The sole signal needed by star-cycle is a pulse on one of the Raspi's IO-ports on every revolution of the pedal levers. My exercise bike has a tachometer generator, consisting of one reed-switch that is closed once per revolution. Normally, this switch is connected to the exercise-bike’s board-computer (via a mini TS-plug). For use with star-cycle, it is connected to the 3.3V pin and GPIO 7 on the Raspi's pin-head.
If your exercise-bike doesn't provide such a switch (or you don't want to modify it's circuits), it should be easy to add an external switch to the exercise bike: Simply glue a reed-switch somewhere near one pedal lever and stick a magnet to the lever so that the lever closes the switch once every revolution. The switch is then connected to the 3.3V signal and the GPIO 7 signal on the pin-head.
WARNING: Do not connect your exercise-bike’s circuitry directly to the Raspi unless you know exactly what you are doing, since both devices can be damaged that way.
The software is provided as a BlueJ project. The BlueJ-development environment, including the library necessary for using the Raspi's GPIO pins (namely pi4j), is already installed on recent Raspian versions.