Abstract: A speed sensor comprises a pick-up device mounted on the aluminum casing of a vehicle transmission, adjacent an existing ferromagnetic gear inside the transmission casing, which gear rotates in unison with the driven wheels of the vehicle. The pick-up device comprises a permanent magnet and a toroidal ferromagnetic core on which an inductive coil is wound. The permanent magnet and toroidal core are cooperatively arranged with respect to the ferromagnetic gear such that a magnetic circuit is created from the permanent magnet through the toroidal core, through the transmission casing, and through the ferromagnetic transmission gear back through the transmission casing to the permanent magnet. As the gear rotates, the reluctance of the magnetic circuit is varied at a rate representative of the speed of the gear and hence the speed of the vehicle. The speed information is provided across the inductive coil.

Abstract: A speed sensor circuit for providing a speed signal representative of the speed of a vehicle comprises a resonant tank circuit whose resonant frequency is modulated in accordance with the speed of the vehicle and a phase locked loop detector circuit which locks onto the frequency of the resonant tank circuit and provides a demodulated output signal representative of the vehicle speed.

Abstract: A fluid level sensor comprising a novel electronic circuit which monitors change in the fluid level in a reservoir through a conductive probe disposed therein. The probe and a capacitor are electrically connected in a circuit which is intermittently energized to create an electrical transient therein. The transient is monitored, and a warning is given when the transient indicates that the probe is not in contact with the fluid in the reservoir. Two embodiments are disclosed as applied to a vehicle hydraulic brake system having a dual reservoir type master brake cylinder with a probe for each reservoir. In one, only a single capacitor is required since the electronic circuit electrically connects each probe with the capacitor sequentially by means of time multiplexing. In the other, a capacitor is required for each probe and the transients in each capacitor/probe circuit are fed to a logic circuit which determines if any of the probes is out of contact with the fluid in the reservoir.

Abstract: A fluid level sensor comprising a novel electronic circuit which monitors change in the fluid level in a reservoir through a conductive probe disposed therein. The probe and a capacitor are electrically connected in a circuit which is intermittently energized to create an electrical transient therein. The transient is monitored, and a warning is given when the transient indicates that the probe is not in contact with the fluid in the reservoir. Two species of the invention are disclosed as applied to a vehicle hydraulic brake system having a dual reservoir type master brake cylinder with a probe for each reservoir. In one species, only a single capacitor is required since the electronic circuit electrically connects each probe with the capacitor sequentially by means of time multiplexing.

Abstract: Both visible and audible warning signals are provided for the purpose of promoting safety belt usage by the occupants of a vehicle. The warning signals are given for a limited time period subsequent to actuation of the usual ignition switch from the "off" position to either "start" or "run" position. If the driver fastens his safety belt prior to the expiration of the aforesaid time period, the audible alarm is terminated. Accuracy in the timing function is attained via an electronic control circuit.