I need a circuit that will detect the failure of a 12 volt bulb on a car. Not only one bulb but all the road lights are to be monitored.

Can you assist please?

 

Why not monitor the current going to each light? You could use a shunt or very low value resistor, and measure the voltage drop across it. I used to have a car where there were fiber optics near each lamp and the other end was visible from the driver's seat, either directly or in the rear view mirror, so it was always easy to see if you had a lamp burnt out. Perhaps you could use a phototransistor to sense the actual light from each lamp.

 

There are a few IC's on the market specifically designed for this task, check out the 'automotive IC's' section of suppliers such as ST and National. Typicaly such IC's are able to monitor the circuit current of several circuits.

Alternatively you can pilot the lamps with intelligent MOS devices which have built in load fault detection abilities.

 

If you put a relay for example 5 volt relay
series in bulb circuit when you turn on the lamp
if your lamp is ok current will flow trouth the relay and lamp then teh relay will be active
if the lamp is not ok the relay will be off too
bye

 

Lamp current could be monitored via a reed relay. The magnetic force needed to activate the reed can be provided by some faily large size wire (thereby having loss insertion loss) wrapped around the reed. The number of turns is dependant on the sensitivity of the reeds you buy and the amount of current you need to run the lamp. Use just enough turns to activate the reed contact when the lamp is operational (with a margin of safety). Monitor the reed contacts for activation and if the lamp fails... the reed drops out !
This technique is currently in use on locomotives to monitor headlamps and class lights.....beats having to get out, walk around and look!

Gerald Beaudoin

 

Spraque had a ULN series of IC's specifically for Automotive Lamp
Failure detection.

Regards,
Phil Corso, PE
Boca Raton, FL
[[email protected]] ([email protected]) {[email protected]}

 

The quickest, easiest, cheapest way, that I can think of, is to affix a Cadium Sulfide (photocel) to the lamp to be monitored. Their resistance drops dramatically, when they see light. Then simply monitor the outputs of these cels to know the condition of the lamps that they ajoin. -MIKEM

 

Gerald Beaudoin has the good idea. Find a reed with about a 15 -20 AT. That is pretty low pull in. Also - if your going through a relay use a diode as a snubber circuit.

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Measure the current.

 

My two cents... Drive the lamp with a smart driver. The driver will report back an error of a fault in the load. Example: Motorola MC33298 driver. This is used for driving resistive or inductive loads and reports a short or open load.

Jack

Jack Eskew
Microsmith, Inc.
301 W. Deer Valley Road # 3
Phoenix, AZ 85027
V: 623-587-6473
F: 623-587-0612
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