Perhaps the simplest radio one can build is the crystal radio. Using a diode as a detector, the design generally uses less than 10 components and no battery, getting its power to run from the radio signal itself. [Billy Cheung] decided to build a crystal radio using a rather unconventional detector – the smart chip in a common credit card.
This is possible because the smart chip on many credit cards contains a diode. It’s then a simple matter of hooking up the right pads on the credit card to the rest of a crystal radio circuit, and you’re all set. Of course, [Billy] goes the whole hog, building the entire radio on a single credit card. Other cards are cut up to create bobbins for winding coils to form a variable inductor, used to tune the radio. Doing this allows for a much cleaner, thinner design, rather than using a variable capacitor which is comparatively hard to find. Turning the dial allows stations to be tuned in, and with a high impedance earbud hooked up, you’re listening to AM radio. Oh, and don’t forget an antenna!
[Billy] breaks down the details for anyone wishing to replicate the feat, going so far as to wind the coils in real time in his Youtube video. Cutting templates and other details are available on Github. While it’s not going to be the most replicated hack, as it requires the destruction of a credit card to achieve, we love the ingenuity. And, if society does collapse, we’ll all have a great source of diodes when the ATMs have all become useless. Video after the break.
[Thanks to Zane Atkins for the tip!]