If you haven't yet read part one or two of this series, find them here:
With all of the key design decisions under my belt, it was time to build. I ordered the boards and parts myself, then hopped onto our website quote engine and placed a kitted order. At the time, I hadn't had anything built for a while, so it kind of freaked people out to get an order from within the company. When I do this, I like to go through our web system, just like any other customer, which sometimes causes a bit of a "we traced the call, and it's coming from inside your house..." moment.
Anyway, we didn't have any problems with the build. Fortunately, I took my own advice and carefully labeled the LED polarity. LED polarity marking "standards" are so unstandard, that extra caution is always a good thing. Anything to reduce ambiguity is welcome.
My calculations suggested that I should get six to nine months of battery life with a few cards being pulled per day. After running the blue LED version for about three months, I was satisfied that battery life would be sufficient. That was good timing, because at about the same time, I was down to about two weeks before the show that I was planning for (one of the Embedded Systems Conferences).
Again, I sent an order through our website. This time a full turn-key, using PC boards from Sunstone. And, this time, no one was surprised by seeing an in house order. I ended up with plenty of time to program the boards before the show, and was ready to give them away for our in-booth contest.
Since that time, I've left a blue/red card holder and a green/red card holder on my desk with the original batteries. After about a year and a half, the battery voltage dropped enough that the blue LEDs no longer show. The red and green, with a lower forward voltage, are still going strong.
Here are the final specs:
- 1.5" x 3.5"
- Two CR2032 coin cell batteries
- Has a Microchip in circuit (ICSP) programming port
- Has an I2C/SPI port
- Microchip PIC18F46k22 microcontroller
- Freescale MMA8452 3 axis accelerometer
- Recommended capacity, 10 cards
Next time, I tell you what you need to do to get one of these limited edition Screaming Circuits electronic business card holders.
A farmer is someone out standing in his field