HeadLight Warning System

**owenjh** · 07-27-2004, 12:14 PM

Hey, just wanted to know how I would go about getting a warning whenever I leave my headlights on. Since I replaced my stock head unit. I have left them on twice by mistake now. I know it can be done, but was just wondering how, maybe I could interface thru the parrallel port or something? or, I could even have it cut the power to my lights when windows shuts down, and cut them back on when windows restarts. Just trying to get ideas while im stuck at work for another 8 hours. Please leave any ideas / comments

**yes I am an idiot.

**brandon** · 07-27-2004, 12:21 PM

Your headunit was linked to your lights-on-signal-warning? I've never encountered that before.
Back when I was in highschool I purchased a 1976 AMC Gremlin that had been stripped, gutted, and raped. I had to redo the entire electrical system and came up with an awesome idea. Why not link my headlights to my ACC, that way when I started my car, my headlights would come on and when I turned my car off they would go off. I even hooked up a kill switch to it so that I could manually turn them off. This was before any of the Big 3 came out with automatic headlights or daytime runners.
Maybe you could do something like that? The only problem is that you would have to turn your key to ACC in order to have them on while the car is not running.
Or maybe you could rig up a relay to turn them off 60 seconds after the ignition is turned off.

**crisr** · 07-27-2004, 01:24 PM

You could do it with a relay and a buzzer:

Code:

       relay coil
acc --/\/\/\/\/\/\--- gnd
    -----.   .----.-------- headlight wire
       NO ./  NC
           |_______ buzzer ___ gnd

I just don't know why would you interface it to the carputer? Do you leave it on when you leave the car??? And just imagine windows crashing and the headlights turning off at 65mph at night!!!

**owenjh** · 07-27-2004, 01:35 PM

Originally Posted by crisr

I just don't know why would you interface it to the carputer? Do you leave it on when you leave the car??? And just imagine windows crashing and the headlights turning off at 65mph at night!!!

- Maybe not such a good idea then, but I do have DRL's

Car was OBD-II so the signal got sent from the bus to the head unit, when the head unit recieved that signal it chimed.

So really I just want a chime so that I can turn them off if they are on... wonder how I could do that

**god_of_cpu** · 07-27-2004, 02:08 PM

The OBD-II protocol is only used for diagnostics not for carrying data between different systems within the car. If your car is newer it probably uses a CAN-Bus or some variant thereof to carry the data. To read something off the bus would be a complicated and expensive thing to do, assuming you can even back engineer the protocol used or find information on it. Your best bet would be to just tap into the signal line that gets switched on and tie this into a serial or parallel port as well as the ignition line then just write a program that reads this and generates an audible aleart.

See this link for interfacing with the serial port, should be similar to what you need to do, just play a sound though instead of shutting down the computer.
serial port shutdown signal

**crisr** · 07-27-2004, 02:14 PM

Originally Posted by owenjh

- Maybe not such a good idea then, but I do have DRL's

Car was OBD-II so the signal got sent from the bus to the head unit, when the head unit recieved that signal it chimed.

So really I just want a chime so that I can turn them off if they are on... wonder how I could do that

As I said, you can just use a relay and a buzzer (anything that makes a noise when connected to 12VDC), as in the diagram - use the relay's Normally Closed (NC) contacts.

**owenjh** · 07-27-2004, 03:48 PM

Originally Posted by god_of_cpu

The OBD-II protocol is only used for diagnostics not for carrying data between different systems within the car.

Ok ok, it may not be part of OBD-II but the haynes manual for my car tells me at what frequency a signal is sent to my stereo to make beeps, and what for and all of that stuff, Should not have said OBD, they sell wiring harnesses where you put the head unit in the trunk for close to $80 but thats alot of money for a ghetto solution.

**owenjh** · 07-27-2004, 03:50 PM

Originally Posted by crisr

As I said, you can just use a relay and a buzzer (anything that makes a noise when connected to 12VDC), as in the diagram - use the relay's Normally Closed (NC) contacts.

I surely can't do that because then the buzzer will be on all the time my lights are on when im in the car.

**god_of_cpu** · 07-27-2004, 03:53 PM

Originally Posted by owenjh

I surely can't do that because then the buzzer will be on all the time my lights are on when im in the car.

Just tie a relay into the the cars ACC line that will switch off the buzzer when the car is on.

**crisr** · 07-27-2004, 05:04 PM

Exactly, that's in the diagram I "drew" on my first reply.

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