homemade EFIS system and EMI

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

John wrote:
wrote:


isn't there a step down treansformer taking 110vAC down to 12vAC then
rectified to 12vDC????


Steve
A&P and Computer Guru (and very interested in your Idea)


All kinds unfortunately this is for aircraft use, he's starting with 12v DC
(transformers don't work with DC) and needs to get +-12v +5 and +3.3v all
DC.
John

John,

I think you'll find that the -12V is used only in "legacy" PC design for
ISA busses, or serial ports (which he probably isn't using).

Evan
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.0.6 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFCEgqopxCQXwV2bJARAvUpAJ9QJP/GjpzrhRBgI73a8UrVyWBD+QCgsgGj
ONCHJdB56/BtoKbGC18OFS4=
=Lq2H
-----END PGP SIGNATURE-----

All kinds unfortunately this is for aircraft use, he's starting with 12v
DC (transformers don't work with DC) and needs to get +-12v +5 and +3.3v
all DC.
John

John,

I think you'll find that the -12V is used only in "legacy" PC design for
ISA busses, or serial ports (which he probably isn't using).

Evan


Yes I did a little research on it and the only thing the negative is needed
for is the rs232 serial ports. for this you can get a $1.50 ic to convert
+12 to -12 V low current.
That said, what I'd do is get a 1.5 amp 5v TO-3 regulator and a 1 amp TO-220
regulator along with one of the TO-220 adjustable 1 amp regulators for the
3.3 v and run it all off the 12V (highly filtered) input. That said,
(again) you might have problems with th 12V regulator if the input drops
below 13.8V! So you might need to use a separate battery for it and diode
isolate it from the aircrafts electrical systm and have it charged when it
exceeds the 13.8 volt figure.
John

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

John,

I wonder if we are trying too hard on the +12V issue. Couldn't you
simply let it float free with something like a MOV to keep it from
getting too high? If the voltage goes too low, a simple current limiting
sacrificial resistor (AKA fuse) would protect the equipment. You could
even use one of those self healing plastic fuses.

Looking at the design again, there won't be any hard drives or fans to
suck juice from this voltage, so the only thing it will be powering is
the PCI bus.

John wrote:



Yes I did a little research on it and the only thing the negative is needed
for is the rs232 serial ports. for this you can get a $1.50 ic to convert
+12 to -12 V low current.
That said, what I'd do is get a 1.5 amp 5v TO-3 regulator and a 1 amp TO-220
regulator along with one of the TO-220 adjustable 1 amp regulators for the
3.3 v and run it all off the 12V (highly filtered) input. That said,
(again) you might have problems with th 12V regulator if the input drops
below 13.8V! So you might need to use a separate battery for it and diode
isolate it from the aircrafts electrical systm and have it charged when it
exceeds the 13.8 volt figure.
John


-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.0.6 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFCEmEhpxCQXwV2bJARAvYPAKC5/3ys03DwDrklsBMYLKhzbeeNtgCdFDb/
7wukjwVF2NQz4kVSOqNayms=
=ohFv
-----END PGP SIGNATURE-----

Evan Carew wrote:

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

John,

I wonder if we are trying too hard on the +12V issue. Couldn't you
simply let it float free with something like a MOV to keep it from
getting too high? If the voltage goes too low, a simple current limiting
sacrificial resistor (AKA fuse) would protect the equipment. You could
even use one of those self healing plastic fuses.

Looking at the design again, there won't be any hard drives or fans to
suck juice from this voltage, so the only thing it will be powering is
the PCI bus.



Yes it probably wouldn't matter, an MOV wouldn't do much good but you could
still feed a 12V regulator I guess and when the voltage started to go above
that it would regulate and when below it would just slump. I don't think it
would hurt the regulator to take the input too low.
That being said you could build a low differential voltage regulator for the
12V line it's possible to do it with less than 1 volt drop you just can't
do it with the simpler 3 terminal regulators.
The main point is you get rid of the switching regulators and their inherent
noise. It also makes it easier to filter the PC's noise out of the supply.
John
PS I checked out his site and found it quite interesting. I use to program
with hex and then onto assembler when I started out with computers in 1976.
I had a SWTPC 6800 with a whopping ~800KHZ clock! You had to build the whole
thing from a kit soldering on the buss connectors (SS50 bus) ic's
powersupplies etc. It did not have video you had to use an external
terminal although I later build a video board for it and modified the boot
rom's to use it. I started with a Mega memory of 4Kilobytes and eventually
got up to 48Kilobytes. Those were the days!

