Monthly Archive for May, 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.

Added MAX232 Breakout Board

Here’s a simple MAX232 breakout board for a breadboard, à la the FTDI-based board I made a few days ago. I haven’t etched it yet, but I would be surprised if it didn’t work.

The schematics and layout are available on ubbcom’s GitHub repo.

ubbcom Works!

Got it working very quickly after a couple of redesigns.

My first etch came out pretty iffy, as you can easily see:

So, I redesigned the board a bit and transferred it.

Ah crap, forgot to mirror my transfer. Let’s try that again:

Nice. The only sketchy trace was the one that connects to the RXD line, but I tested it and electrically, it’s okay. So, I assembled the board and planned to find a broken USB cable and solder it onto the 4 holes at the top of the board.

Unfortunately I couldn’t find a USB cable, so… I made my own by taking a random piece of 4-conductor wire and soldering a PCB USB connector to it.:

Yeah, that didn’t work so well. My computer recognized that a device was plugged in, but failed to talk to it. I think it might have had something to do with the fact that the cables weren’t stranded. Or, I may have killed the FTDI chip because I applied a fair amount of heat when I soldered it.

So, it was back to the drawing board. I designed a new board with a built-in USB connector so that I could just connect it to my computer by plugging it in directly or by using a USB extension cable.

I’ve discussed the MITERS etching process before. It’s pretty great. Basically, the steps are:

  1. Print out the board design onto glossy paper with a laser printer.
  2. Sand down the board you want to etch a little bit to roughen up the surface.
  3. Clean the surface with acetone.
  4. Put the printed design and the board together and stick it through the laminator.
  5. Remove the paper quickly under water. I discovered the technique is to scrub the paper away rather than to peel it; the transfer comes out usually nearly perfectly.
  6. Throw it in ferric chloride and swish it around for 10 minutes.
  7. Wash with acetone.

I wired RXD and TXD together and tested it out. It worked!

Afterward, I put some male headers onto the device and stuck it in a breadboard to create the demo video above.
I’m pretty sure the entire device can operate with just the FT232RL alone. The rest of the components on the board range from somewhat important (ferrite bead, filter caps) to purely asthetic (debug LEDs). I bet you could get rid of it all and it’ll work fine. It’s more expensive than a typical MAX232 design (which probably totals about $2.50), but it doesn’t require RS232, which is kind of a plus. I’ll probably make a cute little MAX232 breakout board in the future as well, though.

ubbcom: Etching Really Small Things

It’s almost time for me to graduate, so I decided to take a little time this weekend to do something other than freak out about making sure I have everything taken care of.

I was staring at a breadboard on my desk and it occurred to me that I’m always ripping up my MAX232 chip and associated components to save space for one project while putting it back so that I can use serial communication for the next project. So, I thought, why not make a decent breakout board that uses one of the FT232RL USB Serial drivers that I have lying around?

The design is very simple; it’s basically the same schematic as Sparkfun’s FT232RL breakout board. However, unlike that board, it’s designed so that it sits in the middle of the breadboard, using only 2 rows (and 4 pins). It also allwos one to use USB to power the breadboard.

First, I wanted to test to see if I could actually etch an SSOP28. They have an extremely fine pitch, so I knew it would be quite difficult to etch them. Using MITERS’s lamination method, I tried it out and had some decent success. I only have a picture of the final etch, but I’m convinced that with a little refinement (not to mention fixing the blatant bugs in the design), this design is totally etchable with minimal manual intervention. I had to clean up a few toner-transferred traces with a knife, but overall, the transfer process went well; the laminator applies a perfect, even amount of heat to the board and toner as it passes through and only takes a few seconds. For a design with such a small pitch, one of the issues is that the toner smooshed and covered a slightly larger area than it should have.

After I cleaned up the traces, I etched the board with very good results. It took a while (probably 15 minutes) to clear out the tiny little spaces between the SSOP traces, but it definitely worked in the end.

I’m going to re-route the board and etch a prototype that should theoretically work, hopefully, maybe, if the stars are aligned.

ubbcom’s github repo is here.