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02-04-2014, 11:51 PM

I'm curious about adding a small LED to backlight the screen. I use daily a 50g so the size of it's screen may require two or more to light the entire surface. Has anyone known of any guides around, or done it themselves?

John R · 02-05-2014, 03:56 AM

You might want to check this out:

HP-42S with Electroluminescent Screen and Simple I/O Port

Garth Wilson · 02-05-2014, 04:48 AM

Keep in mind that a backlit LCD is not the same as a non-backlit one plus a back light. If you look at off-the-shelf LCDs in catalogs, you will see reflective ones, transflective ones, and transmissive ones. The reflective ones are made to have be best visibility in normal to high-light conditions, including in full sunlight. They cannot really be backlit. The light simply does not come through from the back. Transmissive ones almost require backlighting to be seen at all, but aren't very usable in bright light. Transflective ones can be seen without the backlight, but visibility is not very good.

02-05-2014, 11:46 PM

Interesting sources, thanks! I'm going to need to do a lot more research before I get brave enough to open up my 50g and start modifying it.

dizzy · 02-06-2014, 12:24 PM

(02-05-2014 11:46 PM)mindheavy Wrote: Interesting sources, thanks! I'm going to need to do a lot more research before I get brave enough to open up my 50g and start modifying it.

This is something I've thought about; I'll be interested to hear how you get on if you try. Another possibility is attaching an LED light to the calculator somehow, so that it illuminates the display. Sadly, the USB port can't be leveraged for power, but it could possibly be used as a mounting point for self-powered light. I haven't found an ideal solution yet.

Mike Morrow · (This post was last modified: 02-10-2014 06:32 PM by Mike Morrow.)

(02-04-2014 11:51 PM)mindheavy Wrote: I'm curious about adding a small LED to backlight the screen.

Have you seriously considered the additional current drain of four to six edge-mounted LEDs on the four AAA cells of a HP 50G...a calculator infamous as a battery eater even without such additional draw?

I've never had reason to use my calculators in the dark, except the HP-67 that I used 35 years ago to compute "closest-point-of-approach" of surface contacts on my submarine (and then those HP-67 LEDs looked so pretty)! :-)

Steve Simpkin · 02-10-2014, 09:58 PM

You could always use an LED Headlamp. It would look pretty geeky but I'm thinking that is not an issue for our crowd Smile

I am still remembering how "cool" I must have looked walking down the High School hallway with an HP-25 calculator hanging from my belt. An elegant calculating weapon for a more civilized age. Good times... Good times....

davetheguru · 02-11-2014, 03:51 AM

(02-10-2014 09:58 PM)Steve Simpkin Wrote: I am still remembering how "cool" I must have looked walking down the High School hallway with an HP-25 calculator hanging from my belt. An elegant calculating weapon for a more civilized age. Good times... Good times....

A true Jedi wore a slide rule on their belt. Yes, I'm old enough to go back to the clone wars.

chriss · (This post was last modified: 02-11-2014 11:03 PM by chriss.)

(02-10-2014 09:58 PM)Steve Simpkin Wrote: You could always use an LED Headlamp. It would look pretty geeky but I'm thinking that is not an issue for our crowd

Many a time I've packed my 50g and a head torch in my bag, but never have the two needed to be used together. Yet. I'm sure I'll find an excuse now at least someone thinks it might be socially acceptable Smile

Steve Simpkin · 02-11-2014, 11:41 PM

(02-11-2014 11:03 PM)chriss Wrote: Many a time I've packed my 50g and a head torch in my bag, but never have the two needed to be used together. Yet. I'm sure I'll find an excuse now at least someone thinks it might be socially acceptable

Yeah... I would consider the source of that commentary before wandering out in public like that. Me and "socially acceptable" are an award mix.

Dave Frederickson · (This post was last modified: 05-30-2014 01:10 AM by Dave Frederickson.)

TAS #### looks like a backlit 28S.

JimP · 05-29-2014, 09:07 AM

(02-04-2014 11:51 PM)mindheavy Wrote: I'm curious about adding a small LED to backlight the screen. I use daily a 50g so the size of it's screen may require two or more to light the entire surface. Has anyone known of any guides around, or done it themselves?

Never done it on HP hardware, but doesn't the Casio FX-9860G Slim (one of the best monochrome displays) have one built in?

**Katie Wasserman** · 05-29-2014, 07:25 PM

(05-29-2014 09:07 AM)JimP Wrote:
(02-04-2014 11:51 PM)mindheavy Wrote: I'm curious about adding a small LED to backlight the screen. I use daily a 50g so the size of it's screen may require two or more to light the entire surface. Has anyone known of any guides around, or done it themselves?

Never done it on HP hardware, but doesn't the Casio FX-9860G Slim (one of the best monochrome displays) have one built in?

It does indeed and it's extremely nice looking. Perfectly evenly lit with reasonably low power consumption. The idle current draw on the "slim" is about 0.5ma (30ua in the off state) from the 2 AAA batteries. With the backlight on this goes up to about 10ma. So you could run it with the backlight on for about 100 hours on a pair of AAA alkaline cells. While you can't control the intensity of the backlight (it seems perfect to me as they have it) you can determine how it turns on and when it will turn off, automatically or not.

Also, there are 2 or 3 RPN calculators "apps" for the fx9860, if you must have RPN.

Dave Frederickson · 05-30-2014, 01:09 AM

Getting back on-topic ...

Yes, it IS a backlit HP-28S!

[Image: Backlit+28S.jpg]

Anyone know how this mod was performed?

Dave

John R · 05-30-2014, 02:51 AM

(05-30-2014 01:09 AM)Dave Frederickson Wrote: Getting back on-topic ...

Yes, it IS a backlit HP-28S!

Anyone know how this mod was performed?

Dave

I don't think it's backlit. I think it's just fortuitous lighting and camera placement, with the light source above the top border of the photo, and forward-scattering off the LCD screen to the camera location.

Dave Frederickson · (This post was last modified: 05-30-2014 03:09 AM by Dave Frederickson.)

Upon further examination, I agree. I guess it's back to Casio calcs.

Jim Horn · 05-30-2014, 11:37 PM

Mr. Ignorant here - doesn't the Prime's color LCD include back lighting?

GeorgeOfTheJungle · 05-31-2014, 12:12 AM

(05-30-2014 01:09 AM)Dave Frederickson Wrote: Anyone know how this mod was performed?

With photoshop!

Dave Frederickson · (This post was last modified: 05-31-2014 12:29 AM by Dave Frederickson.)

(05-31-2014 12:12 AM)GeorgeOfTheJungle Wrote:
(05-30-2014 01:09 AM)Dave Frederickson Wrote: Anyone know how this mod was performed?

With photoshop!

No. John R got it right.

(05-30-2014 11:37 PM)Jim Horn Wrote: Mr. Ignorant here - doesn't the Prime's color LCD include back lighting?

Yes, but we're drifting off-topic, again. I believe mindheavy's OP was with regard to calculators that have had a backlight added, like the post by John R.

Anyway, mindheavy hasn't clocked-in to the Forum in too long and is now Unregistered. So I'll take the blame for keeping this thread alive past it's expiration date.

Moving on, Dave

**Katie Wasserman** · 05-31-2014, 04:38 AM

Have you looked at the project to add a backlight to the HP100LX/200LX? This became a commercial enterprise for a while. But I think ended because it was expensive, difficult and the market for it was drying up. There's a lot of information out there on this including videos, etc.. This idea was to remove the reflective foil on the back of the LCD and replace it with a semi-transparent one that would let the backlight through.

Here are the step-by-step details.