Re: TI-H: EL Backlights?
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Re: TI-H: EL Backlights?
From: <Cyong0@aol.com>
> What's the difference between EL Backlights and other backlights.
There are basicly two types of backlight used on the calc, EL and LED. LED
backlights are generally done with 6 or so LEDs shining into the edge of the
LCD from the lower edge. In general the LCD is not uniformly lit, but if
done properly one can achieve very good results. I'd particularly like to
see one done with some rectangular backlighting LEDs.
EL backlighting gives more uniform light, but does require an inverter to
provide the high voltage AC to drive it (typical 40VAC or more. The
inverters I used ran at about 80VAC 400cps). I prefer EL backlighting,
mostly because of the uniformity of the light, but LED backlighting has
fewer potential problems.
>I really
> need a backlighted 89 (since I do a lot of my work in the car at night)
and I
> was wondering if anybody out there knows how to install them (with
> confidence:P)
Certainly, I've sold about 25 EL kits and installed about 10, and 2 LED
type.
> I really need to get myself a TI-89 w/backlighting, either
Electroluminescent
> or another good type, and am hoping that somebody out there can do it.
Does
> anybody know how much one of these things cost?
Depends on how much of it you do yourself. A nicely done LED backlight
could be done for under $15 with minimal modifications to the LCD. And
thats assuming you have to go buy parts, if you have even a small junk box
you could probably do it for $5.
> If anybody can do this, or just has some advice on whether EL Backlighting
is
> better or other types, please e-mail me...
EL backlighting is more expensive and more difficult to do, but (IMO) yeilds
a better backlight. LED backlighting is cheaper, easier to get parts for,
and easier to install.
> also e-mail me if you think I can do it myself
Anyone who can pay attention to details, work carefully and follow
instructions can handle it. It should be aproched with the mentality of a
model builder, its important to keep things neat and careful. If you just
try to get it done it will probably look like crap.
> As well as where I would get the parts
Local electronics stores, www.digikey.com or www.mouser.com would be good
places to start. Basically you need a switch, something to mount the LEDs
with (clear epoxy would be good) and some LEDs, preferably the flat
rectangular type instead of the round type. Even better would be about 10
of those little surface mount LEDs (in which case mounting them on a
PCB-like material would be good), or probably the best, LED backlight bars.
These are small plastic bars a couple of mm on a side, and up to a couple
of cm long. They have a number of LED junctions incased in a milky plastic
that diffuses the light so that you don't get that 'spotlight' effect you
sometimes see in LED backlights.
I would recommend you get a few of those flat rectangular LEDs (buy or
salvage from old electronic equipment). If you have enough you can mount
them so that they form a continuous bar across the bottom of the LCD,
otherwise space them evenly. You could arrange the LEDs on a piece of paper
and then embed them in some clear epoxy to hold them together. It might be
possible to add something to the epoxy to make it milky so that it will
diffuse the light from the LEDs.
The electrical connection will depend a bit on what kind of LEDs you get.
Your power supply voltage will be up to 6v (and down to somewhere around 4
volts probably); a typical red LED will drop 2v, so you can hook up 2 or
more in series to run them. You can also use one or more resistors sized to
limit the current through the LEDs to whatever they are rated for (varies by
LED, typically not more than 20mA continuous).
Visit my web page to see more details about installing an EL backlight.
http://www.genetech.net/~dknaack
I believe there is a link to an LED backlight on the TI-Calc web page too.
DK
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