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can any boffins come up with a simple electronic circuit that when the ignition is switched off a flashing led is activated.got one at the moment wired via a switch though keep forgetting to put it on when leaving the car!
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When I had my old Cavalier, I wired mine in on a permanent live connection, and wired the -ve lead to a wire on the ignition switch. When the ignition switch was on, the feed was +ve, so the light didn't flash, but when off, the same wire grounded and then illuminated the LED.
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yeah daves rights, thats the best way to do it
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Why not just leave it on a live feed to flash all the time?
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well with all due respect Martin, I think it would drive mad while driving at night
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Dear oh dear you people do complicate things unnecessarily.
Available at all fine car accessory stores where I live: Flashing LED in self adhesive background (stick it where you like, as it were). Ends in 18"length of wire with battery clip for PP3 battery.
Cost (exc. Batteries): about 35p. Comes with impressive "WARNING" stickers for front side windows. No special electrical skills are involved so Mandarin langage abilities are not needed to decipher the instructions: A few minutes' training makes obvious to allbut the most mentally challenged the fact that plugging in battery causes LED to flash.
How do I know it works? I've used it on 6 of the cars I've owned here and haven't lost one yet.... ;+)
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I have used DD's method on my last 3 cars to good effect, espacially with a few scrounged Cobra alarm stickers from my local alarm installer.
I would not use a method which relies on having to switch the LED on or connect a battery on leaving the vehicle as this from time to time will get forgotten with the increased risk of the car being 'alf inched...
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Doesn't the Ka already have the PATS flashing light in the clock?
--
Adam
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Doesn't the Ka already have the PATS flashing light in the clock? -- Adam
Yes they do inside the clock.
--
Its not what you drive, its how you drive it! :-)
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On some cars that have parking lights operated by the indicator switch, there is a feed from the ignition that only becomes live when the ignition is off. I used this as a feed for the LED and it works fine, whenever the ignition is off, the LED comes on. There may be other circuits that become live when the ignition is off but the parking lights is an obvious one.
I'm no auto electrician but I'm a bit concerned with DD's method that the live from the ignition switch can't be guaranteed to ground when the ignition is off. Obviously it found an earth in the example given by DD because it worked but surely there's a danger that the circuit just becomes open circuit when the ignition off and therefore the LED wouldn't work - just a thought.
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I'm no auto electrician but I'm a bit concerned with DD's method that the live from the ignition switch can't be guaranteed to ground when the ignition is off.
Yes, you are quite right to point out that the live terminal from the ignition switch isn't connected to ground in a direct way when the ignition is switched off. However, even the resistance of the ignition and oil warning lamps* on the dashboard are low when compared to the LED, and therefore the voltage at this terminal is virtually at ground level.
* There are obviously other circuits in parallel, which reduce this effective resistance to earth still further.
Number_Cruncher
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Have wired up an led as DD stated and it works perfectly,does away with the need for switches or relying on a separate battery,and makes for an easy automatic deterrent.However just one thought,should a resistor be incoporated,or as I believe are flashing leds capable of handling more of a voltage/current than the non flashing variety
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Have you got the specs for the LED? Subtract the voltage drop from 12V*, and divide by the forward current to give an estimate of the *lowest* value of series resistor to use.
Sometimes these flashing LEDs come with an appropriate series resistor already in place, and the lead wires can be connected straight across the 12V supply. Check the spec.
When wiring in a plain LED, I would first try it in series with a 1K resistor, and measure the current to check against the LED spec, to make sure I had some margin - for some you can use 470R, but I would begin at 1K.
I suspect that as your LED hasn't blown already, it will probably be fine. But I would suggest that you check it out.
I hope that is helpful.
Number_Cruncher
* It's OK to say 12V, because while the engine is running and battery voltage is ~14V, there is no voltage drop across the diode. Also, the resistance calculated is the lowest value, a higher value should be used to give some margin.
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