Possible to work nicely: adding LED to 3-volt power supply?

[bazzwazzle]

This is weird.. I wanted to add an LED to my calculator and it's running off 3-volts. Do any of you think it can be possible to add an LED without harmfully shrinking the last of the battery? I know this has nothing to do with stompboxes, but I didn't know where to go besides google and here ^_^. I haven't been here in awhile either, so hello again :wink:

edit: egads shoulda put this in the lounge guys. sorry about that.

[niftydog]

we talking a couple of 1.5VDC button batterys here? You would toast them so quickly with a LED that you'd probably go broke buying button batterys!

Even the wiz-bang high-end large silver oxide duracells max out at 180mAh at a current drain of only 1mA!

[bazzwazzle]

it's one solid 3-volt, but i doubt that would change anything lol.. or would it?

[sir_modulus]

maybe...get a real low power of high efficieny led, and run it nice and low (1 - 2 ma)...then you should be set

Cheers,

Nish

[bazzwazzle]

hmm ya. how many ohms would you think the resistor should be? (i'm not very good at figuring that out ^^).

If I really got bored, I could maybe replace the power supply with some AA's or a 9V   lol and patch it to the back or pouch it or somethin.

[niftydog]

V=IR
I=V/R
R=V/I

thus, for a quick and dirty 1mA calculation;
R= 3VDC / 1mA
R= 3kohms

But, to be done properly you need to take into acount the forward voltage drop of the LED you intend to use. Given that it's likely to be in the region of 2VDC, you're really looking at limiting the current through a resistor with 1VDC across it. Hence, replace the 3VDC with 1VDC in the above equation and you've got 1kohm.

[bazzwazzle]

ok I have located the + and - of this thing (it's very weird in here lol). I'm soldering a 1k to my LED and i'm gonna give this thing a try.

[bazzwazzle]

well it worked... but, the LED just wouldn't light up the whole LCD, only a portion of it. Maybe I'll just turn it into a power-on led.