homemade EFIS system and EMI

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Morgans wrote:
"Evan Carew" wrote

Well, when last I did this, I remember the RF "bonding" tape was nickel

plated coper foil with a collodial silver stickey backing. As I
remember, it worked perfectly, if somewhat expensively.


Sounds similar to something you can get in the heating and cooling sections
of the big box hardware stores. It is thin aluminum tape with sticky on it.
Seems like reversing it once in a while, or at the ends would get the al to
al contact, to bypass the non conductive sticky.
I have a feeling this would suffer from the same problem that riviting
suffers from, namely small gaps.

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Evan Carew wrote:

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Morgans wrote:
"Evan Carew" wrote

Well, when last I did this, I remember the RF "bonding" tape was nickel

plated coper foil with a collodial silver stickey backing. As I
remember, it worked perfectly, if somewhat expensively.


Sounds similar to something you can get in the heating and cooling sections
of the big box hardware stores. It is thin aluminum tape with sticky on it.
Seems like reversing it once in a while, or at the ends would get the al to
al contact, to bypass the non conductive sticky.
I have a feeling this would suffer from the same problem that riviting
suffers from, namely small gaps.

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McMaster Carr sells copper tape 1/4" wide to 3" wide with conductive
adhesive. The adhesive surface resistivity is .oo65 ohms/inch. The
copper foil is .0014" thick. Adhesive thickness is .0035". A six yard
roll varies from ~$6 to $42 depending on width. 1" width sells for ~$15
for six yards part# 76555A714.

Gary Thomas

Thank you everyone for the input, now I am looking for some
prioritization. I received the new power supply from www.mini-box.com
and it is substantially better than the previous version
(http://www.mini-box.com/s.nl/sc.8/ca...it.A/id.356/.f ) however
I still get some noise in the radios. The new version is too big to
fit in the previous enclosure so it is sitting slightly apart from the
MB on its own.

I have started to jot down what the system wants to do, pictures and
status at
http://69.229.202.54:8080 Under the 'Image' folder one can see the
plane, the EPIA in the nose and the prototype ADC board.

So now I have a case that has to heavily part for the ATX power lines
to come into it & a non cased DC power supply. I have attached ferrite
beads to the power lines coming in/out with little improvement.

It takes time for many of the steps so I am looking for what you folks
think would be the 'biggest bang for the buck', or the right priority
to proceed with. (IE, build a brand new case for everything, build a
seperate case for the PSU, don't build a case right away but do X,Y,Z,
etc..)

Thanks once again for the brains helping noodle this over.

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JC,

My comments/questions interspersed with your message:

jcpearce wrote:
Thank you everyone for the input, now I am looking for some
prioritization. I received the new power supply from www.mini-box.com
and it is substantially better than the previous version
(http://www.mini-box.com/s.nl/sc.8/ca...it.A/id.356/.f ) however
I still get some noise in the radios. The new version is too big to
fit in the previous enclosure so it is sitting slightly apart from the
MB on its own.

I have started to jot down what the system wants to do, pictures and
status at
http://69.229.202.54:8080 Under the 'Image' folder one can see the
plane, the EPIA in the nose and the prototype ADC board.

So now I have a case that has to heavily part for the ATX power lines
to come into it & a non cased DC power supply. I have attached ferrite
beads to the power lines coming in/out with little improvement.
Stupid question here JC, but it looks like you are using a PC style
switching power supply [high noise] to power your standard ATX style PC
board. Since most of the important voltages going into an ATX board are
either 5V or 12V, why aren't you simply using regulators off the plane's
battery to supply the power? It would seem to me to be both cheaper as
well as inherently less noisy (not to mention lighter). You wouldn't
even have to do any special parts sourcing on these regulators as they
are redily available at you local radio shack (karmic regulators anyone?).

For a break out of ATX voltages, see the following link:
http://www.7volts.com/atx2.jpg

It takes time for many of the steps so I am looking for what you folks
think would be the 'biggest bang for the buck', or the right priority
to proceed with. (IE, build a brand new case for everything, build a
seperate case for the PSU, don't build a case right away but do X,Y,Z,
etc..)

Thanks once again for the brains helping noodle this over.


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Evan Carew wrote:

board. Since most of the important voltages going into an ATX board are
either 5V or 12V, why aren't you simply using regulators off the plane's
battery to supply the power? It would seem to me to be both cheaper as
well as inherently less noisy (not to mention lighter). You wouldn't
even have to do any special parts sourcing on these regulators as they
are redily available at you local radio shack (karmic regulators anyone?).


You still need the minus voltages hence probably still an inverting power
supply.


I'd try mounting both in the same case for starters filtering the input 12v
supply and see where you need to go from there.
John

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UltraJohn wrote:
Evan Carew wrote:


board. Since most of the important voltages going into an ATX board are
either 5V or 12V, why aren't you simply using regulators off the plane's
battery to supply the power? It would seem to me to be both cheaper as
well as inherently less noisy (not to mention lighter). You wouldn't
even have to do any special parts sourcing on these regulators as they
are redily available at you local radio shack (karmic regulators anyone?).



You still need the minus voltages hence probably still an inverting power
supply.


I'd try mounting both in the same case for starters filtering the input 12v
supply and see where you need to go from there.
John

There are many different voltages coming from a power supply. Here is a
quick breakdown of what the different voltages do:

* -5V - Legacy ISA
* -12V - Legacy ISA, Serial Ports (including PS/2)
* +3.3V - Motherboard Logic, AGP, PCI
* +5V - Motherboard Logic, Drive Logic, PCI, ISA
* +12V - Fans, Drive Motors, PCI, ISA
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Thanks for the input.
Perhaps going with a linear power supply would be the way to go, I did
not as there are already three switching DC-DC power supplies on the
MB, the power efficiency is less than 50% for linear and I would have
to deal with the heat issues. I could just string a bunch of LM78xx and
LM79xx to get the required positive and negative voltages.

I've created a seperate smaller case for the PSU as creating a new
single case would have taken longer and I don't know about what level
of cooling issues I will have. I've noticed the PSU manufacturer (not
surprisingly) has reducd the MTBF when it is in hotter conditions. (but
hey perhaps I could use the heat to warm my cold toes in the Long Ez)
If the weather clears tomorrow I will go flying and measure how much of
a problem I have with it operating.

Thanks for the continuing input.

jcpearce wrote:

Thanks for the input.
Perhaps going with a linear power supply would be the way to go, I did
not as there are already three switching DC-DC power supplies on the
MB, the power efficiency is less than 50% for linear and I would have
to deal with the heat issues. I could just string a bunch of LM78xx and
LM79xx to get the required positive and negative voltages.

I've created a seperate smaller case for the PSU as creating a new
single case would have taken longer and I don't know about what level
of cooling issues I will have. I've noticed the PSU manufacturer (not
surprisingly) has reducd the MTBF when it is in hotter conditions. (but
hey perhaps I could use the heat to warm my cold toes in the Long Ez)
If the weather clears tomorrow I will go flying and measure how much of
a problem I have with it operating.

Thanks for the continuing input.
The LM79XX's will do you no good unless you have a source of negative
voltage to feed them. This generally will mean a dc to dc converter which
generally means switching regulators. Try putting your current powersupply
in a case and attach it directly to the MB's case and use feedthrough
capacitors in the common case bulkheads to feed the dc voltage in. Put
fedtrough caps and ferite beads on the dc in to the powersuppply case.
Cheep and will get you a good start to eliminating the noise.
John

John wrote:

jcpearce wrote:

Thanks for the input.
Perhaps going with a linear power supply would be the way to go, I did
not as there are already three switching DC-DC power supplies on the
MB, the power efficiency is less than 50% for linear and I would have
to deal with the heat issues. I could just string a bunch of LM78xx and
LM79xx to get the required positive and negative voltages.

I've created a seperate smaller case for the PSU as creating a new
single case would have taken longer and I don't know about what level
of cooling issues I will have. I've noticed the PSU manufacturer (not
surprisingly) has reducd the MTBF when it is in hotter conditions. (but
hey perhaps I could use the heat to warm my cold toes in the Long Ez)
If the weather clears tomorrow I will go flying and measure how much of
a problem I have with it operating.

Thanks for the continuing input.
The LM79XX's will do you no good unless you have a source of negative
voltage to feed them. This generally will mean a dc to dc converter which
generally means switching regulators. Try putting your current powersupply
in a case and attach it directly to the MB's case and use feedthrough
capacitors in the common case bulkheads to feed the dc voltage in. Put
fedtrough caps and ferite beads on the dc in to the powersuppply case.
Cheep and will get you a good start to eliminating the noise.
John

About $1.00 a piece from a couple sources I checked. So about $7.00 for the
PS voltages plus the dc input. (although some are sold only in 10 lots) if
you have multiple projects to use them up in you can order 100 quantity for
about $.50 each.
John

John wrote:

Thanks for the continuing input.
The LM79XX's will do you no good unless you have a source of negative
voltage to feed them. This generally will mean a dc to dc converter which
generally means switching regulators. Try putting your current
powersupply in a case and attach it directly to the MB's case and use
feedthrough capacitors in the common case bulkheads to feed the dc
voltage in. Put fedtrough caps and ferite beads on the dc in to the
powersuppply case. Cheep and will get you a good start to eliminating the
noise. John

About $1.00 a piece from a couple sources I checked. So about $7.00 for
the PS voltages plus the dc input. (although some are sold only in 10
lots) if you have multiple projects to use them up in you can order 100
quantity for about $.50 each.
John


Just checked Newark Catalog They have an interesting item:
A feed through teminal block with built-in filter capacitors
part # 95F895X
where x = number of terminals from 2 to 6.

Just something interesting to look into.
They have a lot of ideas for cap/ferite/filter ideas.
John