homemade EFIS system and EMI

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.