[SpHEAR-devel] PCB design (was: Pull requests)

[Fernando Lopez-Lezcano]

On 10/20/2017 05:09 PM, Tim Maloney wrote:
> I started this as a separate thread so I would not confuse it with the other.
...
> The two issues with the circuit board are the reversal of the transistors (they are marked upside down for how the circuit will be printed by a commercial service) and a discrepancy in where the ground is on the zapnspark diagrams.

Hi Tim,

Apologies for the delay. It has been crazy with several overlapping 
projects. I'm (slowly) wading back into microphone land...

Regarding the PCB design. I finally looked at it as I'm building more 
prototypes and milling boards. The problem is a "beginner's mistake" on 
my part, I routed all the traces in the _wrong_ layer. Bad printed 
circuit board designer, no cookie!

The traces are right now in the F.cu layer, they should be in the B.cu 
layer. That is why the component silk screen overlay prints on top of 
the traces. I never noticed because I'm milling my own boards and 
installing all components on the side that does not have traces and I 
don't have a printed silk screen layer...

See, for example, this thread:
https://forum.kicad.info/t/is-there-a-good-way-to-move-wireing-from-front-to-back/7889

I have not yet moved the traces to the right side of the board in git 
(seems easy enough) as I first need to make sure that the transistors 
are correctly wired when I do that (after all this is working for me 
when I build my own boards - if I move the traces to the other side the 
PCB will print correctly but I think the transistors will be wrong). 
Will take a bit of time and thinking.

> According to one set of documents one of the end terminals is supposed to be the “Hot” signal, yet it is printed on the circuit board with a pad that has a square end.  On the other end of the circuit board the square pad is the ground.  So does square end mean ground or hot?

The square pads are the common ground to the whole circuit (on both ends 
of the PCB). The "hot" or positive XLR connection point is the middle 
pad on the XLR side.

> My working mic suggests I found the proper ground.

I presume that is the case.
Best,
-- Fernando

PS: building another set of microphones, four and eight capsule...