Touch Enabled Business Card

My last business card was too expensive to give out, so I designed this one using a Texas Instruments MSP430. Combined with the chip’s Pin Oscillator hardware, and TI’s Capsense Library, it wasn’t too difficult enabling capacitive touch. The great thing is that in software I can have it go into a low power mode and check the button every second or so. When it senses a a touch, it checks more frequently and only leaves low power mode to toggle an LED. I guess when you’re driving LED’s, low power sleep isn’t going to help much, but there are times when no LED’s are lit, even in the middle of a display routine.

I rushed to have these cards in hand before a job fair at my school. It was about two weeks between blank slate and getting the boards back from Gold Phoenix in China. I made a few dumb choices. Particularly, when laying out the board I have one of the LED’s on a different IO port than the rest. That makes it pain to write good code, since I have to do an if..then to determine which port to write to for a particular LED. Also, I didn’t lay out the LED’s in a sequential manner. Ideally LED1 should be attached to port 1.0, LED2 to 1.1, etc. I’m sure I had a reason at the time, most likely for cleaner routing, but that just made for uglier coding. Nevertheless, it works fine. Especially considering the prototype consisted of nothing more than one LED, and a penny with tape over it to substitute for the touch pad. 

Even using much cheaper parts and smaller batteries, I’d say it’s still too expensive. The parts probably come to $2, but the board is almost $8. I remember Gold Phoenix being cheaper, but I may be wrong. $110 for 155 in2 seems pretty good, until you start throwing in rounded corners, black soldermask, and very thin FR4. I think it’s about time to start looking for a new Chinese PCB manufacturer. Am I the only one receiving emails from Peak PCB? Has anyone else tried them? 

Downloads

• Source Code (mspgcc)
• Design Files (Altium)
• Schematic (PDF)

Eagle CAD and FreeRouting.net

Eagle Cad is a necessary evil to me. It’s the only usable PCB design software  I know of for OS X. Plus, there’s an abundance of parts libraries out there. Beside its sometimes horrible user interface, my biggest complaint is its autorouter. Luckily there’s a website, FreeRouting.net, that has an excellent online autorouter. It takes a little trial and error to learn how to use it, but it does a much better job than Eagle. Here’s a video I made showing you the basics to routing your Eagle design at FreeRouting.net.

Eagle CAD from Jay Kickliter on Vimeo.

Update on Monday, July 16, 2012 at 7:41 by Jay Kickliter

Update. I’ve since moved on to Altium Designer. It’s much more expensive, but I was able to get a student license for about $150 if I remember correctly. On the negative side, I have to run Windows in Parallels to use it. Although its autorouter is a little better than Eagle’s, I hardly ever use it. Altium has pretty good semi-auto routing with push and shove, allowing me to hand route almost anything. Mind you, I haven’t yet tried to route a board with a 320 pin BGA yet, but with fan-out and a multi layer board I suppose even that is hand routable.

The real test come when my student license runs out. I don’t know what I will use then. Someone who’s opinion I respect swears by CADInt. I downloaded it. It seems almost primitive in it’s simplicity, but maybe that’s good.  I might give it its day in court again.

PCB Business Card: It Works!

My PCB business card works now. Check it out. Please see my previous posts for more information, and leave a comment if you need help modifying the Eagle CAD files to make your own.

If you haven’t read any of my previous posts, I’d like it to be clear that I borrowed heavily from Mike Puchol’s layout and ideas.

I was very wary of the Propeller Chip’s ability to run of a coil-cell, since it’s rated at 3.3 V. I asked about the feasibility of doing so on the Parallax forums, but didn’t get much information. I guess someone needs to do the testing. My design uses a CR2032 coin-cell. As an aside, that means 20 mm x 3.2 mm. They’re rated at 3V, but I find it’s more like 2.9 due to the relatively high internal resistance of these cells. They really aren’t meant to supply more than a trickle of current, in the µA region. In this design, I coded the LED’s so only one is lit at a time, and they sink about 2 mA @ 2.9 when on. I’d be surprised if the circuit could still run if I removed the decoupling capacitors.

The code is very ugly and hard-coded at this point, but I will provide it anyway.

Download the DigiKey bill of materials.

Download the Eagle CAD files.

Download the Spin code.