So apparently I don't know how to make a layout for a solder-bridge.
Any guidelines that someone could point me to, or guidance would be
appreciated. Would a simple absence of soldermask be sufficient to
make the bridge easy to establish? You're going to be in there soldering
the IR components anyhow, it would be easy to drag the iron across
each spot along the way, but it needs to be easy to establish, rather
than the struggle that I've currently got going.
In my double-sided footprint for the finger switches I'm relying upon
a set of solder bridges to allow the cathode and anode of each IR LED,
and the collector/emitter of each phototransistor to be connected to
either hole - this allows mounting them from either side of the PCB.
I knew that the layout was going to be small - I made two 0.040x0.040
pads separated by 0.010" naively thinking that it would be hard to
avoid bridging two pads that close together. I am still a bit stunned
that it is a real bugger to get solder to bridge that gap. It turns out
that I also struggle with arithmetic, as I am startled at the number of
these bridges I've made.
Each switch requires that 4 bridges be made (Anode, Cathode,
Emitter, Collector). There are 40 switches in the finger assembly.
I've 160 of these that need to be made!!!
So, I've ordered a bunch of 0603 bridges from Digikey. I also invented
a new unit of currency: The millicent; as in: "In bulk, these bridges cost
78 millicents.". I'm going to press forward with the manual placement of
these 0603 components, but I'm not exactly excited about it. If I had
planned on this, I would have a footprint that was a closer match, with
0805 components, and would have had a stencil cut. Now that I have a
bunch of components already populated, manual is the only option.
Oh well. Onward.
In other news, the last of my 3D-printed parts from Shapeways shipped
today, so I should have them by Wednesday. I've got 7 finger-switch
assemblies completely assembled, and have made the metal clips to
complete the last one when the parts arrive.
The last batch of parts I received from Shapeways was a bit different than
the parts I had received from them previously. This batch was on the high
side of their tolerances or maybe a bit beyond, and had a much more solid,
hard surface. The previous batches had a friable surface layer that was not
well attached.
The fact that these parts were a bit larger necessitated more manual re-work.
I had to drill (with a pin-vise and tiny drill bit) open the holes for the IR
component leads. I had to trim off material in several places on all of the
levers for the center switches in order to get the lever to clear the carrier.
I had to trim some of the N/E/S/W keys. It is still an amazing bit of technology...
I just wish it was perfectly consistent!
Saving the best for last: I am able to read switch states! I've got the IR components
for the center switches on the index and middle fingers populated on the I/O
expander side of the board and am able to read switch states through the I2C
link. I'm geeked that it is alive.
It is getting there. Pics once the parts are all mounted.