EEVblog #1078 - World's Thinnest Calculator Teardown

[Fungus]

Sharp EL-540d vintage approximately 1984, does conversions with 2 key presses. First press yellow shift key then select desired (->bin) (->hex) ect. Also has (AND) (OR) (NOT) (XOR) (XNOR). Not RPN or graphing or programmable but good and under appreciated. Last calculator I ever bought.

Yes, that's how easy it should be. I like the way the hex input keys are directly above the numbers, too.

You can get a mint condition one for $30, too!

Looking around on eBay: The easy hex/dec/bin feature seems common to a lot of Sharp calculators, even the fancy newer models. Who knew? I might have to look into them and see if there's a model for me. Your 520D doesn't have a backspace button though, and I like those...

My unfashionable HP has one other killer feature: It converts degrees<->radians with a single (shifted) keypress. All scientific calculators have degrees/radians modes but not many will convert angles between them.

[rsjsouza]

Interesting simple base conversion with the Sharp: even a newer model seems to be a two button operation.
http://www.sharp-world.com/products/calculators/sc_calculator/el-w531/index.html

I will investigate and see if it uses larger than 32-bit precision. The TI-89 I had was capped in 32-bit, thus sold it and ended up getting a modern HP35S which goes to 36-bit - still a good calculator, but the base conversion is not that straightforward (although finger memory does wonders). The other calculator I have (HP48) goes to 40-bit, but I leave it at home as I am afraido to lose it

From Sharp I remember drooling over their pocket computers PC-1211 and PC-1500 back in the 1980s.

[rrinker]

 The Casio I used in college was much like that. It was the scientific one, forget the model number, with additonal keys on the fold out side. That was probably my all-time favorite calculator. It had all the common physical constants in it, plus it did logic, converted number bases between dec, hex, bin, and octal, converted between english and metric, and of course had all the requisite math and science functions. No graphing or programming, but didn't need that at the time. It was still my go-to years after graduation, until my first born decided to 'hide' it one day by putting it on top of a lamp where it wasn't immediately noticed, until the plastic had melted through and destroyed the secondary keyboard.
 I did learn how to use HP and their RPN, because if your calculator broke down in the midst of an exam, our one professor was all too happy to lend you one of his - except they were all HPs. I know more than one classmate got caught out by this. But my Casio never failed. It took a 75 watt light bulb to kill it.
 I remember those Sharp pocket computers (mostly from Radio Shack, not the original Sharp versions), but the one I actually had, the Radio Shack PC-4, was actually a Casio as well. I wish I had found it when cleaning out my Mom's house, but I must have lost it in a move long ago. The neatest thing I did with it was utilize the cassette motor control relay to drive a bigger relay  in a box full of D cell batteries to launch model rockets. They always look better if you can stand way back, but the stock launch controllers only had maybe a 20 foot cord, plus it used AA batteries which gave you maybe half a dozen launches. With my controller box plus a program in my pocket computer, my friend and I could BOTH stand back and watch.

 I have to say, kind of a shame to see this one destroyed, but it is also interesting to see how they pulled it off. More amazing when you consider when it was made. A calculator that thin would still be a marvel today. And to be made so cheaply it could be used for business promos. 

[Fungus]

A calculator that thin would still be a marvel today.

You can see there's no magic inside it, but actually doing it 0.8 mm thick takes some stubbornness.

I think they were mostly doing it to show off, not because it was necessary. If you look at Japanese calculators back then there's a whole load of them that were just trying to be the smallest, thinnest, most functions in a watch, etc.

eg.

(gotta love the gold bling finish)

And to be made so cheaply it could be used for business promos.

And also made to last by the looks of it - there's a layer of steel on front and back!

[MT]

Regarding the buttons:

Wouldn't the resistance change with pressure even if the carbon pads were always touching?
Maybe they work by looking for changes in resistance.

Yes it does, with all carbon/graphene pill key switching instead of logic sensing your matrix let a ADC sensing
the matrix. It's set up with velocity threshold points, works well with and without separator. Every sampling
boom box have done this for decades. Its called velocity sensing. If you quickly want a matrix keybed for your
projects buy a B9 pencil and plain paper then draw them out. I tested this back in the day with a HB class pen
recall mine did easily thousands of finger hits without wearing out. Or buy some conductive ink/paint, or
make your own.

[Fionn]

Just watched and found this text at 24:55 (in attachment)
What could it be?

[amyk]

It's very likely the IC was made by NEC, possibly even just the bare-die version of the same one as in these:

http://www.vintagecalculators.com/html/casio_mini_card_lc-78.html

How do these compare? Are they thicker but could actually be made thinner (and are not, because they would be too fragile?)

https://www.aliexpress.com/item/New-Portable-Ultra-Thin-Mini-Calculator-8-Digit-Credit-Card-Sized-Solar-Powered-Pocket-Calculator-Black/32819834728.html

(there are similar ones if you just search "ultra thin calculator", all at <$1 each.)