Alt-BEAM Archive
Message #11991
To: beam@sgiblab.sgi.com
From: Aaron Letts beamlist@yahoo.ca
Date: Thu, 16 Mar 2000 19:51:49 -0500 (EST)
Subject: [alt-beam] solder
How long should a soldering iron tip last? And what
can I do to make it last longer?
Aaron
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11992 Thu, 16 Mar 2000 20:06:24 -0500 [alt-beam] schematics (was ....microcore question....) beam@sgiblab.sgi.com Richard Weait At 05:53 PM 3/16/00 -0600, you wrote:
>Hi, yes,sorry, I still learning to use my scanner......I'm new to
>electronics to electronics too, so ok, one power lead goes to the plus,
>where does the other go, to one of the pins marked like this -----
>
>---
>
>-
[snip]
Hi Jim,
Okay, ground. It's a wire that doesn't get drawn. . . :-(
This is a very common point for confusion, so don't sweat it.
You can draw the ground connection just like any other wire.
Usually, ground is used in many places (in the schematic) so
the drawing can be made neater by using the symbol only, and
not drawing the wire from point to point to point.
Some circuits need some different grounds. :-( You could
see separate digital, analog, chassis, and earth grounds.
There are even be other designations that you might see, like
"cold water ground." Here are some of the different symbols
you'll see:
| | | |
----- ----- \ / ---
--- / / / V
-
In a system with balanced supplies (like +15V, -15V, and Gnd)
the third and fourth symbols above are usually the -V supply.
If you see more than one ground symbol in a schematic, look for
where it is defined.
The positive power supply can be as confusing. Digital chips
are sometimes drawn, and used without power pins; they are left
as assumed. . .
[dream sequence]
I worked at a place that had just received a new batch of PCBs.
None of them worked, because the power and ground pins had not been
connected on ANY of the digital IC's. They weren't drawn in the
schematics. The circuit design software would have caught the
error, but the chip libraries didn't have the power pins either. . .
[wake up, screaming, end dream sequence]
Power supply pins can be drawn without the connecting wires, too.
^ --- O
/ \ | |
| | |
Again, drawings can be neater without all those nasty lines
all over the place. Maybe that's just one way to impress the
beginners? Let them breadboard a circuit and impress them when
you make it work by connecting two wires. . . power and ground.
What is ground?
That is a common question. The answer is: it depends. In
most of the BEAM circuits on this list, ground is assumed to
be the common connection for the 0 volt power supply. Your
five volt power supply has two wires; the five volt wire, and
the zero volt wire (or ground.) It is the reference point to
which all voltage measurements are made unless explicitly stated
otherwise. So if someone says, "When the capacitor charges
to 2.4V the circuit will trigger" you will know that the
voltage across the capacitor will be measured with respect to
ground. Ground is where you put the black ground lead of
your multi-meter.
A couple of quick points about drawing ASCII-schematics like
the ones I put in this email:
a) keep the width of the text line low, like under 70 characters.
b) use a mono-spaced font to type it (and to view others')
c) end a line with the enter / return key
d) always use the space bar and never the 'tab' key
Deviating from these guidelines limits the number of people
that will be able to read your schematics.
Good luck!
Richard.
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