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### Topic: Problems with voltage using a few leds (Read 4210 times)previous topic - next topic

#### Nick Gammon

#30
##### Dec 12, 2013, 11:11 pm
By my calculations, around 2 years.

Disregarding the approximate constant drain of 5 µA while asleep, to flash the LED at 20 mA it should be:

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` (210 / 20) * 2000 / 24 / 365 = 2.39 years`

Assuming 210 mAH from the battery, taken for 1 mS every 2 seconds (therefore you get 2000 times as long), divided by 24 hours in a day and 365 days in a year: 2.39 years.

Put it like this, it's still flashing and it started on around 12th October 2013.
Please post technical questions on the forum, not by personal message. Thanks!

http://www.gammon.com.au/electronics

#### UnoDueTre

#31
##### Dec 12, 2013, 11:40 pm
Thanks Nick.
Handy little circuit, can think of other uses for it as well.
By using the newer so called super bright LEDs running at 10mA instead and also one of those silvered reflectors for the LED for some optical gain (but with reduced viewing angle) one could increase the life span of 2.4 years by a considerable amount.

#### fungus

#32
##### Dec 13, 2013, 09:46 amLast Edit: Dec 13, 2013, 09:48 am by fungus Reason: 1

OK, it's an AtTiny85, but that would draw about the same when asleep.

Sleeping, sure. Maybe even with all the timers/ADC/etc turned off, but Lilypads normally don't do that.

PS: No capacitor on your gadget? Keeping a little ceramic capacitor charged would make the battery last much longer. High current pulses are bad for them, see: http://www.ti.com/lit/wp/swra349/swra349.pdf
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

#### Nick Gammon

#33
##### Dec 13, 2013, 10:43 am
Interesting. Perhaps a 100 µF capacitor would be called for. But wouldn't it conceivably have an internal resistance which would drain the battery?
Please post technical questions on the forum, not by personal message. Thanks!

http://www.gammon.com.au/electronics

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