Re: TI-H: Battery question
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Re: TI-H: Battery question
>I'm currently working on a backlighting project for the TI-8x series
>(and possibly the 92...), but I'm perplexed by one thing:
>
>I'm using 3 LEDs, each which require about 2V to light up. I'm
>connecting them in a parallel circuit, something like you see here:
>
> ----LED----
> / \
>-------|-----LED-----|-------
>| \ / |
>| \----LED----/ |
>| |
>+ -
>
>(with a switch, of course)
>
>My question is: is it possible to hook this circuit directly to the
>TI's batteries, or would it be better (yet more complex) to use a
>seperate battery?
You can hook it up directly to the batteries, but you will need to add
a series resistor otherwise you'll blow out the LEDs. The batteries
output about 1.5 volts each or 6 volts total, and if each LED requires
perhaps 5 milliamps (a guess, current draw varies widely for different
LEDs and different desired brightnesses) and have Vforward "turn on"
voltages of 1.7 volts each, then the ohms law calculation is as
follows:
Resistor value = (6V-1.7V) / (3*0.005)
Which comes out to about 286 ohms for 3 such LEDs connected in
parallel.
-Mel
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-The TI-Memory Expansion Homepage
-http://www.egr.msu.edu/~tsaimelv/expander.htm
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