[sdiy] Power input for 2xD / generic digital module

Seb Francis seb at burnit.co.uk
Thu Nov 13 20:22:35 CET 2008

 From the discussions I've had offlist about this, it seems opinion is 
in favour of using some kind of standard power connection, and making 
the module work off only +/-12/15V if this is all that is available.

For the voltage thing, I see no reason why I can't make it work with or 
without a +5V line.  In actual fact it won't require any more onboard 
regulators as the 5V would be used only for the 3.3V digital stuff and 
so there would be a regulator anyway.  I just need to do the maths and 
make sure the extra heat is going to dissipate sufficiently.

For the connector thing though, I'll probably be unpopular in suggesting 
that I don't want to go for either of the 2 standards that have been 
suggested to me ...

6 pin MOTM standard 0.156" MTA
This is really unnecessarily big IMO, taking almost 1" of board edge, 
and really unless you are plugging and unplugging modules a *lot* is 
probably OTT in terms of connector quality.

16 pin Doepfer standard
This is those horrible IDC ribbon connectors, and actually is also using 
quite a bit of board edge with half of the pairs of pins not used.

What I'd prefer is to use 0.1" pitch holes which would take Molex KK 
style (of cheaper equivalent) headers.  These seem of sufficient quality 
to withstand quite a lot of plugging and unplugging (Molex quote 50 
cycles for gold contacts or 25 cycles for tin, but I reckon I've done 
quite a few more than that with some of my modules while they've been 
under development).

So what are the thoughts out there?  How unpopular a choice would it be 
to have 0.1" pitch power connectors, using only 0.5" of board edge.  Is 
there a standard pin configuration already in use for -15V, AGND, DGND, 
+5V and +15V ?

I'm willing to be swayed, but I've also got the feeling that board edge 
space will be at a premium with all the tiny SMD components and a major 
amount of I/O.


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