yonubear
Posts: 90
Joined: Thu Sep 12, 2013 11:11 pm

Bulb sensor

Tue Sep 22, 2015 2:21 am

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
Posts: 3681
Joined: Fri Jun 08, 2012 6:03 pm

Re: Bulb sensor

Tue Sep 22, 2015 9:15 am

An Operational Amplifier setup to monitor current through the circuit to the bulb. No current and switch on = blown bulb.
Electronic and Computer Engineer
Pi Interests: Home Automation, IOT, Python and Tkinter

yonubear
Posts: 90
Joined: Thu Sep 12, 2013 11:11 pm

Re: Bulb sensor

Wed Sep 23, 2015 3:52 am

Thanks now to hunt up an example

grahamed
Posts: 277
Joined: Mon Jan 30, 2012 7:01 pm

Re: Bulb sensor

Wed Sep 23, 2015 7:25 pm

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
Posts: 277
Joined: Mon Jan 30, 2012 7:01 pm

Re: Bulb sensor

Wed Sep 23, 2015 9:11 pm

Hi

If you want an electronic version.
bulb sensor.jpg
bulb sensor.jpg (16.91 KiB) Viewed 822 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.

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Burngate
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Location: Berkshire UK Tralfamadore
Contact: Website

Re: Bulb sensor

Sun Sep 27, 2015 11:55 am

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.

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