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)

EM Fields Reference

Here’s a reference I made for an engineering electromagnetics course I’m taking. I hope it can be of use to someone else. Both the PDF and LaTeX source file are here for download.

PDF

LaTeX

Energy Meter

My buddy Frank (the guy talking way too fast above) and I designed an open source energy meter. It is still in early beta, but Frank’s about to be commissioned in the Navy, and I have a three month Merchant Marine cruise coming up, so neither of us will have time to work on it for a while. Anyways, it’s pretty awesome if I do say so myself. It’s similar to the Kill A Watt, but it’s wireless, uses mesh networking, and is scalable from a metering a single outlet to service as building’s primary energy meter.

Features

• Uses current transformer for shuntless current measurements
• Wireless (ZigBee)
• True RMS voltage and current measurements, for accurate readings with noisy loads
• Power factor calculated with Fast Fourier Transform, with possibility of using FFT for Total Harmonic Distortion calculation
• 8 core Propeller microcontroller running at 80 MHz allows for lots of number crunching

Also, I wrote an OS X Cocoa application for an interface to sensors. Currently, it only recognizes one sensor, but with a little modification I’ll make it handle any number of sensors. We even configured the sensors to occasionally send current and voltage waveforms. That’s mostly eye-candy, but could be useful to a utility to identify problems or particularly noisy loads.

TODO

• Design a board that fits a standard size box
• Add the ability to switch out current transformer’s burden resistance on the fly, depending on amperage, to allow for a wider range of current. Currently we’re getting accurate measurements from 10 mA to about 12 A, after that it starts clipping at the input of the op amp. For a house, there’s a much wider range of currents.
• Find wireless modules that allow for huge mesh networks. Big enough for all the houses in a small town to pass occasional readings to the utility.

If you’re interested in getting involved, let us know. You can check out the live code at our Google Code page.

 Downloads

Schematic

Eagle CAD Files

Design Summary from APPA Conference

Propeller code