Car Alarm Sound Booster
Friday, December 27, 2013
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For car alarms, emphasis should be put on hearing the audible alert and identifying it as belonging to your wheels. Unfortunately, modern car alarm systems seem to have more or less the same alarm sound especially if they are from the same brand. Also, to comply with legal noise restrictions, the alarm sound is not always loud enough to be heard if the car is parked down the road.
Simple Car Alarm Sound Booster Circuit Diagram
The circuit shown here is designed to help boost the alarm sound by also activating the cars horn(s) when the alarm goes off. lnternally the car alarm system often provides a signal that activates the (optional) engine immobilizer and/or volume (ultrasound) sensors. This signal usually goes Low upon sys-tem triggering and high again when the alarm system is deactivated.
The alarm activation signal is fed to the circuit through Dl . When in idle state, T1 s gate is High and consequently the FET conducts, keeping power FET T2 firmly switched off. When the system gets an active low signal, T1 switches off allowing timing capacitor C2 to charge via R2. About 15 seconds later, when the voltage across C2 is high enough, T2 starts to conduct and relay RE1 is energized. This, in turn, provides the required path for the lights flashing signal to energize RE2 and feed battery power to the cars horn(s).
When the alarm system is turned off the activation signal returns to High. T1 starts to conduct and rapidly discharges C2 via R3. T2 is then cut off and REl is de-energized. Diode D2 suppresses back EMF from REl. The circuit draws less than 2 mA when idling. When activated the circuits current consumption is virtually that of the RE1 coil. RE1 is any simple SPST or SPDT relay, capable of switching about 0.5 A (at 12 V). The coil rating is for 12 VDC and a current requirement as low as you can find. Fuse F1 should be a slow blow type and rated about twice RE1s coil current.
The B5.170 in position T2 can sink a continuous current of about 0.5 A. However, a value of 1.2 A pulsed is specified by Fairchild for their devices. To keep the FETs d-s current due to C2 discharging within safe limits, R2 may be increased, C2 decreased and R3 increased, all proportionally. A factor of 2 will keep the FET out of harms way with maybe a slight change in the 15-second delay and the sensitivity of the circuit. C1 is used as a smoothing capacitor and F2 should be rated in accordance with the horn(s) maximum current draw.
Caution. The installation and use of this circuit may be subject to legal restrictions in your country, state or area.
Source: http://www.ecircuitslab.com/2012/06/simple-car-alarm-sound-booster.html
high speed sound of jet engine, missile sound and machine gun sound. Each of these sounds can be activated by connecting the pins 12, 13, 14and 15 to ground by using the respective push button switches. Resistor R3 can be used for manually increasing or decreasing the speed.LED D1 gives a visible indication of the sound
