Red LED displays

[Marcel Samek]

I am currently very enamored of red LED displays on calculators. I've been using my HP-67 a lot and find it so much more pleasant to look at than the dreary LCD on more modern calculators.

I am curious how much difference there was in the intensity, size, and crispness of various LED displays used on calculators. Were some considered "better" than others? And if so, which LED calculators are purported to have the best displays?

[walter b]

(02-12-2014 06:26 AM)Marcel Samek Wrote:  I am curious how much difference there was in the intensity, size, and crispness of various LED displays used on calculators. Were some considered "better" than others? And if so, which LED calculators are purported to have the best displays?

Hmmh, crispness? Seven segments stay seven segments forever, don't they? They may display 'Error' but that's it ...

Nevertheless those were nice displays though battery eating.

d:-/

[bshoring]

I also prefer the red LED displays.
Bob

[Marcel Samek]

(02-12-2014 06:31 AM)walter b Wrote:  Hmmh, crispness? Seven segments stay seven segments forever, don't they? They may display 'Error' but that's it ...

d

Well, maybe I chose a poor adjective. I believe that they have a magnifying material (plastic? glass?) in front of the segments. I would think that there would be some variation in the quality of the magnifying properties of that material and the quantity of light that it diffuses. That's just a guess however.... Anyway, the end result of how good the 7 segment display looks through the magnifier is what I mean by "crispness".

[HP67]

(02-12-2014 06:26 AM)Marcel Samek Wrote:  I am currently very enamored of red LED displays on calculators. I've been using my HP-67 a lot and find it so much more pleasant to look at than the dreary LCD on more modern calculators

Agreed. To this day I still don't like LCDs. I purposely didn't buy a 41 when they came out. Alas, those days are gone and now I'm happy to have LCD models rather than nothing.

[Joe Horn]

Of all the HP battery-powered calculators, I suspect that Topcat series had the largest LEDs, because the calculators were huge (not really handhelds). Here's a good comparison of the HP-67 vs. HP-97 LEDs. Look how big, bright and beautiful the '97 display is!


(Click image to see bigger version.)

[HP67]

What a gorgeous combo. Did the 97 use LEDs or Nixies?

[walter b]

(02-12-2014 09:00 AM)HP67 Wrote:  What a gorgeous combo. Did the 97 use LEDs or Nixies?

LEDs.

d:-)

[hp41cx]

[Siegfried]

I just got a HP45 and while I can't compare it side-to-side the display seems to be more readable than on the TI-30 I had in school. It's not so much the size but the viewing angle seems to be better on the HP.

If anyone ever fancies a steampunk redo of a HP nixie tubes would make for great looks. I found them fascinating on the butcher's scales as a kid. Readability is not that great, however because you have the shadows of all the other numbers.

[Didier Lachieze]

My Canon F7 has very big and bright led digits:



Different type of LED but still big and bright on my Sharp EL-112 & 814:

[HP67]

That's a beauty!

[Jim Horn]

LED technology has come a very long way since the days of HP's LED calculators in the 1970s. So, since my June 1975 HP-25 electronics has died, I considered re-engineering it to use higher efficiency LEDs and CMOS circuitry to get more performance and many days of use on a battery charge.

But that is not to be. Seven segment displays that will fit are apparently no longer available from *any* source I've been able to identify. The world has moved on to LCD, OLED and other ideas. While Avago (HP => Agilent => spinoffs) still makes small 5x7 dot matrix displays, they won't fit enough digits in the case - and cost a small fortune anyway.

So the original display will have to be used. At least when combined with CMOS and a modern battery chemistry the charge duration will still be greatly increased. At least the battery circuitry won't fry the electronics. And a 49 step memory will be greatly expanded too.

If anyone is aware of good displays for this, please let us all know!

Many thanks -

[everettr]

(02-12-2014 04:29 PM)Jim Horn Wrote:  LED technology has come a very long way since the days of HP's LED calculators in the 1970s. So, since my June 1975 HP-25 electronics has died, I considered re-engineering it to use higher efficiency LEDs and CMOS circuitry to get more performance and many days of use on a battery charge.

Have you looked at something like this?
http://www.adafruit.com/products/399#Description

This module is probably too large for the HP 25, since it is 71 mm long. There may be 1 or 2 mm that could be trimmed off the ends of the PCB?
It does have an RGB backlight, so you could get the traditional wavelengths coming out. I have not tried this one yet, but have heard that the contrast on these negative LCDs is low compared to LEDs or OLEDs. Of course, you would need modern electronics to talk SPI or I2C to the module.
I am curious as to the environment you would be using for development. I have thought about trying to take a lazy approach, using something like an Arduino Mega or maybe an Mbed, and dropping it into a repurposed case with a keyboard (HP 45, TI 55?). Scanning the keyboard matrix ought to be easy, and hooking up a standard serial LCD or OLED also.

[Jim Horn]

That LCD looks good. However, I still like the look of "real" LEDs. Reusing the original HP-25 display will ensure proper fit in the case behind the red window, too.

Development environment? I've not given that much thought yet, nor for which CPU to use. Having used the Cortex M-32 parts, the ARM environment is tempting even though those parts would be vast overkill. It is amazing what you can get in such a small package for a few dollars today...

With so many irons in the fire already, this project is on indefinite hold. But I hope to get into it before the year is out. I'm not in the class of the superb WP 34S team or the many other Forum regulars who have done marvelous things. But it would be nice to have my first calculator working again!

[Tugdual]

LCD was a real progresse in my opinion. I had a TI57 and I remember the stress of battery drained during exams. LEDs are just good for alarm clocks.
Now this below is a superior vintage display:

[John Keith]

(02-12-2014 04:29 PM)Jim Horn Wrote:  The world has moved on to LCD, OLED and other ideas.

I would love to see a calculator with an OLED display like that in a Samsung Galaxy phone. That would be the best of both worlds, IMHO.

John

[Katie Wasserman]

(02-12-2014 04:29 PM)Jim Horn Wrote:  But that is not to be. Seven segment displays that will fit are apparently no longer available from *any* source I've been able to identify. The world has moved on to LCD, OLED and other ideas. While Avago (HP => Agilent => spinoffs) still makes small 5x7 dot matrix displays, they won't fit enough digits in the case - and cost a small fortune anyway.

If anyone is aware of good displays for this, please let us all know!

I've considered doing this too. I would use the Avago alpha-numeric displays The serial interface, 5x7 dot matrix, color choice, small size and high efficiency look great for calculator use. Using the .15" height displays you should be able to get a 1 x 8 display + 1 x 4 display into the display space on HP Classic series calculator -- maybe not the Woodstocks, though. There's no magnifier bubble but I think a .15" display would be readable from about the same distance as the original 7-segment display (with bubble).

They are kind of expensive but not terrible.

[edit]

More on this...

Osram make a line of display similar to Avago's. The 1414 4-digit display here, should end-to-end stack to be 53.34mm when 3 are used. The Woodstock's display is just over 55mm so they should fit. But the small Avago display's are exactly the same size so they should fit too.