Alt-BEAM Archive
Message #09398
To: beam@sgiblab.sgi.com (mailing list)
From: Ben Hitchcock beh01@uow.edu.au
Date: Thu, 20 Jan 2000 14:19:19 +1100 (EST)
Subject: [alt-beam] Re: Grounding???
----- Forwarded message from Ian Bushong -----
I am beginning in electronics, and I am stuck on the concept of
grounding. Exactly what is its purpose and what do the connection
indications on schematics connect to? From what I can make of it, it
seems to be a part of a circuit with no electrical potential. Is this
right? How is that possible? Could you maybe explain it further.
Somewhere I read that the ground is sometimes connected to a metal
chassis. And why are there sometimes more than one of them and sometimes
none at all (like in smaller BEAM circuits). I have also noticed that
there are also sometimes resistors or caps in between the circuit and
ground (??). As you can see, I am VERY confused and would really
appreciate a simple explanation. I can't seem to find anything about it
anywhere.
-Ian Bushong
------------------------------------------------------------------------
Hi,
Ground is just a convenient place to attach things to. That's it.
As you would know, you need two wires to make current flow (through a
light or whatever). Rather
than actually use two wires, many devices use the frame of the object
itself as the return path for the electricity.
In a
car, for example, the negative (usually) terminal of the battery is
attached to the metal frame of the car. If you want the brake light to
go on, for example, you only need one wire to go to the light. The return
path for the electricity is the frame of the car itself.
In a BEAM schematic, things aren't quite as simple. You can make the
chassis of your robot equal to ground, or +V, or not connected at all!
But, when you look at the schematic, it doesn't matter. All that matters
is that all the grounds get connected together somehow. Whether this is
through a wire link (like in my FRED robot) or through the chassis of
the robot doesn't matter. So then 'ground' is really the point that you
decide shall be equal to ground, and want to attach the black lead of your
multimeter to. That's it.
I would suggest using the negative lead of your capacitor (if making a
solar powered device) as your ground. I did this in Alf. Just solder
every ground on the schematic to this lead, and everything should work
fine.
You might decide to solder this lead to the frame of the robot as well,
and then when you need a ground connection you can use the frame itself.
Think of the frame then as an extension of the negative terminal of the
cap.
As for it having no electric potential, that's right - in relation to
ground. Voltage is defined as the potential difference between two
points. The standard is to define one of the points as ground, then you
only have to worry about one lead on your multimeter, instead of two. So
another part of the circuit that is grounded will be connected to your
first ground, so there will be no voltage on it!
By the way, 'ground' in this post means "connected to the point that you
define to be ground", it has nothing to do with the stuff that plants grow
in. They are related - but that involves discussing three-phase power and
fault currents and trust me you really DON'T want to know about that just
yet!
Hope this hasn't confused you more than you were before!
Ben
9399 19 Jan 2000 19:20:24 -0800 [alt-beam] many questions beam@sgiblab.sgi.com iphotope@canada.com Hello again!
I have a few questions that have been
nagging at me for a while:
1. I noticed that on many circuits, there
is a +whatever input and a ground, but
no -whatever. Is the ground the
-whatever, or is this a cruel trick?
2. In the FLED solar engine, does the
blink rate of the FLED matter?
3. What would the specs for a perfect
BEAM robot motor be?
4. Has anyone ever implemented remote-
control into a BEAM walker robot?
Thank you for your help in advance,
Iphotope
P.S. that web page I promised is almost
done.
__________________________________________________________
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9400 Wed, 19 Jan 2000 19:40:10 -0800 [alt-beam] Re: Grounding??? beam@sgiblab.sgi.com Ian Bushong THANK YOU!!!! That really clarified it for me. I almost had the concept, but
your explanation connected it! Thnx again!
-Ian
Ben Hitchcock wrote:
> ----- Forwarded message from Ian Bushong -----
> I am beginning in electronics, and I am stuck on the concept of
> grounding. Exactly what is its purpose and what do the connection
> indications on schematics connect to? From what I can make of it, it
> seems to be a part of a circuit with no electrical potential. Is this
> right? How is that possible? Could you maybe explain it further.
> Somewhere I read that the ground is sometimes connected to a metal
> chassis. And why are there sometimes more than one of them and sometimes
> none at all (like in smaller BEAM circuits). I have also noticed that
> there are also sometimes resistors or caps in between the circuit and
> ground (??). As you can see, I am VERY confused and would really
> appreciate a simple explanation. I can't seem to find anything about it
> anywhere.
>
> -Ian Bushong
> ------------------------------------------------------------------------
> Hi,
>
> Ground is just a convenient place to attach things to. That's it.
>
> As you would know, you need two wires to make current flow (through a
> light or whatever). Rather
> than actually use two wires, many devices use the frame of the object
> itself as the return path for the electricity.
>
> In a
> car, for example, the negative (usually) terminal of the battery is
> attached to the metal frame of the car. If you want the brake light to
> go on, for example, you only need one wire to go to the light. The return
> path for the electricity is the frame of the car itself.
>
> In a BEAM schematic, things aren't quite as simple. You can make the
> chassis of your robot equal to ground, or +V, or not connected at all!
>
> But, when you look at the schematic, it doesn't matter. All that matters
> is that all the grounds get connected together somehow. Whether this is
> through a wire link (like in my FRED robot) or through the chassis of
> the robot doesn't matter. So then 'ground' is really the point that you
> decide shall be equal to ground, and want to attach the black lead of your
> multimeter to. That's it.
>
> I would suggest using the negative lead of your capacitor (if making a
> solar powered device) as your ground. I did this in Alf. Just solder
> every ground on the schematic to this lead, and everything should work
> fine.
>
> You might decide to solder this lead to the frame of the robot as well,
> and then when you need a ground connection you can use the frame itself.
> Think of the frame then as an extension of the negative terminal of the
> cap.
>
> As for it having no electric potential, that's right - in relation to
> ground. Voltage is defined as the potential difference between two
> points. The standard is to define one of the points as ground, then you
> only have to worry about one lead on your multimeter, instead of two. So
> another part of the circuit that is grounded will be connected to your
> first ground, so there will be no voltage on it!
>
> By the way, 'ground' in this post means "connected to the point that you
> define to be ground", it has nothing to do with the stuff that plants grow
> in. They are related - but that involves discussing three-phase power and
> fault currents and trust me you really DON'T want to know about that just
> yet!
>
> Hope this hasn't confused you more than you were before!
> Ben
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