Simple Car Alarm Arming Horn Beep Canceller


It's a great convenience that most modern cars come with a built in alarm, however it is nothing but noise pollution that the horn sounds when the alarm is armed. Disconnecting the alarm system from the horn relay will eliminate this, but prevent the horn from sounding in the even of an actual alarm. This circuit serves to silence the arming beep yet maintain the alarm by introducing a small delay into the signal. It sits between the alarm and horn relay. The alarm must provide a constant horn signal for at least 3 seconds before the horn relay is activated. That way the quick "beep" will never activate the horn relay, while the constant alarm signal will. 


Simple Car Alarm Arming Horn Beep Canceller
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Part
Total Qty.
Description
Substitutions
C110.01uF Ceramic Disc Capacitor
C21100uF 35V Electrolytic Capacitor
R111K 1/4W Resistor
R2110K 1/4W Resistor
R3115K 1/4W Resistor
R41470 Ohm 1/4W Resistor
D1, D3, D431N4004 Rectifier Diode
D21Red LED
U11555 Timer IC
K11SPST 12V Automotive Relay
MISC1Board, Wire, Socket For U1, Case