ZXS1 cassette pulse cleaner - a cassette output signal cleaner for computers with single-frequency FS K

The ZX 81 is one of the most popular personal computers but it does leave a lot to be desired in certain respects, one of the most notable of which being its cassette interface. Any ZX 81 user who has had to type in a complete program again because it could no longer be loaded from cassette will confirm this. The pulse cleaner described here is designed to make such problems a thing of the past. This makes it a must not only for ZX 81 users but also for any other computer that uses a similar type of pulse/pause system for the cassette connection. ZX81 cassette pulse cleaner elektor october 1984 ZX81 cassette pulse cleaner Pm.. The Sinclair ZX 81"s cassette interface uses frequency shift keying (FSK) with a single frequency. The signal is built up of a number of pulses, a pause, a number of pulses again, another pause, and so on (see figure la). The number of pulses be- tween two pauses indicates the logic level: four pulses represent a logic zero and eight pulses are used to indic...