Nulldurchgangs-Detektor (2 NANDs)

This circuit can be used with tape recorders which have an audio-visual (AV) socket for synchronisation of a slide show with a recorded commentary. AV tape recorders are equipped with an extra head which is used to record a synchronisation signal on a separate track from the audio signal. On playback this sync signal is used to control the automatic slide projector. ff the tape recorder is equipped with an AV socket but not with sync signal generator and detector circuits then a separate slide synchroniser is required.