Abstract: A system for capacitively detecting the presence of a tape cassette within a vending machine or the like. The testing system within the machine employs an ac source connected to a source electrode and a detector connected to a detector electrode. A coded pattern is provided along the side wall of the cassette with a pair of series connected electrodes arranged to oppose the electrodes of the testing system. When aligned, the capacitances formed between the testing system electrode and the coded pattern complete an electrical circuit from the source to the detector through the cassette. The completing of the circuit indicator the presence of the cassette.