alarm to a car horn

Here is my problem. As you can see on the diagram I made, I connected the alarm to a car horn, the problem is that when you enable or disable the door locks the input are just three pulses. I can hear the three pulses activating the relay three times but the problem is when it reaches the flasher. As you can see the three pulses become just one very low pulse which I can barely hear. I don’t mind it being just one pulse, but I would like to hear it louder so I can know if I really locked my car.On the other hand when the alarm is active the input is one long pulse until it is deactivated. The output works perfect they are long and loud pulses as they should be.What can I do about that small pulse? Any ideas?

From the diagram it looks like you have (+) door lock output to the relay , is this correct ? If not, what you can do is wire in a relay to go directly to the horn from the door locks output of the alarm system. This will bypass the flasher and you will be able to use the output of the door trigger's to go directly to the horn.Jeff

Velocity Custom Home Theater

Mobile Audio/Video Specialist

Morden, Manitoba CANADA

BTW, you will need to use diodes to isolate the trigger's.Jeff

Velocity Custom Home Theater

Mobile Audio/Video Specialist

Morden, Manitoba CANADA

The problem is that with this alarm, when you start the car the locks close automatically and when you turn off the car they open automatically. So my guess is that if I wire a relay from the door locks to the horn it will beep every time I start or turn off the car. Any ideas? Here is the diagram of the alarm, due to the size restriction I hope its visible.

You can add a pulse stretcher circuit using monostable, or a mosfet and a few discrete components, so the relay will stay on for a half second or so when the alarm pulses. Either that or you could just add an extra electronic siren that'll respond quick enough for you to hear the short chirps.

Sorry for my ignorance but how can I make a pulse stretcher circuit, do you have any schematic? Thanx for the idea

I don't have an easy way to draw up schematics as nicely as you have there, but maybe I could describe it- Using something like a 2N7000 MOSFET or equivalent (I bought a bag of 100 from mouser.com for 8 cents each) 2N7000 This is a very high input impedance transistor, so it draws no current from the trigger signal. Connect your alarm siren output signal to the gate of the transistor through a diode, forward biased, so it passes current when the signal goes high. Connect a resistor and capacitor in parallel, and put one side of the leads to ground, and the other side to the transistor. What this does is allow the cap to charge up quickly through the diode when your signal comes on, and then when it shuts off again, discharges slowly through the resistor. If you pick a large resistor, the transistor will stay on for a longer time. The source of the transistor is connected to the coil of a relay, and the drain to ground (relay set up for ground trigger actuation, with constant 12V on the other side of the coil). I'd add another diode across the source and drain of the transistor for added protection from the relay coil kickback when it switches off, especially if you happen to be using a large relay, since they can produce a large voltage spike when turning off. You can experiment with the values of resistor and capacitor to give you the desired time needed for the arming pulse, since your flasher may add a delay before sending the power to the horn. Rough timing should be about resistor x capacitor values, so you could start with a 10uF cap and 100k resistor for an output of about a second, and change them as necessary. A larger cap will increase the pulse duration, as well as a larger resistor. Try to avoid static when handling the transistor before everything is hooked up, since it's sensitive to ESD, electrostatic discharge. For 8 cents a piece though, <shrug>..

Oops, wrote it backwards in the description there; the source (S) should go to ground, and the drain (D) of the transistor goes to the relay coil, not the way I described up there. Here's the datasheet for the transistor, which shows which leg is which on the transistor. Might be good to use a potentiometer as a resistor, so you can tweak the thing as needed, in case you want a longer or shorter pulse.