The author purchased a Casio PRO fx-1 calculator without magnetic cards intended for it. What they look like is shown . From the photographs, the author determined that their length is 93 mm, which is slightly longer than that of a bank card. Cards of this length exist, but are rare and expensive. But if you take a shorter card and stretch it more slowly, then, according to the author's calculations, everything should work out.
The problem turned out to be in the method of determining the speed of manual pulling during recording. The card is transparent, strokes are applied above the magnetic stripe. When reading, they are not used, the "tape constant" is determined by software. Therefore, if the strokes are sealed, the card will be write-protected.
Transparent cards exist, but they are also rare. The author decided instead of strokes on a transparent map to make gaps in an opaque one where strokes should not be. 85 slots measuring 3x0,5 mm are not easy to do, but the author has a CNC engraver.
The author made a DXF file, translated it into G-code and experimented with an expired map. Nothing happened, because on modern cards the magnetic stripe has a high coercive force - about 3000 Oersted. And the calculator needs a low one - about 300. It's like with DD and HD floppy disks.
It turns out there are CR80 cards that are similar in size but with a low coercive stripe. On the Casio calculator forum, the author asked for a photo of the original card next to the ruler. It turned out that he made a mistake in the measurements, and in fact the card is the same size as the CR80.
But by this time the calculator had broken down - it stopped responding to keystrokes. Turns out the batteries were leaking. Cleaning the keyboard board fixed everything.
When the CR80 cards arrived, the author put them in the engraver and got this:
The author engraved with a 20-degree cutter at low speed so that the plastic does not melt. It is better to take a 10- or 15-degree cutter.
At first, nothing worked. The author soldered the wires to the magnetic head and connected it to the oscilloscope. This is what the recording looks like:
And so - when reading, it means that everything was recorded:
The author decided that it was all about speed, and decided to swipe the card a little slower when reading. She read. Then he tried stretching both too fast and too slow - everything worked, and it is not clear why it did not work the first time.
In general, the author has learned how to make maps for this calculator. The cracks are cut out slowly, and even in two passes, but even after that you have to finish them manually with a scalpel. But everything works:
To make the same cards, you need:
- Clear CR80 cards with low coercive stripe on PVC backing
- (CC-BY 3.0)
- File with G-code for cutting slots (ibid., in the section with files)
- Engraver type CNC3020
Source: habr.com