Relay for Car Alarm Siren Output

Hello guys. I have a problem here. I installed a Viper alarm on my VW bug, and I added a second siren (the very same model of the siren included on the package) back on the engine compartment just in case someone manages to cut the power wires of the siren on the front. When I got both sirens connected to the alarm siren output, it turned out that they both only sound when the alarm is triggered, but the arm/disarm chirps don't work. Chirps work only with 1 siren hooked up to the alarm siren output. I tested the alarm output with a multimeter and it barely shows about 1.5 to 2 volts when sending chirps, and 12v when sending a continuous signal for the siren. Given this fact, I got a relay to see if I could drive it with the alarm siren output, but that didn't work either, so I figured that I needed to juice up that siren alarm output in order to drive that relay, let's say maybe a transistor or something to boost those 2volts up to 12v to make the relay coil to close the circuit. I want you guys to tell me if I can only just throw a transistor in there (along with some resistors, maybe) connected as follows: 2v Siren alarm output connected to the transistor's Base 12v from battery connected to transistor's collector 12v to coil pin on relay connected to transistor's emitter Sorry for not including a schematic, but I think my description is clear. thanks in advance.

I have the same setup both in the engine compartment, but I wired both the + , - to the alarm & Alarm ground and it works fine. Could be the length of wire is causeing to much voltage drop due to resistence. The only way that I know to make both work when having your problem is to try using a capacitor on the Alarm siren output.

lurch228 wrote: I have the same setup both in the engine compartment, but I wired both the + , - to the alarm & Alarm ground and it works fine. Could be the length of wire is causeing to much voltage drop due to resistence. The only way that I know to make both work when having your problem is to try using a capacitor on the Alarm siren output.

Yeah, I figured what you said, and that's why I tested the voltage the alarm sends when sending chirps, reading out just about 2 volts or less. That's why I got the idea of using a transistor so I can switch a positive 12v wire to the coil of the relay using the alarm output.

Or look in digikey etc. for a 2 volt coil relay if such a beast exists.

Alternative: If your Viper has it use the horn output (BROWN / white -) to trigger a relay for the second siren, that will retain your chirps on the first siren.

vwgenerallee98 wrote: lurch228 wrote: I have the same setup both in the engine compartment, but I wired both the + , - to the alarm & Alarm ground and it works fine. Could be the length of wire is causeing to much voltage drop due to resistence. The only way that I know to make both work when having your problem is to try using a capacitor on the Alarm siren output. Yeah, I figured what you said, and that's why I tested the voltage the alarm sends when sending chirps, reading out just about 2 volts or less. That's why I got the idea of using a transistor so I can switch a positive 12v wire to the coil of the relay using the alarm output.

Never played with transistors so maybe someone else can help with that, but the siren will only trigger the chirps below a set voltage. So I thought a small cap would stiffen the volt output just enuff to make both sirens chirp, but it will also shorten the pulse of the 2 volts, so size of cap might matter, ie to big of cap to short of pulse, if the siren has a set minimum pulse to activate. So trial and error for the right cap. If your transistor idea is to use one that has some kind of delay or minimum voltage to activate it should work. but feeding the 2nd siren a 12 volt source even through a relay will trigger full siren if the 2 volt activates the relay with out a resistor to reduce the 2 volt to low enuff input to not activate the relay and still achieve enuff of the 12 volt through for full siren. I've never tried either so I may be wrong but it cant hurt to give it a try.

The dual sirens that I have connect are 514t sirens the larger versions of the 514n.I did some testing with the only spare 514n siren I have and a 5v supply, I believe the chirps are a low voltage pulse into the siren connected to a capacitor in the siren. I think the wire loop is wired to capacitor which asorbs voltage for the soft chirp, then when fully charged you get full volume. I think you can cut the wire to see if the chirp works. If the loop is cut to make the chirp louder it will pass more voltage through to the siren when not charging the cap. When using the 5 volt power it dosen't charge as quickly and you can tell the difference in volume as it is using quieter part of the begining of the first tone for soft chirp. If I'm right then cutting the loops on the siren's will stop the caps from absorbing voltage as the won't be connected. Even when connected to a 5v power supply the siren still goes to full alarm after the quieter chirp with constant power just at a lower volume. If you try it and it works please post back.

lurch228 wrote: The dual sirens that I have connect are 514t sirens the larger versions of the 514n.I did some testing with the only spare 514n siren I have and a 5v supply, I believe the chirps are a low voltage pulse into the siren connected to a capacitor in the siren. I think the wire loop is wired to capacitor which asorbs voltage for the soft chirp, then when fully charged you get full volume. I think you can cut the wire to see if the chirp works. If the loop is cut to make the chirp louder it will pass more voltage through to the siren when not charging the cap. When using the 5 volt power it dosen't charge as quickly and you can tell the difference in volume as it is using quieter part of the begining of the first tone for soft chirp. If I'm right then cutting the loops on the siren's will stop the caps from absorbing voltage as the won't be connected. Even when connected to a 5v power supply the siren still goes to full alarm after the quieter chirp with constant power just at a lower volume. If you try it and it works please post back.

Thank you so much for your reply, lurch. Actually I figured that out in the first place. I'm not so literate with electronics (especially with capacitors, I'm still working on them) but I figured that the wire for the soft chirps would be causing the problem. I cut the wire on 1 siren then on the second one and I still had the same no-chirp problem. The alarm I've got is the 500HF and it's got no extra horn honk wire,so I can't count on that. But what calls my attention is that the instruction manual says that I can drive the factory horn with the siren wire if I put a relay, but I can't manage to turn the relay on with the chirps either. Anyway, if I can't make both sirens to chirp, I would like at least 1 to chirp and then both sound off when the alarm is triggered.

That the same as mine I have 2 550hf but only one has the dual sirens. If you already tried those then the only other thing is the bjt npn transistor to boost the voltage I know it can be done in priciple but don't know how to calculate the resistor(s) needed to get the voltage up. I know that you connect the 12vcc too the collector and the siren output to the sirens to the emitter, and the siren from the alarm to base. But to get the voltage up from the 2 volt thats where I get lost.

lurch228 wrote: That the same as mine I have 2 550hf but only one has the dual sirens. If you already tried those then the only other thing is the bjt npn transistor to boost the voltage I know it can be done in priciple but don't know how to calculate the resistor(s) needed to get the voltage up. I know that you connect the 12vcc too the collector and the siren output to the sirens to the emitter, and the siren from the alarm to base. But to get the voltage up from the 2 volt thats where I get lost.

Well that's the thing I want to figure too. I know an NPN transistor acts like a valve, you put voltage on the base and the 12v will flow from the collector to the emitter. I don't know if whether any resistors are needed (maybe the transistor supports the 12vcc) and if it will work as I'm assuming. I was also thinking that maybe I don't need the relay at all, just the transistor. So basically what I need is to know the appropriate transistor and if there's anything else I need to hook up to it.