From: sleeper75se (sleeper75se_at_yahoo.se)
Date: 2002-01-18 08:08:23
--- In buildcheapeeg_at_yahoogroups.com, "Jim Meissner" <jpmeissner_at_mindspring.com> wrote:
> > in a PC. The ADC module would be the motherboard
>
> Let me discourage you from the idea of plug in boards.
> It would be better to hardwire the input board to the
> mother board and locate it several inches away from
> the digital noise sources. Let us see how this works
> before you have grand ideas.
Hi Jim,
It's not a very grand idea, I think, just practical if you have 8
channels. The motherboard would just be a backplane on which the
amplifiers and ESD protection sit, along with the DRL.
I can forsee two problems with this approach, though:
1. Since the connections aren't soldered, signal quality might suffer.
2. The amplifiers can perhaps disturb one another if they are stacked.
Is this correct? Or are there other potential problems?
> Very likely the input boards will have to be located in
> their own shielded box. Changing jumpers will be no problem.
> You will be changing more than jumpers in the first version!
> Forget digital - analog switches for a while also.
I can let the amplifier backplane and the ADC-module be two separate
boards, so they can be placed in different boxes, should the need
arise.
Those analog switches won't happen anytime soon, by the way. :-)
> The ESD resistors can be hung on the input connector.
> Do not go to the mother board, do not pass go!
> Also I noticed that the diodes on the shield driver are gone also.
Hmm, if letting the unamplified signals pass a second board lead to
trouble, (does it?) perhaps I should put the ESD-resistors and shield-
diodes back in on the amplifier board? The diodes are not a problem,
but two 1/2 watt (that's what I can get my hands on) carbon resistors
are *huge* on that little board.
Do you know why Linear recommends carbon resistors only? I know they
are very rugged, but won't regular thick-film (SMT) resistors survive
a ESD-pulse too?
> Don't let a few microvolts scare you. They just want a little
> respect. But seriously, I am quite willing to help. I have worked
> on projects that were much more difficult. We were measuring nano
> volts with very high accuracy.
> Even plain copper wire was not good enough and we could not even
> use low EMF solder. Everything had to be crimped. We had to use
> silver plated oxygen free copper and heatsink the connections
> together and protect them from drafts.
I guess it didn't go into volume production, then? :-) What were you
measuring?
> I think you are doing a great job here. If anything, you went a
> little overboard with the double ground plane and all the vias.
Actually, I think there should be more vias. ;-)
> Looks real professional!
Thanks! It's easy to do professional stuff with professional software
though. After I've routed all traces I just add a big polygon to the
board and the program does the rest. As for the routing... nothing
helps like a couple of thousand hours of training.
> The guard ring around pin 2 and 3 is a little tight!
> At some point it is easier not to solder them to the PC board
> traces. Just let them hang in the air and connect wires directly
> to the pins. That is called 3 dimensional sky hook wiring. Not
> pretty but it works.
Ah, yes, I've seen that before. Ok, If the PCB looks too ugly after
I've etched it, I will use that trick.
/Andreas
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:36 BST