Car alarm central locking button

[BioniC187]

Hey okes, the alarm system in my car is not so great. The central locking only works if i activate it from the transmitter.
Let me explain better with this.
Example:
If car is off - press "arm" button - the alarm activates itself including the central locking.
If car is on - press "arm" button - the central locking only activates itself.

So thats the issue, if i am sitting in the car waiting for someone, i would like to be able to lock my doors without the alarm coming on. Or another example, if i am getting in my car late at night, as soon as i get in i would like to be able to lock the doors to be safe, as it stands i have to start the car and then only i am able to lock the doors.

So i would like to somehow isolate the part of my alarm that sends the signal to the central locking acutators, and have a lock and unlock button somewhere that will not activate the alarm and only the central locking. Has anyone done this before?

Thanks

 

[alec_t]

The alarm and locking systems vary from one car manufacturer to another and from one car model to another. You need to specify an exact make/model/year to have any hope of getting a useful answer. Even then, there may be no member here with knowledge of the relevant system

 

[KeepItSimpleStupid]

It sounds like the locking system was added with a non-OEM alarm.

If you had factory door locks, you would have a lock/unlock button at the passenger and driver's doors which would do what you need to do.

Usually the alarm has a Lock/unlock pulse with an external relay for lock and unlock. Paralleling an (ON)-none-(ON) switch across essentially the alarm transistor output, gets you what you want.

I did something unusual when I put an alarm in one of my cars. One switch I added was Valet and the other disabled the passenger door unlock command. This was basically so if I was alone, the passenger door would not unlock. Some alarms use a double press to unlock both doors.
I added the door lock actuators as well.

In a smart alarm system, Key presence is used to disable the lock relays and that's what you want. I know the hard way. I didn't initially connect the key presence to the alarm system. There was a nearby tornado and lightning strike that caused my doors to lock with the keys in the ignition, raining and the car running. Not good.

Now, my current car is somewhat smart. If the doors are locked using the lock push button and the key is in the ignition and the door is open, the locks automatically unlock.

I sometimes carry two keys so I can keep the car running with the doors locked while I'm outside the car in the winter.

The system disables the keychain lock/unlock if the car is running, I believe. I don't use the remote.

 

[BioniC187]

Hmmm, I opened up the alarm unit, and there are 3 relays. So i am guessing that 2 of the 3 are for lock and unlock. All 3 relays are 4 pin relays.
Essentially all the central locking actuators are connected on one power rail, so i can open it up, and check for continuity to find the both the relays, as it would connected to 2 of them.
Now like you said, the unlock pulse, this is gonna be an analogue signal since its relays. So at its most basic, say i have lock unlock switch, that sends say 3V to each relay to lock and unlock?
I don't want this signal to end up affecting and or damaging the alarm system

 

[KeepItSimpleStupid]

A pulse is basically a digital signal. ON for a given amount of time.

Typical Relay functions could be: lock, unlock, starter disable, light flash, trunk unlock

Two pins should basically be accessible to the user. So these relays could be SPST, so there will be 2 terminals for the contact and 2 for the coil.

These relays: **broken link removed** or "Bosch automotive relays" are very common for alarm installs.

You may have to use one or two especially if you want to use a low current easily hideable switch for lock or unlock.

Take a piece of hose and listen to the relay (act like a stethescope) when the lock and unlock pulses are sent to identify.

Depending on the vehicle, it may use a contact to ground or a contact to positive. Way back when (60's) Ford switched the positive for the dome lamp and Chevrolet and Chrysler switched the negative. Don't assume.

In this case, your going to want to parallel a set of contacts across one of the existing relays. The current draw of a lock system may be unknown. Very old cars used large solenoids. Now, the way to do it is to use a motor that drives a rack and pinion.

In order to have a "small switch" activate a "large load", you probably should use an Automotive relay to get that 30A rated contact.

Relays can have terminals labeled NO for Normally Open, NC for Normally Closed and C for common. The NO position is where the Common contact and the NO contact are not connected when power is off.

You can also place a voltmeter ACROSS the relay contact. When the relay isn't energised, you will see 12 V. It will blip to zero when it pulses.

This kind of use of a voltmeter might confuse you, but the circuit would consist of the battery + terminal, load, the relay and ground. Since you meater draws very little currrent to measure voltage, the actuator looks like a wire with the relay being the open in the circuit. Measuring across the relay will show 12v. When the relay is activated, the leads of the voltmeter see nearly 0 resistance with a large current and thus reads zero to a few mV of voltage.

Voltage measurement from ground to the relay contacts and also from + to the relay contacts can help you figure out what side is switched.

 

[BioniC187]

Something went wrong with the alarm today, getting the installer to fix it, so i'll ask them about it aswell