[Milkymist-devel] J21/J22 connector size
werner at almesberger.net
Wed Feb 29 15:59:20 PST 2012
Wolfgang Spraul wrote:
> How about routing the 2 analog line-out signals from behind the
> audio DAC to one of the two expansion headers?
That would need more than just two pins: audio has its own ground,
so you need at least three pins. We have two types of ground for
analog audio, the "fixed" ground and a floating ground. So if you
want to have both, that's already four more pins.
Splitting analog audio between J21 and J22 would give you the
number of pins but I wouldn't expect this to be nice for signal
> That way someone could build a (limited power, but still) speaker
> amplifier expansion board.
Oh dear, the USD 500 ghetto-blaster ;-)
> Or how about the S/PDIF roh mentioned?
That would be easier since there are only two signals and they are
relative to digital (main) ground.
Joerg suggested another use: remove one ground pin on each
connector such that it can be used for keying. This can be
accomplished by inserting a little plastic plug into the
connector. The parts (female 0.1" connector and a plug) look
Sorry about the poor image quality. Taking pictures of black
things a night is kinda tricky with a not too fancy camera.
On the expansion board or connector side, one would simply
cut the respective pin.
Joerg suggested to cut pin 4 of J21 and pin 1 of J22. With
this kind of keying, connectors could not be reversed, would
be harder to shift, and it would also be difficult to insert
something for J21 at J22 and vice versa.
We should probably still connect the "cut" pins to GND, just
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