"Evan Carew" wrote in message ...
John,

I think you'll find that the -12V is used only in "legacy" PC design for ISA busses, or serial ports (which he
probably isn't using).

Evan


What is the +12 vdc for?

Blueskies wrote:


"Evan Carew" wrote in message
...
John,

I think you'll find that the -12V is used only in "legacy" PC design for
ISA busses, or serial ports (which he probably isn't using).

Evan


What is the +12 vdc for?
serial ports, fans and disk drives mainly

John wrote:
I think you'll find that the -12V is used only in "legacy" PC design for
ISA busses, or serial ports (which he probably isn't using).

What is the +12 vdc for?

serial ports, fans and disk drives mainly

And nowadays CPUs.... late last year I upgraded a PC motherboard from
800MHz to to 2.4GHz by replacing the motherboard. The new motherboard
had an extra connector to provide 12V to the CPU 9Celeron, IIRC), so I
had to replace the power supply as well. I'm guessing that the CPU had
onchip regulators to provide the other voltages that it required.

Frank

Frank van der Hulst wrote:

John wrote:
I think you'll find that the -12V is used only in "legacy" PC design for
ISA busses, or serial ports (which he probably isn't using).

What is the +12 vdc for?

serial ports, fans and disk drives mainly

And nowadays CPUs.... late last year I upgraded a PC motherboard from
800MHz to to 2.4GHz by replacing the motherboard. The new motherboard
had an extra connector to provide 12V to the CPU 9Celeron, IIRC), so I
had to replace the power supply as well. I'm guessing that the CPU had
onchip regulators to provide the other voltages that it required.

Frank
Thats true. my athlon 64 bit has it too. it was originally for the P4 chip.
Although the project that was the focus of this thread delt with a mini-atx
case that does not have this. For that matter he was not using any disk
drives instead he's using an USB thumbdrive. so he probably could get away
with leaving out the 12v. I've never tried it so I don't know. Maybe this
weekend I'll pull out one of my older atx boards and see if I can get it to
boot without the other supplies.
John
PS Don't forget to emulate the pwr good signal!

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

As a general rule, if you are thinking of solidifying such a design, you
generally go out & purchase one of those hardened PC systems such as
PC104 or like. These systems come with features such as extended
temperature ranges, G tested, & slower clock rates so you don't have to
use fans. Most of the systems I have seen in this class also have slots
for CF cards & can get by on ~15 watts of power, or just about what your
average night light is rated for.

Evan
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.0.6 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFCFO6ipxCQXwV2bJARAoijAJ9uyFiGJsaghTBrb0hH+X cGVmSncwCfaoSK
0zoNS5oI56uVEBP39MDuFcA=
=KaXv
-----END PGP SIGNATURE-----

Thanks everyone. A brief update.
With the new power supply the mini itx people sent me the problem
almost went away, I was able to do flight tests with it but .... very
rarely it would still cause enough interference to cut into the
Radio's, something clearly unacceptable as sooner or later it would
happen when the tower would be talking to me.

So I suppose I will pursue the linear regulator route. John you
mentioned there was an IC to take 12V and invert it to -12v, do you
know the part #?

Before I read the recent post I had all the TO-3's to make one and was
going to try and just omit the -12V and see what happens as I could not
find out what this was used for, but I see in the posts it is used for
serial communication which I do use. The ADC board I built sends over
the sensors data via serial and I log all the GPS NMEA data via serial.


I like the idea of linear regulators, low noise and a low part count.
There should not be a heat problem as the nose of the Long EZ has
circulating air (which is a bane at high altitudes).

Looking at the ATX power supply specifications they state there is a
sequencing of voltages and when everything is OK, a PW_OK line is
dropped low. I would rather not get into sequencing and keep as much as
possible to the K.I.S.S. mindset. Does anyone have an idea on whether
this is truly important? I was hoping to just apply power and be ready.


Thanks again to everyone and the recent replies from John, Evan &
UltraJohn










Evan Carew wrote:
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

As a general rule, if you are thinking of solidifying such a design,
you
generally go out & purchase one of those hardened PC systems such as
PC104 or like. These systems come with features such as extended
temperature ranges, G tested, & slower clock rates so you don't have
to
use fans. Most of the systems I have seen in this class also have
slots
for CF cards & can get by on ~15 watts of power, or just about what
your
average night light is rated for.

Evan
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.0.6 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFCFO6ipxCQXwV2bJARAoijAJ9uyFiGJsaghTBrb0hH+X cGVmSncwCfaoSK
0zoNS5oI56uVEBP39MDuFcA=
=KaXv
-----END PGP SIGNATURE-----