[elrom]

I want to populate half of a sigma 22 board, effectively making a sigma 11, but allowing for future expansion (i.e. i would be able to convert the 11 to the 22 when I need to).
 
I would essentially be making just the non-tracking side (i.e. the positive side) of the 22.
 
Thoughts? Any foreseeable issues with this?
 
thanks
 
~elrom

 

[amb]

You could do that, but you'd have to make a hack (have a look at the σ22 schematic and see how CR2 is connected, then compare to the σ11).  Also note that σ22's LED is driven across the two rails rather than from one rail to ground.
 
The σ22 is a bigger board than the σ11 so it might limit your casing options (e.g., σ11 is designed to slide into a Hammond 1455N160x but there is no way to put a σ22 in such a case).
 
You seem obsessed with using the σ22 with the M³ in some fashion...

 

[elrom]

haha yup. I'm cheap and want to have an economic upgrade path.
 
hmmm, i missed CR2's difference when I did my initial comparison of the schematics. 
Now im curious, how does CR2?
 
side note: I'm an ece who unfortunately has very little experience with analog.

 

[nikongod]

I think the most economic upgrade path has historically been, and as far as I can tell remains, building or buying gear that you can sell at a minimal loss with no fear of its failure at a later date. 
 
Make life easy on yourself, build the M3 with the s11.
 
If you want to go truly frugal build the M3 and use a wallwart with a point to point tread or the s25 crammed in the box. Alternately just use the wallwart and prey that PSR will pull you through (It kind of will, and kind of wont).