Calculator Light Done!

I am finally done putting 30 5mm LED's in parallel into my TI83 silver calculator powered by 4 1.2nimh aaa's. Sorry but my digital camera is with my dad. I'll have pics friday.

When I was planning the project, one of you guys said that I needed a 40ohm resistor. With that installed, the blue and white LED's barely lit up. That is what is recommended for 1 LED, but with 30, it changed drastically. Tried 22ohm, same thing. Finally searched for an LED calculator, said I needed a 1omh resistor. I thought that the 16ga wiring gave enough resistance, so with no resistor, WOW! This thing lit up!

The bad thing is that when the LED's are running, the battery doesn't supply enough voltage to power the calculator. So.. might as well try to find some way to sneak some more cells in there.

I put 6 LED's directly in the front of the calculator. Do 5mm LED's really have 1 lumen each? I swear that the 6 make at least like 20 when I compare it to my e2e's mn03.

You are overdriving those LED's pretty bad. You really do need some resistors. Don't run them all through one resistor. Ideally, have a separate 40 ohm resistor for each led. But if that's too much hassle, having a 6.8 ohm resistor for each six leds (say) is better than one resistor for all 30 leds.

Why are you trying to turn your calculator into a flashlight?!

This calculator http://www.quickar.com/noqbestledcalc.htm says that with 4.8V supplied voltage with 3.6V accross the LED, 30ma desired current and 30 led's connected in parallel, I would need a 1.33ohm resistor. I'm not gonna use this a lot...maybe like an hour a week at MOST. So I don't really care if the LED's only have a life of like 100 or 200 hours. Thats like 2-4 years.

As for why I'm doing it... The case is clear, so might as well.

I think the ArcAAA puts out what 3-4lumens, or was it 6-7? So more than 1 lumen per LED is correct...

ideally, 30 MATCHED LED's, ie same forward voltage and current draw. If you have different colors there are different loads. Each grouping of colors would need a different current limiter, or only the reds and yellows would light up best. They have the lower Vf.
Jeff

Pics are up! They are at:

http://www.nifty-stuff.com/gallery/calulator-light

Thanks to reviewum for letting me use his gallery!

Yeah, the 6 "headlight" LED's produce at least half as much light as the mn03 as you can sorta tell from the beamshot comparison... so... maybe about 5 lumens each. Its pretty sweet. Not bad for a first-time "mod."

That is awesome!

Holy fudge! I am sitting at my desk, with my algebra homework in front of me, with my Ti-83 plus underneath my elbow as I'm typing!!! LOL! That is crazy! I have seen some cool looking silver editions, but none as cool as that! I wish I had a silver rather than a black one now. /ubbthreads/images/graemlins/frown.gif

Dude, FNinjaP90, send me an email with the pics and I'll post them for you! PM sent with info.

Wow! That is one cool calculator!
Nice job.