Today's Message Index:
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1. 06:56 AM - Re: Re: p-lead signal conditioning or tach gen usage (Robert L. Nuckolls, III)
2. 07:35 AM - Re: magnetometer location ()
3. 08:12 AM - Re: Relays etc (RGent1224@aol.com)
4. 02:21 PM - Re: p-lead signal conditioning or tach gen usage (Craig Winkelmann)
5. 07:58 PM - GPS multiple feeds - how many? (Phil White)
6. 09:05 PM - Re: GPS multiple feeds - how many? (Kenneth Melvin)
Message 1
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Subject: | Re: p-lead signal conditioning or tach gen usage |
At 04:59 PM 11/1/2009, you wrote:
><capav8r@gmail.com>
>
>Bob:
>
>Put a scope on the tach gen output. The situation is the signal
>from the tach gen goes to a 5.1 V zener diode, then to a comparator
>against a reference voltage to generate a square wave.
>
>Attached is the picture of the waveform at low rpm (approx
>800). Note the spikes in the wave. Also, the voltage is near the
>zener voltage so the zener never gets driven into breakdown so that
>is why the unit has a flakey rpm reading at low
>rpm.
Agreed.
>So, would the waveform squaring circuit you posted in an earlier
>post work to square this waveform? If so, I have 28 VDC available
>in the aircraft. I'd need to use a 28-5 V converter chip to get the
>5 VDC on the collector as you drew it. Any suggestions for this?
I don't recall exactly what I sent you earlier
but this is probably similar.
Emacs!
This squaring circuit has a +0.6v threshold. Since
your 80mS, 5v trashy square wave goes above and below
ground, this will square it up nicely. The diode
keeps the negative excursions at high RPM from going
exceeding the zener breakdown threshold for the NPN
device.
Bob . . .
---------------------------------------
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
---------------------------------------
Message 2
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Subject: | magnetometer location |
Judson,
I recently mounted two of the Dynon type next to each other behind the
panel. The dealer said you "might" get away with it. Way too much
interference with stuff. they were way off. I then set them on the top
of the panel just to see the difference - wow, right on! ok, get them
out of the panel and over to the wings or maybe behind the seat. to keep
them separate I mounted them in the stub wing area on each side of the
Legacy. you must be very careful they are mounted at the same angle as
the unit. Put them where they won't get wet and where you have access to
get at them for maintenance. It's all about maintenance.
I find they are sensitive to everything, e.g. spars, landing gear,
pliers in your pocket etc. Get or make an extension cable (easy) and
give them their own space. You'll enjoy the better accuracy.
Glenn
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of
Judson Porter
Sent: Sunday, November 01, 2009 12:59 PM
Subject: AeroElectric-List: magnetometer location
<jdporter@elp.rr.com>
I'm using 2 EFIS units and could connect both to the same magnetometer
but wanted to have backup. Is there any problem mounting them next to
each other side by side. Will they interfere or cross talk with each
other?
Message 3
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David
No Problem that's what we're here for
Dick
In a message dated 11/1/2009 9:38:32 P.M. Pacific Standard Time,
skywagon@charter.net writes:
Dick,
Thanks for the web link.....
David
----- Original Message -----
From: _RGent1224@aol.com_ (mailto:RGent1224@aol.com)
(mailto:aeroelectric-list@matronics.com)
Sent: Sunday, November 01, 2009 7:10 PM
Subject: Re: AeroElectric-List: Relays etc
Try this site for a better price ie $2.49 ea
_https://www.surpluscenter.com/item.asp?UID 09110121075049&catname=&qty=1&
item=11-2275_
(https://www.surpluscenter.com/item.asp?UID 09110121075049&catname=&qty=1&item=11-2275)
They have lots of other goodies also
Dick
In a message dated 11/1/2009 4:44:00 P.M. Pacific Standard Time,
_nuckolls.bob@aeroelectric.com_ (mailto:nuckolls.bob@aeroelectric.com) writes:
Second, as a short cut to some thinking, I made a habit of checking
with how the auto industry wired things - you know if they had a device too
rich in current to switch alone, they used relays and the same principle
applies. I have never (well once) had to change a car relay since 1948 (and
it was corroded) so I guess my aircraft device (homebuilt) could stand it.
Bosch relays seem very reliable.
Just an idea,
An astute and accurate observation my friend. As a rule,
relays are considered to be some of the least reliable
devices in terms of failures per flight hour. Indeed
compared to transistors, capacitors and such, they are
way down on the totem pole.
