cheap I can buy a motor that can lift a bit
more than
just itself, as my funds are quite limited at the moment :(

Thanks in advance,

X.

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