Building a home-made circuit for monitoring car lamps

[jumpjack]

Most expensive cars have a built-in "lamps-checker" which warns you if anyone of the lamp burns out.
Is it possibile to build an hand-made circuit which accomplish same task? At which costs?

 

[pakitos]

Monitoring car lamps

there are several ways to check that.
the cost for sure is dependent on the way
do you know electronics?

 

[jumpjack]

Re: Monitoring car lamps

there are several ways to check that.
the cost for sure is dependent on the way
do you know electronics?

not enough to "decode" an unknown complex schematic, but I have some basic knowledge of analog electronics; I also successfully built a PIC-based circuit, programming it by myself (but I used a ready-made programmer...).

The simplest thing I can think of to solve this issue is light-sensitive resistor per each lamp connnected to a proper circuit... but it does not look so smart, I'm sure a better method should be available!

 

[rikie_rizza]

Monitoring car lamps

Oh come on, if the car use a bulb, it means that you can measure the resistance. when it burns out, there will be high resistance...a.k.a no voltage! No sensor needed, just high voltage logic.

 

[jumpjack]

Re: Monitoring car lamps

Oh come on, if the car use a bulb, it means that you can measure the resistance. when it burns out, there will be high resistance...a.k.a no voltage! No sensor needed, just high voltage logic.

it looks simple...
Unfortunately, I can READ schematics, but can't CREATE them... so I was asking for help...

Anyway, it LOOKS simple, but I think it is not:
lamp is ok --> switch is on/ switch is off --> lamp on / lamp off
lamp is broken --> switch is on / switch is off --> lamp always off

How do you distinguish among these 4 cases?!?

B,S,L (Burnt out, Switch, Lamp):
n, on, on
n, off, off
y, on, off
y, off, off

 

[KMoffett]

Re: Monitoring car lamps

I thought that was the way to go too until I drew up a schematic. The problem is many of the lamps are in parallel, so the 12v end of a burned out lamp still has a low resistance path to ground through other lamps.

Ken

 

[laktronics]

Re: Monitoring car lamps

Hi,
Your first idea is better, since it is contact less solution. It can show the on status of various lamps using an LED display on the console so that the driver can see if any lamp which is expected to glow, is not glowing.
Direct connection to the lamp circuit is not advisable for a user to do and I do not think it gives more useful information.
Regards,
Laktronics

 

[KMoffett]

Re: Monitoring car lamps

It would be tough to mount all of the LDR's so they had views of the bulbs in all those different housings, and not be affected by other outside lights.

I saw an article in an electronics magazine many years ago where they had taken several turns of the wire leading to each lamp and wrapped them around a small reed switches. With the lamp ON, the high current created a magnetic field that closed the reed. If the lamp was OPEN there was no current and the reed stayed open. I never tried it, and it would probably require cutting into some of the wires for enough wire to make the coil. In fact I think they actually did that.

The magnet field idea makes me wonder if you could place small Hall-Effect senors against wires and get an output change. ???? Single wires running to parallel lamps would still be a problem, unless the sensor could detect the difference between full and half current with one lamp out.

Food for thought.

Ken

 

[jumpjack]

Monitoring car lamps

I just discovered hall transducers.

How can I know if a hall transducer is sensitive enough for this application?

 

[KMoffett]

Re: Monitoring car lamps

Like I'm going to do (today)...order some and try them.

Ken

 

[shwoo]

Re: Monitoring car lamps

There are some dedicated IC to do the job.
TEMIC, now ATMEL, makes some.
Please refer to the data sheet attached.
They have one more part number doing similar jobs.

S. H.

 

[KMoffett]

Re: Monitoring car lamps

They didn't say it specifically in the datasheet, but is the Rs the resistance of the wire between the switch and the lamp?

Ken

 

[shwoo]

Re: Monitoring car lamps

Well, the whole purpose is to sense the health of the lamp remotely.
In other words, we usually don't want to put an extra wire to the lamp.
If you put extra wire, you can put photo sensor or you can measure voltage
drop of the main wire.
Rs should be a very small sense resistor to minimize voltage drop.
I don't like TEMIC style datasheet, as they give minimum information
and I feel like I am a kit builder rather than a designer.
S. H.