Self-made magnetic cards for the Casio PRO fx-1 calculator

The author purchased the Casio PRO fx-1 calculator without magnetic cards intended for it. What they look like is shown here . From the photographs, the author determined that their length is 93 mm, which is somewhat larger than that of a bank card. Cards of this length exist, but the roads are rare. But if you take a shorter map and drag it out 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 the manual broach during recording. The map is transparent, with strokes over the magnetic stripe. When reading, they are not used, the “tape recorder constant” is determined by software. Therefore, if the strokes stick, the card will be write-protected.

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Transparent cards exist, but they are also rare. The author decided instead of the strokes on the transparent map to make a gap in the opaque where the strokes should not be. It is not easy to make 85 slots with dimensions of 3x0.5 mm, but the author has a CNC engraver.



The author made a DXF file, translated it into a G-code and conducted an experiment with an expired card. Nothing happened, because on modern maps the magnetic strip has a high coercive force - about 3000 Oersted. A calculator is needed with a low - about 300. Here, as with DD and HD diskettes.



It turns out that there are CR80 cards of similar size, but with a strip of low coercive force. On the Casio calculators forum, the author asked for a photo of the original card next to the ruler. It turned out he was wrong in the measurements, and in fact the map is the same size as the CR80.



But by this time the calculator had broken - he stopped responding to keystrokes. It turned out, once in it leaking batteries. Cleaning the keyboard board fixed everything.



When the CR80 maps arrived, the author placed them in an engraver and received this:







The author engraved a 20-degree cutter at low revs so that the plastic does not melt. It is better to take the cutter 10-or 15-degree.



At first nothing worked. The author soldered the wires to the magnetic head and connected to the oscilloscope. This is what the signal looks like when recording:







And so - when reading, it means everything is written:







The author decided that it was all about speed, and decided to hold the card while reading a little slower. She read. Then he tried to stretch too fast and too slowly - everything worked, and it was not clear why it did not work for the first time.



In general, the author learned to make maps for this calculator. The gaps are cut out slowly, and even in two passes, but after that you have to manually adjust them with a scalpel. But it works:







To make the same cards, you need:

• Blank CR80 cards with low coercivity band on PVC backing
• Device for mounting the card in the engraver (CC-BY 3.0)
• File with G-code for slotting (ibid, in the section with files)
• CNC3020 type engraver