I have the BBC micro version of this interface, along with the documentation and the original program disk. It is clear that the programs were translated from another micro's BASIC, for example there's a program to make a robot arm move the disks for a Tower of Hanoi, the program srts up arrays to handle the parameter stack for a recursive subroutine call, even though BBC BASIC has named procedures with formal paramterrs. Anyway, I've traced out schematics for the BBC version, the others may be similar. Here are some general comments : It plugs into the BBC user port, and used the 8 data lines only. There are 8 switch inputs. These feed buffers (a 4050 + half a 4071) and drive LEDs so yo can see the state of the inputs. They also go into a shift register. This links to 3 lines on the user port -- clock, load-enable, and data out. The first 2 are outputs from the computer, the last is an input to the comuter. Another shift register (4094 I think) is used for motor output. It uses the same line on the user port for the clock signal, and 2 more outputs One is the seiral data input to the shift register. The other latches the shift register contents (the 4094 includes a latch with 3-state outputs). Oh yes, the clock line also triggers a 555 timer (OK, half a 556, but it's the same thing). This controls the OE line of the 4094, and disables all the motors if the interface gets no clock pulses for a certain time (half a second or so). This prevents the motors from running if the program crashes. The outputs of that 4094 go to some full-H driver ICs -- TLE4201 according to my notebook. These drive some bi-colour LEDs (so you can see what the motors are supposed to be doing) and also the motor outputs to the model. There are 2 variable resistor inputs, and they're strange. Each variable resistor forms the timing resistor of a 555 monostable. These are separately triggered by 2 more lines from the user port. The outputs of those monostables are ORed together, and the output of that controls a 555 astable. The output of that astable, therefore, consists of a pulse train, the number of pulses depends on the value of the variable resistor connected to the monostable that was triggered. And that signal is fed into the last line of the user port, where it's counted by one of the counters in the 6522 VIA used for the user port. The external connections to this interface consist of : A 20 pin ribbon cable and socket to plug into the BBC user port A 20 pin header accessible through a hole in the case. This takes a ribbon cable to the model. It carries the 8 motor lines (2 lines each for each of 4 motors), 8 switch inputs, 2 variable resistor inputs, and 2 5V lines (common for the variable resistors, common for the swtiches). A 20 pin hgeader hidden away inside. Only a few pins are used, this carries the clock, input SR load, Output SR latch, the serial-in to the input SR and the last data bit from the output SR. It can be used to extend the interface to more than 8 switches and 4 motors, but the driver software would need rewriting, and AFAIK this was never used 5 fischertechnik sockets. One is logic ground (marked with an upside-down T). The otehr 2 are 2 pairs for power supply inputs. They were designed to link to a fishcertechnik transformer, you need a DC supply of 7-10V. It's used directly to power the motors, rgulated down to 5V for the logic. You only need to use one set (particularly if you have a nice bench supply...), and there are internal protection diodes if you connect the supply backwards. FWIW it took me under an afternoon to trace out schematics and sort the whole thing out... Let me know if you want me to look further. I can give pinouts for the connectors on the BBC interface, for example (the 'model' connector seems to be the same on all such interfaces). -tony