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Mauledriver(at)nc.rr.com
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 Posted: Thu Aug 30, 2012 9:45 am Post subject: "Pulled Low to Ground"........(Huh?) |
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Yes, "pull to ground" still doesn't sound right for this electronic
amateur but yes, that's what it means. It means the other wire of the
switch is connected to ground. Either one will work because they are
the same but... don't know.
Bill
On 8/30/2012 1:21 PM, stearman456 wrote:
| Quote: |
In the Garmin SL-40 installation guide it says that both the transmit and intercomm push-to-talks need to be "pulled low to ground". I'm asuming they just mean the other wire of the switch goes to ground? I'm also asuming they mean radio/contact ground, not airframe ground? Or am I missing something? Wish I could post the schematic but I'm working from my Ipad and haven't figured out how to do that yet!
Dan
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=382142#382142
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Mauledriver(at)nc.rr.com
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| Posted: Thu Aug 30, 2012 10:19 am Post subject: "Pulled Low to Ground"........(Huh?) |
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On 8/30/2012 1:44 PM, Bill Watson wrote:
| Quote: |
<Mauledriver(at)nc.rr.com>
Yes, "pull to ground" still doesn't sound right for this electronic
amateur but yes, that's what it means. It means the other wire of
the switch is connected to ground. Either one will work because they
are the "same" but there may be a distinction
|
that makes the radio ground optimal... but I don't really know.
The way I understand it, I have all my avionic grounds run to a single
point and all my "pull to grounds" therefore are grounded to the same point.
| Quote: |
Bill
On 8/30/2012 1:21 PM, stearman456 wrote:
>
> <warbirds(at)shaw.ca>
>
> In the Garmin SL-40 installation guide it says that both the transmit
> and intercomm push-to-talks need to be "pulled low to ground". I'm
> asuming they just mean the other wire of the switch goes to ground?
> I'm also asuming they mean radio/contact ground, not airframe
> ground? Or am I missing something? Wish I could post the schematic
> but I'm working from my Ipad and haven't figured out how to do that yet!
>
> Dan
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=382142#382142
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
-----
No virus found in this message.
Checked by AVG - www.avg.com
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nuckolls.bob(at)aeroelect
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| Posted: Thu Aug 30, 2012 11:45 am Post subject: "Pulled Low to Ground"........(Huh?) |
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At 12:21 PM 8/30/2012, you wrote:
| Quote: | --> AeroElectric-List message posted by: "stearman456" <warbirds(at)shaw.ca>
In the Garmin SL-40 installation guide it says that both the transmit and intercomm push-to-talks need to be "pulled low to ground". I'm asuming they just mean the other wire of the switch goes to ground? I'm also asuming they mean radio/contact ground, not airframe ground? Or am I missing something? Wish I could post the schematic but I'm working from my Ipad and haven't figured out how to do that yet! |
This is an unfortunate scrambling of vernacular.
The function of a discrete CONTROL or SIGNAL path
is often described using these terms. For example,
the legacy control philosophy for closing the battery
contactor may be described as "pull to ground", "active
low", "pulled down", "low side switched" or simply
"switched ground". All of these phrases will bring
the same image to mind for someone who works across
several disciplines in electronics.
The other side of the coin describes the control
of something like your landing light where the
author might say "active hi", "pull up to bus",
"high side switched", etc.
Discrete levels in both the power and digital worlds
are not subject to interference from small noises
that might exist on the selected ground for a pull-to-
ground push-to-talk line. Many thousands of radios have produced
performance as advertised when their mic jacks were
simply grounded to airframe at the jack's mounting.
Of course, in our legacy 3-wire microphone architecture
this does put transmit audio at-risk for picking small
noises that may exist in currents that flow on the
airframe . . . hence a potential ground loop that
manifests in noise heard on transmitted audio while
those same noises had no effect on getting the transmitter
to become active with the PTT button.
I have often advised builders to "follow the manufacturer's
instructions' when it comes to dissecting the designer's
intent for installations. In the SL-40 wiring excerpt
[img]cid:.0[/img]
We see that microphone and headset jack grounds are brought back
to the radio on their own wires . . . good practice. This
also means that the "pull down" on TxKey line by PTT buttons
on wired into these jacks will share that ground line wiht the
mic. This same drawing also shows "yolk mounted transmit buttons"
with an undefined ground. This is because the discrete control
line is not subject to the ground loop contamination and MAY
be grounded anywhere . . . which includes the option of taking
the wire all the way back to share a ground with the radio. Same
condition exists for the Intercom Selector Switch.
Bob . . .
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stearman456
Joined: 14 Aug 2010
Posts: 49
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| Posted: Thu Aug 30, 2012 12:21 pm Post subject: Re: |
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Thanks guys. It's steadily getting clearer!
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