So when you're working on a 200 ton ATC aircraft with
miles of wiring and tons of electro-whizzies that
get exercised 15 hrs a day for weeks at a time, one
minimizes the numbers of relays and picks them carefully.
Down-time on these aircraft is measured in thousands of
dollars per day.
In the automotive world, the cost of ownership and
magnitude of risk due to failure is much lower than
for complex aircraft. Light airplanes are certainly
higher risk but failure tolerant design can buffer
that risk.
Hence, relays need not be avoided where they make
sense. One doesn't want to put an ugly-beefy toggle
switch in right next to an ordinary 7 - 10A device
just to accommodate some heavier load. Relay buffering
is a good thing to consider . . . solid state relays
even better.
Fortunately for us, only things like pitot heat
(30A inrush), large landing lights (30-50A inrush)
and perhaps hydraulic pump motors (100A inrush)
are devices that give pause for extra attention.
Relays like this . . .
_http://tinyurl.com/yhrqnkz_ (http://tinyurl.com/yhrqnkz)
are designed and tested to survive under the hood
of an automobile. There are other examples in the same
family of products. They're made on totally automated
machines and are reasonably priced. Once
the system demands push much above 7A or offer
extra-ordinary inrush loads, a relay may be
an ingredient that fits your recipe for success
quite well.
Having said that, let's talk about any particular
situation where you think the relay is a potential
solution to a design goal. I about dropped my teeth
when I saw this picture the first time:
_http://aeroelectric.com/Pictures/Relays/TooManyRelays.jpg
_ (http://aeroelectric.com/Pictures/Relays/TooManyRelays.jpg) . . . and
these were part of an electrically dependent
engine's ignition, fuel and controls system!
"One is good" does not morph into "21 is better."
Bob . . .
---------------------------------------
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
---------------------------------------
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Message 4
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Subject: | Re: p-lead signal conditioning or tach gen usage |
Bob:
I can eliminate the comparator circuit if I get the output of the squaring circuit
to 5 VDC (TTL level). My thought is to use a Texas Instrument UA7805 Positive
Voltage Regulator and connect it to an available 12VDC source in the aircraft.
This should give me a stable 5.0 voltage source. At 5.0 VDC, the prior
squaring circuit diagram used a 4.7K resistor on the collector to limit the current
when the transistor is off. This should square off the signal and provide
a TTL level input to the EFIS system in the aircraft.
I can build this on a breadboard and test it in the lab and use a variable speed
power drill to rotate the tach gen.
If the above sounds reasonable, I'm off to order the parts from DigiKey. Thanks
for all the help and advice.
Craig
Craig
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=270633#270633
Message 5
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Subject: | GPS multiple feeds - how many? |
I am building an RV-10, and beginning to assemble and wire a panel. My
main GPS is a Garmin 396. I need it to feed my GRT EFIS, a Tru-Trak
autopilot, and a 406 MHz ELT. Will I have any problems with impedance
matching, or signal degradation if all 3 are fed from the GPS directly?
I don't know the input impedances of any of these fed boxes, or what
sort of power the Garmin can generate on its RS-232 feed.
I read the 2007 post about using a DB25 connector to facilitate the
multiple connections, but wonder if one needs a buffer or amplifier of
any sort to handle 3 outputs from one.
Phil in IL
Message 6
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Subject: | Re: GPS multiple feeds - how many? |
My Garmin 395, and now a 496, drives a Trutrak autopilot, Argus 5000,
and automatic position reporting transmitter perfectly well, without
any consideration of impedance compatibility. Consultation with Garmin
tech support had indicated that these portable GPS units are expected
to drive three devices without degradation of signal. and I can
confirm that. I tied together the five pins of a DB9 connector as a
"NMEA-bus", and it works well.
Kenneth Melvin, N669TJ, RV-9A
On Nov 2, 2009, at 7:38 PM, Phil White wrote:
> >
>
> I am building an RV-10, and beginning to assemble and wire a panel.
> My main GPS is a Garmin 396. I need it to feed my GRT EFIS, a Tru-
> Trak autopilot, and a 406 MHz ELT. Will I have any problems with
> impedance matching, or signal degradation if all 3 are fed from the
> GPS directly? I don't know the input impedances of any of these fed
> boxes, or what sort of power the Garmin can generate on its RS-232
> feed.
> I read the 2007 post about using a DB25 connector to facilitate
> the multiple connections, but wonder if one needs a buffer or
> amplifier of any sort to handle 3 outputs from one.
> Phil in IL
>
>
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