Apparatus for detecting a start of an engine for a motor vehicle

An apparatus for warning of a start and stop of an engine starter motor energized through a wire from a battery in a motor vehicle, comprising:

• sensor means including a coil detachably disposed around said wire for sensing variations in a magnetic flux generated around said wire when a direct current for driving said starter motor starts flowing and subsequently stops flowing from said battery through said wire to said starter motor and for outputting voltage signals corresponding to said variations in magnetic flux;
• and
• judging means for comparing said voltage signals outputted from said sensor means with a reference voltage signal and for outputting detecting signals which indicate respectively that said starter motor is started and stopped when said voltage signals exceed said reference voltage signal by a predetermined amount, said judging means comprising an amplifier for amplifying said voltage signals, a comparator for comparing each amplified voltage signal with said reference voltage signal to generate a pulse signal when an amplified voltage signal exceeds said reference voltage signal by said predetermined amount, a monostable multivibrator responsive to said pulse signal from said comparator to generate said detecting signals to provide an indication of starting and stopping of said starter motor;
• and
• warning means for warning of said start of the engine in response to the one of said respective detecting signals from said judging means indicating that said starter motor is started.