Homebrew PCBs

Stefan Trethan wrote:
> I'd say it would probably work in a vertical tank, but moving the PCB
> would add complexity to the holder.

I agree. The complexity and other problems (corrosion of mechanical 
pats, vibration, ease of fastening the PCB) could easily outweigh any 
advantage.

> Uniformity is rotten in my tank too, especially since some of the
> holes in the bubbler hose seem to deteriorate over time leaving a few
> powerful streaks of bubbles. I'm sure it takes as much time again to
> complete the board as it takes to etch the first few spots bare, if
> not more. That sounds awful, but with the stuff i do (usually no
> smaller than 8mil) it doesn't seem to be a problem.
> 
> If there is a way to improve it, without too much fiddling about, i'd
> surely impement it. I was thinking about replacing the hose with a
> artificial stone type bubbler. Those seem to give better uniformity.
> 

There is the question of big bubbles verses small bubbles.

* Big bubbles agitate more because they more faster and displace more 
solution as they rise.
* Small bubbles are good for aeration, because they have more surface area.

I'd probably say big bubbles work better for uniformity because of the 
increased randomness. The good news is that big bubbles can be generated 
by a home made air tube. Drilling some 1mm holes every inch or so into a 
piece of rigid PVC pipe. The ends are sealed by heating over a flame and 
clamping in a vice to fuse the ends. your rubber air hose is inserted 
tightly in the PVC tube through a slightly undersized hole.

To avoid the whole thing floating up when you supply air, just lay down 
on top of it a couple of quarts rocks or glue some old broken ceramic 
tiles to it (neutral cure silicone bonds very well to roughened PVC).

The trick is not to drill too many holes and to have the tube exactly 
horizontal so air exits at equal rates from each hole.