Alt-BEAM Archive
Message #06003
To: beam@sgiblab.sgi.com
From: Darrell Johnson beamtastic@yahoo.com
Date: Wed, 8 Sep 1999 21:21:16 -0700 (PDT)
Subject: [alt-beam] Re: PS HEAD V2
Wilf, is there a big difference in the performance between v1 and v2 of
the PSH? I was just curious, since I built the v1 PSH and it performs
very well for me..
I'm sure this will be of interest to others, so I'm posting it to the
list..
thanks..
Darrell
(I'm planning on breadboarding PSHv2 as soon as I get back home next
week...)
--- Wilf Rigter wrote:
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6004 Thu, 9 Sep 1999 01:39:59 EDT [alt-beam] Re: PS HEAD V2 beam@sgiblab.sgi.com Bumper314@aol.com In a message dated 9/8/99 9:24:07 PM Pacific Daylight Time,=20
beamtastic@yahoo.com writes:
> Wilf, is there a big difference in the performance between v1 and v2 of
> the PSH? I was just curious, since I built the v1 PSH and it performs
> very well for me..=20
> I'm sure this will be of interest to others, so I'm posting it to the
> list..
> thanks..
Well me and my bad luck were unable to breadboard this little circuit...very=20
very simple circuit...sigh..so im curious if it could be because i used .1=
=B5f=20
caps instead of .01?
steve
6005 Thu, 09 Sep 1999 18:11:49 +0000 [alt-beam] Re: ground? beam@corp.sgi.com "Ben Hitchcock" Hi,
>hello...i was wondering if anyone knows the difference between digital
>ground, auido ground, and ground? thanks
>
>steve
Ground is usually taken as being zero volts with respect to the rest of the
circuit. It's a convenient place to stick the black lead of your
multimeter. That being said, you probably already knew that, judging from
the wording of your question...
Ground isn't always as noise-free as you might hope for. For example, I
have done some (not a lot, but some) audio work, and for a decent amplifier,
you usually have a separate signal ground and a power ground.
So why the two grounds?
It all comes back to V = I * R. Say the ground wire you are using has a
resistance of half an ohm, between the point you are using as a zero
reference, and another point that leakage is occurring. Say that there is
20 mA flowing though it, due to that very same leakage.
So, as V = IR,
V = 0.02 * .5
= 0.01 Volts.
If the power supply is coming from the mains, this will result in your
'electrical ground' near the leak having a 0.01 volt ripple on it. If this
'electrical ground' is used as an 'audio ground' then you will hear a hum.
If you use different grounds, so you have an audio ground and an
'electrical' ground, then there will be a lot less current flowing in the
audio ground - so lots less voltage, and so lots less noise.
It's really just being pedantic where you have a high-fidelity device, and
you want as little interference as possible. One solution is to have a
'star point' ground, where all the grounds come together at one (and ONLY
one) point, and this point is considered ground. This solution means that
the different grounds can't interfere with each other.
Hope this helps!
Ben Hitchcock
6006 Thu, 09 Sep 1999 14:47:39 -0400 [alt-beam] motor driver: h-bridge or IC? beam@sgiblab.sgi.com SG Hi all,
I think one of my 6 transistor h-bridges burned
out (i hope thats what the problem is anyway)
and rather than solder some more transitors together, i thought i might try
two 74HCT245's stacked.
Does anyone know if this will be enough to power standard servo's?
Thanks!
-Sparky
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