Anyone know of such a thing - self contained to run off 12 volts? Can get ones with a 50% duty cycle, but was looking for more like 1 flash per 10 seconds to cut down current consumption. And no room inside enclosure for more than a standard 5mm LED.
Dave Plowman (News) formulated the question :
Take a look at Maplins... Failing that, look at using a CMOS version of a 555 timer IC with an LED. The later would enable you to set some very long intervals between flashes.
I don't think you'll find one Dave - not that slow.
My favourite way of doing slow, low current flashing is the LM3909 - all you need is the chip, the led and a capacitor.
The current consumption is stupidly low, and it'll run off 1.5V. I had an alkaline D cell powering one of these for over 2 years.
Sub a 3mm LED, and use the spare space.
Great if you can find an LM3909 - they ceased production a few years back. A real shame as they were perfect for the application you describe.
I seem to recall a few going on eBay - for not more than a few pounds - so there's still some floating around...
Mathew
Problem is there's no space for anything other than the LED. And since you get self contained flashing LEDs - but with a 50% duty cycle - I was hoping there was something similar for my needs.
Grandata still stock them:
Didn't realise they'd been discontinued (wonder why?). I bought a tube of them ages ago, which lasted a good long while. I'll buy some up next time I come across them.
I'm guessing it was just lack of demand. I suppose there's only so many 'low-current-flashing-LED-and-nothing-else' applications you can think of before the novelty starts to wear off!
Now I look at it,
John Schmitt
The duty cycle and therefore current consumption is too high. I'm looking for perhaps one flash every 10 seconds, but bright enough to be seen in daylight.
You mentioned size being a limiting factor - may I ask what it's to go in? We might be able to think of some intuitive workaround/solution...
Back in the very early days (maybe 1990-92) of flashing LED's someone (maybe HP?) made one with 3 terminals that used an external capacitor to adjust the duty cycle, I think it had a forward voltage of around
7v so would still have needed a dropper resistor to run on 12v.
Never used to stop the electronics magazines with their annual variations on a theme of christmas gadgets.
Owain
It's part of the intruder sensor on a car alarm. Originally, it had a dim LED which didn't flash and you couldn't see in daylight. I replaced it with a bright flashing one, but there's no room for extra electronics - like a 555 - inside the case as there's already a PCB for the intruder sensor. I could re-wire it using multicore cable and site a timer elsewhere, but was looking for the easy option.
I'm trying to cut the quiescent current on a car sometimes not run for two weeks or more. At the moment it's over 150mA due to radio, alarm/immobiliser and central locking unit, etc.
You don't want a 555 anyway. They draw a ridiculous amount of current.
Get a battery conditioner? Or if the car isn't near the mains, use a motorsport battery switch to disconnect everything except the alarm? (More security, too.)
(My Cossie would flatten its battery completely in less than 2 weeks...)
I have had a good look around, and mostly they are kits, with wired components, I am sure you can create what you want out of the bits with a few changes. Ready made seems not to be an option.
John Schmitt
The CMOS one is fine. 7555 I've used this on the new central locking controller and got the quiescent down to .018mA. ;-) From 35mA. Mr Lucas wasn't to clever with circuit design in the '70s.
Car parked in the road.
Could do, but then the radio and OBC would loose their mememory - and I'd have no remote locking.
Yes. I'm being a tad genererous and assuming a fully charged battery.
Where have you been for the last 20 years? Use the CMOS version - 500ua maximum is hardly ridiculous.
Sorry, should have been 1mA absolute max over temperature range at 15V. Typically it will be a lot less.
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