trigger when negative is lost

Hello,
I am a newbie here. I have a question regarding relay setup. I've looked over the relays menu of the site and did not find my answer (perhaps I was looking at the wrong place?). I was hoping someone here could give me a quick hint. Thanks.

Question is simple, I have a Device A sending negative (-) signal to Device B under  ALL conditions, except when I press the keyless remote which is the moment I want to trigger Device C with 12V+. I haven't tired it yet, but would the diagram below work? It seems to me that coil between 86/85 is energized most of the time except when 85 loses negative signal, and when that happen, Device C gets triggered. Is that correct?

If that is correct, because 86/85 is energized most of the time, if I leave my car in the garage for like 2 weeks, would this design drain my battery? Is there another way to trigger C, when A stop sending negative signal to B?

Thanks for answering my questions. :)

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Dennis da Newbie

where is the trigger from the alarm?

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This is a new simple alarm system I get here in Taiwan that does not come with remote/receiver but rather work ONLY WITH factory keyless system. My car is a 1999 Honda Prelude which came with keyless remote with no alarm. I had a Clifford alarm for years until it recently died on me. While I had the Clifford alarm, I put aside the factory keyless remotes because Clifford alarm came with 2 remotes that arm the alarm and lock the doors. Now that the Clifford alarm is removed from the car, I am now back with factory keyless remote.

Well, I didn't explain the entire story because I didn't and still don't know how to explain it without complicating it, and really it is just a simple question. But ok I'll give it a try. As I mentioned, the simple alarm I get here doesn't come with remotes nor have a receiver in the alarm base unit. But other than that, there really is no difference between it and any other regular car alarms.

Since it doesn't come with remote, in order turn on/off the alarm, there are 3 wires required (2 of them need to be triggered at the same time). wire#1 and wire#2 are connected to Door Motor(lock) and Door Motor(unlock) and can be set to positive or negative input (by the jumper), the 3rd wire is in fact the wire that I was asking in my first post above (the blue wire in my diagram). It needs a positive input at the same time when wire#1 or wire#2 is triggered.

Now, for some of the cars that come with factory keyless remotes, when it is to lock/unlock the doors, the turn signal lights also come on momentary. If that's the case, it makes it easy because all I need to do is to connect the blue wire (first post above) to it. So when keyless remote is pressed, the door is lock/unlocked, the door motor triggers wire#1 or wire#2, and the turn signal triggers the 3rd blue wire (first post above). Alarm is not turned on or off. Unfortunately, my keyless remote doesn't do anything except to lock or unlock the doors. So I had to figure out another way to trigger the 3rd wire (blue wire in the first post above).

To the diagram I have in the first post:

Device A: Factory Keyless Receiver
Device B: Multiplexer
Device C: Alarm

There are total two wires (black wire shown in first post is one of them) connected between Device A(Keyless Receiver) and Device B(Multiplexer) and both wires have constant negative signal under all condition. I am counting on that when I press the keyless remote, at least one of the wires will drop the negative signal so I can use the relay set up I drew above to get the 3rd wire (blue) to trigger the alarm.

A simple question that sounds complicated, isn't it? Any suggestion is appreciated.

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Dennis da Newbie

If the keyless receiver just passes on an RF signal to the multiplexer, you probably won't be able to use either of those 2 wires to activate anything.  Have you metered them to see what they show when the remote is used?

I'm still slightly confused as to what wire #3 is supposed to connect to - it would be helpful if you could post exactly what the instructions say about it, but I'm assuming it is supposed to go to whatever wires come on with keyless entry so that the alarm knows that the remote is being used and not just the lock switch.

So you said your factory keyless does not flash any lights when the remote is used, correct?

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C Renner's Auto Electronix
My service is cheap, quick, and good - pick any two

When your ground from A goes away, what voltage does the signal at B go up to? Is it 12V or 5V?

It looks like the sense of the signals is the same, meaning that when the input is low you want the output to be low, and when it's high, the output should go high.
I assume you can't just connect them together because of drive or loading requirements, so you could use some solid state components to act as a driver stage. You have to get more information about the signal levels and details such as source and input impedances to see what you can use.
The relays setup you show might work, but that'd definitely drain down the battery in short order; you can't use a setup where you have relays energized in a standby configuration without powering it from an outlet.

chriswallace187 wrote:

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... but I'm assuming it is supposed to go to whatever wires come on with keyless entry so that the alarm knows that the remote is being used and not just the lock switch.

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Yes, that's exactly the idea, otherwise the alarm may be turned on/off with lock switch which would be stupid.

dualsport wrote:

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... The relays setup you show might work, but that'd definitely drain down the battery in short order; you can't use a setup where you have relays energized in a standby configuration without powering it from an outlet.

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It's what I thought too, which is why I thought I should ask the experts first.

Luckily, my problem is now solved. When I first post my question here, I didn't really probe the wires because I was at the office not doing any work but studying my car's service manual. The manual stated that the two wires between keyless receiver and multiplexer both have constant negative signal under all conditions and when probing them to ground, I should always get battery voltage. The manual was wrong, I tried probing it today, one wire sent out negative only when I used the remote to lock the door, and the other wire sent out negative signal when unlock with the remote.

So it's all set, I can just use these two wires to trigger my alarm's wire#1 and wire#2 instead of door motors, and as for the 3rd wire that requires positive signal, I'll just connect to a fused (+) or I can try using the Relays diagram from the web site to convert polarity then send it to the 3rd wire. Either way will distinguish the remote trigger from just been lock/unlock with the lock switch.

Thank you all for your help. This is a great site with friendly environment and a lot of useful info. I'll definitely be coming back regularly.

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Dennis da Newbie