homemade EFIS system and EMI

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!

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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
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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:
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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
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jcpearce wrote:

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 #?


snip

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



http://www.jameco.com/Jameco/catalogs/c251/P38.pdf
This is one chip its a higher power version of the ICL7660/7662
TC962CPA
Converts +voltage to -voltage ie +12v to -12 volts or +5 volts to -5 volts.
About $2.50 a piece in single quantities.
They do use switching but with the low power should not be the problem that
the high power switchers in the +5 atx power supplies.
I think they're rated at 80ma 95+% efficiency it should be enough for rs232.
Also check weather your video uses - voltages it probably does. Put an
ampmeter in series with your - powersupplies to see what draw it needs.

As far as pw_ok is you could probably use a generic pnp transistor such as
an 2n2222 with a resistor from the + voltage to the collector, ground the
emitter and then a resistor from the + voltage to the base and a 10uf+
capacitor from the base to ground. connect the collector to the pw_ok. This
would keep the collector (pw_ok) high till the capacitor charged enough the
it would go to ground. You could also use a generic ic inverter to do the
same thing.


Hope this helps.

John

ps via has a board similiar to what your running but it is designed from
scratch to run from just 12v it retails for $183.00.

Hope this helps.

John

ps via has a board similiar to what your running but it is designed from
scratch to run from just 12v it retails for $183.00.


Product info:

http://www.logicsupply.com/product_i...roducts_id/174


VIA EPIA TC10000 Mini-ITX Motherboard (on-board DC-DC converter) $183.00

The ultimate platform for low profile networked devices, integrating an
onboard 12V DC-DC converter and horizontal SODIMM for complete system
design flexibility.

Measuring 17 x 17cm, the ultra compact VIA EPIA TC Mini-ITX Mainboard is a
highly integrated and configurable x86 platform with rich connectivity and
multimedia options that enables the development of a wealth of small, slim
and low noise networked systems. The rich built-in feature set of the VIA
EPIA TC alleviates the need for system developers to source extra
components, reducing cost and time to market.

VIA EPIA TC Specifications
• VIA C3™ processor
• VIA CLE266 North Bridge, VT8235 South Bridge chipset
• 1 x 200-pin DDR266 SODIMM memory socket, up to 1GB
• Integrated VIA UniChrome™ 2D/3D graphics with integrated MPEG-2
accelerator, motion compensation and DuoView support
• 1 PCI Expansion Slot
• 2 x UltraDMA 133/100/66 IDE connectors, direct DOM support (VCC set to
5V/3.3V on the 20th pin)
• 12V, 5V, 60W Max onboard DC-DC Converter
• VIA Networking Tahoe VT6103 Fast Ethernet 10/100 PHY-ceiver onboard LAN
• VIA VT1612A 2-channel AC'97 codec onboard Audio
• Onboard I/O Connectors: 2 USB connectors for 4 additional USBv2.0 ports, 1
Front-panel audio connectors (mic-in and line-out), 1 Serial port header, 1
LPT port-connector, 1 CIR connector (Switchable for KB/MS), Wake-on LAN
connector, 2 Fan connectors CPU/Sys FAN, 1 + 12V power connector
• Back Panel I/O: 1 DC-in jack, 1 PS2 mouse port, 1 PS2 keyboard port, 1
RJ-45 LAN port, 1 Serial port, 2 USB 2.0 ports, 1 VGA port, 3 Audio jacks:
line-out, line-in and mic-in
• Mini-ITX (4 layer) form factor 17 cm x 17 cm (6.7� x 6.7�)

Additional Information:
• This motherboard has an integrated DC-DC power converter wich needs a 12V
power supply. ONLY use a 12V, 5A (60W) power supply with this board. If you
plan on using this motherboard in a car or boat, you will need to use a
power stabilizer.

I built a test linear regulator power supply this evening and the TO-3
regulator bringing ~12v down to 3.3 Volts nearly burnt a hole in the
test board. I looked over the wiring which was OK so it looks like the
thermal output of bringing 12volts down to 3.3 for 3 amps is just way
too high. So so much for that idea (unless I am missing something)

I may just end up getting on the EPIA TC models as UltraJohn mentioned
and hope that their EMI/RFI solution is better. The plane battery
voltage is ~12volts idle and ~14 volts running, what is a way of doing
the "power stabilizing" necessary for the EPIA TC which requires
11.6-12.4 Volts? If I just put a 12V linear regulator on there the drop
off in voltage would prevent the system running off battery.

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jcpearce wrote:
I built a test linear regulator power supply this evening and the TO-3
regulator bringing ~12v down to 3.3 Volts nearly burnt a hole in the
test board. I looked over the wiring which was OK so it looks like the
thermal output of bringing 12volts down to 3.3 for 3 amps is just way
too high. So so much for that idea (unless I am missing something)

I may just end up getting on the EPIA TC models as UltraJohn mentioned
and hope that their EMI/RFI solution is better. The plane battery
voltage is ~12volts idle and ~14 volts running, what is a way of doing
the "power stabilizing" necessary for the EPIA TC which requires
11.6-12.4 Volts? If I just put a 12V linear regulator on there the drop
off in voltage would prevent the system running off battery.

JC,

Look at the specs for the part. They often require X many square inches
of copper, or equavelent in a heat sink to disipate the thermal energy
they throw away.

Evan
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jcpearce wrote:

I built a test linear regulator power supply this evening and the TO-3
regulator bringing ~12v down to 3.3 Volts nearly burnt a hole in the
test board. I looked over the wiring which was OK so it looks like the
thermal output of bringing 12volts down to 3.3 for 3 amps is just way
too high. So so much for that idea (unless I am missing something)

I may just end up getting on the EPIA TC models as UltraJohn mentioned
and hope that their EMI/RFI solution is better. The plane battery
voltage is ~12volts idle and ~14 volts running, what is a way of doing
the "power stabilizing" necessary for the EPIA TC which requires
11.6-12.4 Volts? If I just put a 12V linear regulator on there the drop
off in voltage would prevent the system running off battery.

You could use an external wirewound resistor(around 20 ohm), mount it to
your metal chassis, this should drop it to around 5v at 3 amp draw and will
make your voltage regulator a lot happier!
No matter how you look at it dropping 12+ to 3.3 v you'll have to disipitate
some heat somewhere.
John
Unless you use a switching regulator vbg.