Re: TI-H: NS Illuminator

To: ti-hardware@lists.ticalc.org
Subject: Re: TI-H: NS Illuminator
From: tsaimelv@pilot.msu.edu (Mel Tsai)
Date: Wed, 08 Oct 1997 06:12:36 GMT
In-Reply-To: <971007215747_1148031706@emout17.mail.aol.com>
References: <971007215747_1148031706@emout17.mail.aol.com>
Reply-To: ti-hardware@lists.ticalc.org

>battery clip inside, holding...drumroll please...2 AA batteries.  That gives
>3.0 volts with new batteries.  The LED should get a max 2.8 volts, so 3.0 is
>too much.  The typical voltage to the LED should be 2.1 volts.  I use a diode
>to step the 3.0 down to 2.4 (standard silicon diode, .6 volt drop).  Then it
>can be put through the switch and into the LED.  It works well.  

Umm, this is not a standard practice... Generally you would use a
resistor.  Being a nonlinear device, adding a diode in series is
highly innaccurate at best and can even be dangerous.  I'm surprised
it works without burning out one of the components.  

Use a resistor instead and experiment with different sizes (you can
calculate exactly which value you need, but that'll take me too long
to explain :).  This way you keep the circuit first-order nonlinear
instead of varying with e^2, which is what happens with adding a
second diode (in lamen's terms, a resistor is better and more
efficient :).

-Mel
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-The TI-Memory Expansion Homepage
-http://www.egr.msu.edu/~tsaimelv/expander.htm

References:

Re: TI-H: NS Illuminator

From: NDStein@aol.com