I design and build electronics at home, late at night when the spiders are out, and by day, I put my hours into Screaming Circuits. My job here doesn’t involve building things. I’m the marketing department, but I like to keep as much manufacturing smeared all over me as is possible. Here’s one way I do that.
Business cards are a bit of an anachronism today. I don’t give out many, this being the 21st century and all, but I still need some on my desk – I guess to look businessy or something. No one’s ever given me a cheap card holder with their logo on it, and I don’t want to just scatter cards around. So, why not combine my need to display business cards on my desk with my compulsion to create electronic things? With that thought in mind, I decided to build an electronic business card holder. Of course, I first had to decide just what an electronic business card holder would be.
Here’s what I came up with:
- It should be small, about the size of a business card
- It should have a lot of blinky lights
- It should do something when a card is removed
- It should have a long battery life
- It should use tiny parts to show off our manufacturing capability a bit
- It should be 100% buildable within our electronics manufacturing process (meaning it should be just electronics; no bolts or case)
That’s not a long list, but does involve a few decisions. I’m pretty familiar with Microchip PIC processors, so that would be a logical choice to drive the thing. Arduino compatibility would be cool, but I’d have more trouble with battery life, and the PIC microcontrollers come in some pretty inexpensive forms.
I’d recently been using a variant of the PIC18F46k22 on another project. I comes in a 5 x 5mm QFN package and can be purchased for less than $3 in small quantities. it has plenty of I/O and can be set to a very low power sleep mode. I settled on that MCU and a CR2032 coin cell battery for power.
Rather than add any extra hardware to hold the cards, I came up with an arrangement of pin headers and small push-button switches. (as in the photo below right). One header is the six-pin Microchip in-circuit programming (ICSP) header, and the other is a six-pin I2C/SPI header. Not that I need I2C or SPI, but with that, you could turn this into a robot business card holder or something.
I considered a light sensor to detect when a card is being picked up, but that would require leaving the A to D powered up, and it would be less reliable due to changes in lighting. I looked around my junk box at home, and found a Freescale MMA8452 3 axis accelerometer in a 3 x 3mm QFN package. It also has a decent low power mode, and can be talked to over I2C.
Some 19 GPIO pins remained open, so naturally, I had to put in 19 LEDs.
Stay tuned for my next installment, where I’ll go through some of the design decisions. At the end of this series, I’ll be giving out 10 of these, so stay tuned to see how you might be able to get one.
If you dreamed you saw the silver spaceships flying
That’s a okay. They’re RoHS compliant