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Payphone card emulator

The following principle is the basis for building emulators of various cards. Since the memory of a smart card consists of a rewritable block and a non-writable one, and the telephone apparatus writes only to the rewritable region, what prevents us from reading information from a new card and saving it somewhere? Let the algorithm of the phone depends on the contents of the "write once" memory area, and it is individual for each copy of the card, but this area is unchanged! The only drawback of this method can be considered a rather large implementation complexity, but this is bought by the fact that based on this principle, emulators of almost all cards, including even SIM-cards of cellular phones, are implemented.

The implementation of the emulator on this principle can be done in two ways. The first is that a logical circuit is assembled, which implements the entire logic of the "apparatus-card" circuit. However, the scheme is quite cumbersome. The second method, which is described below, is based on the use of microcontrollers. In general, they propose to use microcontrollers from the PIC-series, however, to program such a controller is the highest degree. And for some reason everyone forgets about the estate available   controllers of other series, including ours, domestic. But I do not recommend using the latter because of their great and mighty size. The most acceptable in my opinion is the use of the MC68HC705K1 motorola controller. Firstly, it is quite easy to find, and secondly, it is cheap. So, everything is very simple. We assemble the programmer according to the scheme shown in the figure.


Programmer circuit

We read information (firmware) from a new card using the program with the help of this program and it is possible to record information on an empty card if it is not one-time

We program the controller by connecting it according to this scheme to the LPT port of the computer using the program. Download 32 kb

We assemble the emulator according to the scheme.


Calling card emulator circuit

The emulator is ready to go.