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car bulbs failure detection

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jumpjack

New Member
I'd like to build a circuit to detect when any of my car light fails
I bought a pic 16f877 as I thought I could use its A/D converter to get a simpler circuit just needing proper interfaces among the lights and the A/D converter input.... but now it looks like it's not so trivial. :(

Any help?
 

tcmtech

Banned
Most Helpful Member
I usualy just walk around may car now and then after dark with all the lights turned on.
(But thats a just me) :D
 

Boncuk

New Member
Connect a very low value resistor (10mΩ) in series with the bulb and sense the voltage drop across that resistor which will go into a comparator.

If the bulb is OK there will be a voltage drop according to bulb power. If the bulb is defective the voltage drop will be zero (on the low side) and full battery voltage if placed at the high side.

Boncuk
 

picasm

Member
If you are concerned about car bulb failures why not just replace them with LED versions instead?
 

Boncuk

New Member
If you are concerned about car bulb failures why not just replace them with LED versions instead?
How many LEDs would he need instead of a 55W high beam bulb?
 

Sceadwian

Banned
I ran out of fingers.
 

Sceadwian

Banned
I got to 1500 leds, then my fingers knotted permanently, it took me 4 hours to write this response =)
 

Externet

Active Member
I'd like to build a circuit to detect when any of my car light fails...
Any help?
A photocell/phototransistor by the bulb location can send a signal to a circuit for detection if you want an electrical solution.
Unless you want to do it as Cadillacs, with optic fibers from the bulbs locations to a central sensing/indicator circuit at the instrument panel.

Seen simple fiber ends by the bulbs ducting a glow to the instrument panel too, no circuitry. What could be better ?
 

colin55

Well-Known Member
Buses need to detect when a globe fails.
The circuit I designed consisted of a few turns of thick wire around a reed switch and a plug and socket on each end. The unit was fitted to each lamp to be monitored and the reed switches were connected in series to a buzzer. When anything failed the buzzer sounded.
I sold thousands of the units. Nothing else came as cheap or reliable as this design.
 

Boncuk

New Member
Buses need to detect when a globe fails.
The circuit I designed consisted of a few turns of thick wire around a reed switch and a plug and socket on each end. The unit was fitted to each lamp to be monitored and the reed switches were connected in series to a buzzer. When anything failed the buzzer sounded.
I sold thousands of the units. Nothing else came as cheap or reliable as this design.
Sounds good.

How many turns did you apply to monitor a rear light of 4W?
 

colin55

Well-Known Member
The lowest wattage for a bus was 18watt. This required 5 - 6 turns, but you can use much thinner hook-up flex and cover the reed switch with 20 turns or more if needed.
 

duffy

Well-Known Member
All's fine until you get to the alternator bulb. That one's weird. Current flow is bidirectional, and it is used to provide initial field current to the alternator. It's the one you would MOST want to check, and the one that's the hardest to do so.
 
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