[TowerTalk] [RFI] Subwoofer resolution

[Jim Lux]

At 10:13 AM 8/20/2007, Dan Zimmerman N3OX wrote:
>"It turns out that the dominant cause of the susceptibility was a pin 1
>problem!"
>
>It's not only microphones.  Our lab's data acquisition cards and
>breakout boxes have a pin 1 problem as well.
>
>Very popular manufacturer of such things so I'm sure we're not the
>only ones... but we are using a couple of hefty motors driven variable
>frequency drives in the vicinity of the sensors and acquisition
>system.
>
>We had a heck of a time cutting down the noise until we figured this out.
>
>It's a major problem, all this stuff in metal boxes that do 
>absolutely nothing!

Well.. the metal boxes DO protect things from dings and mechanical damage...

And this kind of thing is why I'd love to have more optical 
interconnects (e.g. TOSlink style) or Ethernet (which is transformer isolated).


For folks looking for ways to provide galvanic isolation (which can 
help with pin 1 problems), Analog Devices has some very cool buffer 
amplifiers that provide this in a monolithic integrated 
circuit.  They're the ADum series.. digital isolators with multi 
megabit capability (the usual opto isolator works fine for audio 
frequencies, but isolating multimegabit signals is a 
challenge).  They have isolated half bridge drivers and hot swappable 
I2C interface drivers too... handy for things where you want to 
control something at the end of several hundred feet of cable and 
you're guaranteed to have a big common mode voltage difference.

They're in the dollar or three each price category.

For analog signals, they have a 16 bit delta sigma modulator to turn 
a voltage into a 10 Mbps galvanically isolated data 
stream.  AD7400  $4 each in qty.. just the thing to send back that 
rotator feedback pot value..

Jim, W6RMK