Daily Archive for May 29th, 2012

2nd prototype of bcard: a little better, but not much

I redesigned bcard. Here’s what it looks like now:

After discovering that it’s basically impossible to vertically embed SMD LEDs into a board, I decided to try to see if it would be possible to use 3mm LEDs instead. So I switched those footprints. I also made the majority of the traces 20 mils thick to improve etching. Next, I moved to a 2-sensor design, so that theoretically you swipe your finger across a newly designed capacitive touch sensor and the lights will pulse. I like the design of the new sensor better; it fills up the space much more nicely. I had to reroute the entire board to make this new design work.

I kind of like the swirling pattern of the traces as they approach the micro. I originally intended to rotate the design so they wouldn’t swirl, but after looking at it, I kind of liked the design.

Anyways, I went to MITERS to etch it today. There were some good results and some bad ones.

First off, I completely forgot to include the outline of the battery holder cavity on the board outline, so I had to eyeball that.

The photo above shows my attempt to solder down the SMD components. I couldn’t find the really fine tip that I usually use and I was working with thick solder, so the result was very messy. I think that for production, I’m going to need to use the hot plate method.

If I use the hotplate method, that’d be a good time to try DIY soldermask. I’ve found it online; I think it might be fun to try.

Here’s a shot of the new battery holder, which uses copper foil. Copper foil does not work as a battery holder. I’m pretty convinced that I will not be able to make a reliable button cell battery holder, as much as I wanted to. So I’m probably going to buy one and add it to the board because I have no other choice. 🙁

The LEDs were a shitshow too. I’ve given up trying to embed LEDs into a board. It sounds easy, but it’s extremely difficult to do reliably. I’m going to have to figure out what else to do to make the board cool. This might mean major redesigns. Hopefully it won’t.

All in all, though, this is a completely usable prototype and I will attempt to do the programming for the touch sensing on it. Implementing the swipe motion probably won’t be too difficult; it’s a very simple state change. Hopefully I can take advantage of power saving features. I have some wires coming off of the microcontroller for programming as well as tabs for VCC and GND.

So, this failure wasn’t quite as bad as the last… I’m going to focus on programming the damn thing for a while. Then I’ll get back to figuring out how to resolve the remaining issues. Moral of the story, though: it’s basically impossible to do repeatable custom stuff on a PCB. My embedded battery holder idea was great in theory, but almost impossible to implement in reality. Embedded LEDs just won’t work right. Even if I could embed them, they aren’t lighting the card up enough.