Bulb sensor

[yonubear]

Hey dumb question I am trying to make a sensor like a car uses that indicates a blown bulb. Any part suggestions?

Thanks,
Yonu

[scotty101]

An Operational Amplifier setup to monitor current through the circuit to the bulb. No current and switch on = blown bulb.

[yonubear]

Thanks now to hunt up an example

[grahamed]

Hi

Buy a naked read switch - like http://www.ebay.co.uk/itm/10X-Functiona ... 462b9b488d

Wind several turns of solid core wire round it to form a coil - enameled wire is best - how many turns depends on the current the bulb should take - pass the bulb current through coil.

Did this on my mini back in 1970 to detect brake light failure.......for some reason PC Plod liked to stop me for a roadside MOT if he could see any excuse. I didn't need a Pi.

[grahamed]

Hi

If you want an electronic version.

bulb sensor.jpg (16.91 KiB) Viewed 885 times

Output is low when lamp draws current.

R2 (sense) chosen to drop 1V at 80% of nominal lamp current. R1 (lamp) represents the lamp itself. R2 and R3 are in no way critical. T1 can be almost any low or medium power npn BJT. It could even be this forum's favorite - an opto-coupler - with suitable output configuration.

There are a thousand ways to detect lamp current, but this is one of the simplest.

[Burngate]

My old Vectra did it differently.
Across the lamp switch was a high-value resistor. With the switch off, the bulb held its positive terminal low, unless the bulb was blown, in which case the resistor pulled it high.

One drop-off by Vauxhall was the way they used that voltage, at least for the brake lights.
It was connected into the engine-management system, so a faulty brake light gave an engine fault warning.
So you're driving along without a care in the world - until that warning light came on. "STOP NOW BEFORE YOUR ENGINE BURSTS INTO FLAME"
So in panic you press the brake pedal, and the warning light goes off!
It would have been better to have a separate warning light.