Toy stethoscope giving sound of heartbeat from doll - has oscillator switched on by permanent magnet hidden within doll

摘要

The toy stethoscope contains a reed switch within its probe which makes contact when it approaches the field produced by a permanent magnet buried inside the doll. This switches on a multivibrator circuit which drives a diaphragm to produce the sound of a heartbeat in the ear tubes. The electronics, the diaphragm and the battery are contained within a box at the junction of the probe and the ear tubes. The doll has a vinyl skin covering the magnet.