Chime generator circuit for connection with existing automobile radio

Abstract

A chime generator circuit of the type employed to monitor the condition of parameters associated with an automobile, such as warning functions involving headlight operation, fastening of a seat belt, or indications of the ignition key having been inadvertently left in place as the driver is leaving the vehicle, etc. The circuit employs an oscillator which is modulated at a relatively low frequency, on the order of one or two cycles per second, and a unique coupling arrangement for exciting one of the existing speakers of the automobile radio to provide the necessary audible sound. In the disclosed device, the output of a signal generator is fed directly to one speaker, and a switch is interposed in the line extending between the radio output and the speaker. When the switch is open, the radio and speaker are isolated from one another and the generator feeds the speaker directly, producing the desired sound and warning the driver that a certain condition exists. A sensor and driver circuit receives a signal from the generator when the latter is operating, and controls the switch. The generator is enabled or disabled by one or more monitor switches that are disposed at various locations about the vehicle, and which open or close depending on the conditions being monitored. By the above arrangement, there is possible a significant cost reduction by elimination of the relatively expensive transducer heretofore associated with chime generators, since the present generator employs one of the existing speakers associated with the vehicle's radio.