Re: gEDA-user: powermeter board, with less ground planes :-)

[Joerg <joergsch@xxxxxxxxxxxxxxxxxxxxx>]

DJ Delorie wrote:
>> Isn't that whole outside perimeter plane GND?
> 
> Yeah, but I usually try to keep the caps closer to the ground pins as
> well as the vdd pins.  A lot of the chips I usually deal with (like
> the R8C) have the power pins near each other so you can bypass right
> at the chip.
> 

It's normally done the other way around. A good ground plane is seen as 
a zero impedance structure since this is the whole purpose of providing 
that plane. Caps are placed right next to the pin they are supposed to 
decouple. The path from the cap's GND via to any other ground (including 
chip GND) is considered to be a nearly perfect RF conductor.

Traces from the pin to be decoupled (bypassed) to teh cap should be as 
short as possible and as fat as possible. Nothing wrong with making a 
small plane out of that because it provides a small additional "courtesy 
capacitance", for free, to the ground plane below.


>>> Nope.  It's inside a metal box with all the circuit breakers.
>> That makes it pretty safe. But I did have a situation at a client where 
>> this wasn't enough. Cell phone noise made it in via the cables.
> 
> Hmmm... I'm not sure I need to worry about that.  The current sensors
> are 100% differential, the digital signals are slow compared to the
> pcb size and have series resistors, and I'm only using this for
> personal benefit.  But then again, I'm also doing one hand-made
> prototype first ;-)
> 

In their case signals were slow, too. But GSM does those bursts when 
connecting to a cell tower, rat-tat-tattatat. The RF got demodulated and 
you could see those slow bursts right in the data. Heck, we could almost 
derive the handshake sequence of that starting GSM connection from 
looking at the data.


>>> The two *.sch I posted are all there is; I have a Makefile that just
>>> renames the one channel to the other fifteen of them.
>> That's cheating :-)
> 
> No, that's *scripting* :-)
> 
> I even have a PCB script to copy all 16 of the layout blocks to a
> blank board, but now that it's almost done, it's easier to make 16
> changes manually.
> 

It'll take me a while to migrate to let level of gEDA driving skills. 
But so far the programs themselves are quite intuitive in their user 
interfaces.

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.



_______________________________________________
geda-user mailing list
geda-user@xxxxxxxxxxxxxx
http://www.seul.org/cgi-bin/mailman/listinfo/geda-user