Pages: 1 2 [3]   Go Down
Author Topic: Problems with voltage using a few leds  (Read 1731 times)
0 Members and 1 Guest are viewing this topic.
Global Moderator
Melbourne, Australia
Online Online
Brattain Member
*****
Karma: 511
Posts: 19323
Lua rocks!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

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:

Code:
(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.
Logged

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

Please post technical questions on the forum - not to me by personal message. Thanks a lot.

Offline Offline
Sr. Member
****
Karma: 7
Posts: 468
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

Valencia, Spain
Offline Offline
Faraday Member
**
Karma: 150
Posts: 5744
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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
« Last Edit: December 13, 2013, 03:48:45 am by fungus » Logged

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

Global Moderator
Melbourne, Australia
Online Online
Brattain Member
*****
Karma: 511
Posts: 19323
Lua rocks!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Interesting. Perhaps a 100 µF capacitor would be called for. But wouldn't it conceivably have an internal resistance which would drain the battery?
Logged

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

Please post technical questions on the forum - not to me by personal message. Thanks a lot.

Pages: 1 2 [3]   Go Up
Jump to: