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)

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.

PCB Business Card

I’ve been seeing a lot of printed circuit board (PCB) business cards on the internet these days, particularly on hackaday, so I decided to jump on the nerd bandwagon and make my own. I searched google images for inspiration and found this one, which I thought looked pretty awesome. So I copied the general layout, but with a few minor changes. First, I designed my own circuit using a Propeller chip, 8 0603 (very small) LED’s, and a surface mount (SMT) battery holder. Second, instead of having white text on a black solder mask, I put the QR code and text on the solder mask layer. That way, the silver board will subtly show through from underneath.

I put the order in to Gold Phoenix last week. I choose their normal 155 in2 deal. It’s a really good price - without any option it’s $110. In my case, I ordered their thinnest PCB material, and added black solder mask. The total came out to $130 with shipping to the US. Expensive business cards at $6 each, but I don’t anticipate handing out too many and it would have cost way more if I had ordered them from an American company.

Here’s the board as sent to Gold Phoenix.Gerbv render of the Gerber files sent to Gold Phoenix

As for the circuit, it really is overkill. I’m not actually going to be able to afford to populate the boards, but as long as I didn’t make any errors, it should work. The the propeller chip is $8, and all the other parts added to the price of the bare board will bring this card to almost $18.PCB business card schematic

Download the Eagle Cad files.

Update on Tuesday, November 16, 2010 at 17:36 by Jay Kickliter

Just came in the mail from Gold Phoenix. They came out better than I was expecting. I’m glad I went with exposed silver, instead of silkscreen, for the text and QR code. However, it’s a bit difficult to read under uneven lighting conditions.

Update on Wednesday, November 17, 2010 at 14:53 by Jay Kickliter

I now take back what I said about not using silkscreen for the QR code. I still like the look of the silver text, but if anyone wants to do this I suggest you put your QR code on the silkscreen layer. I tested it with two different iPhone models, and both had a hard time reading the QR due to reflections.

Also, I failed to mention how great of job Gold Phoenix did on the board. I have no affiliation with them, by the way, I’m just impressed with their work. A few board have some missing silkscreen for the part names, and there are a few pin-sized holes in the back solder mask on a handful of board. But, the black solder mask is awesome looking; the photo I took doesn’t do it justice. Very glossy. Until I solder up some cards, I have no opinion of their etching abilities, but from what I’ve heard they do a good job with an acceptable percentage of boards with electrical errors.

I love to buy American, but these Chinese made boards are an order of magnitude cheaper than anything I could get made here. And from submitting my order to receiving the FedEx package was just a hair over two weeks.