I once did in my electronic classes a small circuit that acted like a slow rise circuit. Example: If this circuit would be installed with a siren, it would make the siren start not loud and get louder after couple seconds.
I'm asking cause my car alarm doesn't have a silent arming/disarming function and i'd like the siren to make less noise upon arming/disarming the system. (I'm waking the neighboors when I go out at night). With this circuit, the arm/disarm chirps could be less loud so I don't wake anyone, but if the alarm goes off, the siren would be full blast after maybe 1-2 seconds. .. I know this circuit exist, I just can't find it.
ok install a stop light bulb in series with your alarm horn it should reduce it to a meow..short out the bulb with a relay and presto back to normal..happy now ?
First thing that comes to mind is a simple RC circuit driving the base of an NPN transistor - i'd imagine the radioshack TIP-3055 to be a cheap effective answer.
It seems to me you'd want to seperate one lead of the siren from ground and reconnect that to your collector then tie the emitter to ground with the RC giving the slow rise signal to your 3055's base.
RC signal slowly goes high, transistor slowly begins to pull the collector low (ground leg of siren here remember) thereby slowly increasing voltage difference between the siren terminals from say 12v/11v eventually down to 12v/0v .
This is of course assumes a pretty much linear relationship between volume and voltage, if you hook up the siren to a variable resistor and find a sudden logarithmic jump from silent to full blast, you'll have to to a little RC tweaking/biasing to slow down that ramp up time.
Slow rise circuit (siren related)
Posted - Jul 04 2005 : 2:42:51 PM
