Now I've got your attention, if you were fitting some alarm LEDs to a car
- and wanted to keep power consumption to a minimum while having them as bright as possible, what sort of gap would you have between flashes - and how long for the flash itself?
It's keeping me awake at night. ;-)
If it was un-missably bright, 1/10th or maybe 1/20th on and 4-5 seconds off, hopefully it won't be using a blue LED?
eye responds to peak intensity so as short as you can and as bright as you can.
I think anything over 20ms wont get averaged out..
I would personally go and dig in a bunch of old links and find this:
which blinks whenever, but for long, using used batteries.
If you're look at programming/designing it, I'd go for a small fraction of a second, and no more than five seconds pause, else someone considering a car for theft might miss it...
Thomas Prufer
Modern LEDs have become so efficient that you probably don't have to try very hard. CMOS 7555 timer IC and an LED 10mS on 5-10s off. Peak current limited to 30mA (though that may be too bright!)
You could find lower current solutions but under 100uA should be pretty harmless compared to the self discharge rate of a lead acid car battery.
I built one about 15 years ago on the same criteria (and for a Rover! Tho a 214Si) and went for something like 10mS/2S. Used whatever the brightest red LEDs were available at the time at Maplins (ie probably less powerful than now) and pulsed at max continuous current. Being such a short pulse I could have actually upped it a fair bit. Expected life from a decent charge was years!
So far, so whatnot.
However, when it was fitted it was just tooooo bright. It was mounted in the centre console pointing backwards and was really obvious in daylight. Great. But at night, when the glass was misted up it illuminated the whole rear screen in red.
Always meant to put a black dot in the middle of the LED to try and reduce this effect while keeping the edges bright but never got a round tuit.
Scott
Mine is operated off the alarm/immobiliser, so can be as bright as possible as only on when the car is not in use. I've mounted two LEDs in the front door lock buttons having seen this on a production car. The theory being a thief would try the doors first.
I reckon somewhere between 1/20-1/10th second on cycle, 0.5-1.0 Hz overall rate and use blue (more visibility for your amps).
I put this one on the ignition so it ran whenever the key was out of the ignition which gets over worrying about not locking etc!
I'd be worried of being too bright in case it actually attracts attention.
Scott
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