Step 14: All Done!
Click here to see a video of the card in action - I'm afraid it isn't the world's most exciting video, but at least it will show you the card in operation. The dialling tones are very quiet, so you might need to turn your volume up to be able to hear it.
I did warn you that this took a little skill to make, and that it was very experimental - I get around a 50% success rate maximum at the moment when dialling on my home phone only by considerable tweaking of the mounting arrangements, and getting the number recognised accurately is highly dependent on a number of factors including your exchange and the mounting of the piezo disk, including the shape of the cavity cut inside the card. I may work on some improvements to this design, as it could get recognition close to 100% (have managed to do this now using the computer to drive the card as a simulator - for those who are very technically minded, I could redesign the card to drive the piezo with a pseudo sine wave rather than a square wave using filtered PWM signals, and increase the tone and space times as well.), although I probably won't bother doing this unless anyone was interested in getting these sort of cards produced in bulk, (which I doubt!). If you are still interested in how the design works, and are a bit of a techno-nerd like me, then check out the technical notes below to look at how this whole thing works.
In case you were wondering, this doesn't work from a mobile phone, as you need a dial tone from the exchange for it to recognise the DTMF tones generated, but as I mentioned, this is more of a novelty marketing exercise than a universal way to dial a number- certainly, it shouldn't be attempted unless you are really up for the challenge of improving the design. It is hopefully also a neat tutorial into some other useful techniques like designing enclosures for miniature electronic devices using ID cards and getting nice graphic overlays done. Finally, hopefully it will also inspire some ideas for other electronic business cards - certainly some of the ideas that people have emailed me privately since posting this have been fantastic, so I know this at least is happening! Time for you to now start designing your own version of the world's most technically advanced business card!