tape contents detector - for digital cassette recorders

tape contents detector elektor april 1984 tape contents detector for digital cassette recorders M. Hafner BCD = binary coded decimal Figure 1. The circuit con- sists of three common-or- garden ICs and a handful discrete components. If these are all fitted on a small piece of wiring board, it will be possible with a little luck to house the detector in the recorder case. The circuit about to be described makes it possible to ascertain whether a digital casstte has been written into or not. It has been tested on a Commodore computer, with a ZX81, and with a Junior Computer. Not only does it enable you to distinguish between blank and recorded tape, but also, by alternate switching between play- back and fast forward wind — or rewind — to find the beginning of a program on the tape. When used with the Commodore or Junior Computers, the circuit shows by means of three LEDs whether the tape is blank (D2), contains a leader (Dl), or has been recorded (D3). The leader, or pilot tone,...