EEVblog #1078 - World's Thinnest Calculator Teardown

[EEVblog]

A look at the amazing construction techniques used in the world's thinnest calculator by Casio
Destructive teardown on the Casio SL800 credit card calculator from 1983.
It's more interesting than expected!

[DeanCording]

Those caps would probably be for power storage for the solar cell.

[Bud]

I've seen iso 7816 cards that make sound, cards with Red 7-segment LED looking display, and cards with a fingerprint sensor 

[Mr. Scram]

It pains me to see it destroyed, but it was for the benefit of us all.

[Rerouter]

So now the question falls to you dave, can you find glassless LCD's and build using reccessed capacitors to make a V2 of your prototype with a much tighter PCB sandwitch

On the topic of very thin boards, How would you describe to a PCB house to have a routed out area that does not cut through the entire board cross section, a dip or a void with the opposite surface left intact?

[Tek_TDS220]

Looks like a layer or two of prepreg to me, not flat-flex.  You can tell by cutting through the board.  You'll see fibers if it is prepreg.  A variety of prepregs are commonly available down to 60 um (with 106 glass).

[EEVblog]

So now the question falls to you dave, can you find glassless LCD's and build using reccessed capacitors to make a V2 of your prototype with a much tighter PCB sandwitch

Oh boy, don't me started...

On the topic of very thin boards, How would you describe to a PCB house to have a routed out area that does not cut through the entire board cross section, a dip or a void with the opposite surface left intact?

Two ways:
1) Controlled depth route. Not very effective/useless on thin boards. But cheap'n'cheerful.
2) Tell them to route the pre-preg layers first before they glue them. This will incur extra cost, but it will give you a perfect recess. Easy if you are already doing a multi-board, especially with bling /burried vias. On a standard double sided board they'll have the make up the board thickness with multiple pre-pregs. Something easy would be say 0.8mm + 0.8mm with 0.8mm depth route.

[Fungus]

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.


Edit: Now watch the prices of these skyrocket on eBay.

[gamalot]

I once had one Casio look like this when I was in high school in the late 80s.

[EEVblog]

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.

I wouldn't want to engineer it like that. The spacing seems quite deliberate.

[Fungus]

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.

I wouldn't want to engineer it like that.

You might not have a choice if the requirement is "0.8mm".

I don't see why it would be more difficult than the capacitive sensors on your watch.

[VEGETA]

Isn't it the time for engineering calculator shootout? I used to own a Casio (a silver one) which costs around 25$. I wonder what is the best these days for someone to buy, this could be a nice topic for a new video.

I think credit-card sized calculators are nice, but are they practical? I mean, do people really use them instead of real calcs?

[Fungus]

Isn't it the time for engineering calculator shootout? I used to own a Casio (a silver one) which costs around 25$. I wonder what is the best these days for someone to buy, this could be a nice topic for a new video.

a) What do you define as "engineering"?
b) Isn't there an app for that?
c) It wouldn't be impartial, Dave is very brand-biased. 

GOTO 27m40s

I think credit-card sized calculators are nice, but are they practical? I mean, do people really use them instead of real calcs?

I remember people using them back in the day. Mostly they were freebie/promo giveaways like the on in this video.

These days people use their smartphones.

[EEVblog]

You might not have a choice if the requirement is "0.8mm".
I don't see why it would be more difficult than the capacitive sensors on your watch.

Totally doable with separated distance in 0.8mm IMO.
Also, if all the keys touched all the time, that's a lot of extra current draw in idle, plus the requirement to measure it in a meaningful amount of time if it's high resistance.

[TheSteve]

Not in the same ballpark thickness wise but probably inspired by the calculator.

The Motorola "Confidant" numeric credit card pager.

[Rerouter]

Well to get you started, it appears there are single color, flexible reflective lcd's on alibaba that resemble the one shown in the video.
Find one in the right form factor, and you may be set for a very thin screen.
https://www.alibaba.com/product-detail/flexible-transparent-display-flexible-transparent-lcd_60667954126.html?spm=a2700.7724857.main07.141.26471f05NcMM24

Combine it with the printable solar panel flims like mikeselectricstuff reveiwed and you could just pull of a modern version.

Then using something like this for power (not insane power density, but for an LCD calculator, it should be low)
https://www.digikey.com/products/en/capacitors/electric-double-layer-capacitors-edlc-supercapacitors/61?k=&pkeyword=&pv1500=1231&FV=ffe0003d&quantity=0&ColumnSort=0&page=1&pageSize=25

[Skashkash]

 Air pressure helps to provide a "spring" effect to keep the conductive carbon away from the pcb contacts.
 
  It's why you have that inner spacer layer with channels between buttons to equalize the pressure between the switch "cells" when you press a button. 

Had similar (but much larger) keyboards on some equipment back in the 80's. If the plastic got punctured over one of the buttons, the top layer would actually deflate and we'd have to toss whole keyboard.

[blackjetrock]

You can get at the die with a torch, no acid required:



Also, I have an Olympus like yours (I got it after I saw yours...) and I have a nice XY slide holder so you can move stuff around. Did yours not come with one? They are available on ebay quite cheaply.

[Fungus]

Totally doable with separated distance in 0.8mm IMO.

Ok, I can't claim to be an expert there.

Also, if all the keys touched all the time, that's a lot of extra current draw in idle

Not necessarily true if it's doing a matrix scan - not all the keys will be powered up all the time.

Plus: Does it matter in a solar powered device? So long as it works under normal conditions (single keypresses) then it's fine.

But, whatever. If you don't see any problems with tolerances for the keypads then we'll do it that way.

[rsjsouza]

Also, if all the keys touched all the time, that's a lot of extra current draw in idle

You gave me something to think about. I recall that if you pressed several keys on some old calculators the LCD would dim considerably - I never thought that power consumption could be a possible cause.

Dave, you rave about Casios and I grew up loving them as well, but in terms of durability they leave a lot to be desired. They seem to have embraced more than anyone the zeitgeist of disposable electronics of the 80's: I have several 1980 and 1990's calculators/scedulers/gizmos from them (including a "film card" SL760, several fx-39, among others) that have their crappy membrane keyboards partially or totally inoperative after 15, 20 years of age. Multiple HPs and TIs of the time are still running quite strong.

[Fungus]

Dave, you rave about Casios and I grew up loving them as well, but in terms of durability they leave a lot to be desired.

There was a time when they were really good. I remember my FX-180P fondly.


After that they went downhill IMHO, especially the keyboards.

Multiple HPs and TIs of the time are still running quite strong.

I'm not a TI fan but HP made some good, solid, basic scientific calculators that have lasted. The calculators I use today are old HPs.

nb. I'm not a fan of graphing calculators in general, I only need a basic scientific model for what I do.

This thread is now doomed to turn into a flamewar.

[rsjsouza]

Dave, you rave about Casios and I grew up loving them as well, but in terms of durability they leave a lot to be desired.

There was a time when they were really good. I remember my FX-180P fondly.


After that they went downhill IMHO, especially the keyboards.

My units are older than this and their keyboards started to fail some 10~15 years ago...

Multiple HPs and TIs of the time are still running quite strong.

I'm not a TI fan but HP made some good, solid, basic scientific calculators that have lasted. The calculators I use today are old HPs.

To me the TI calculators of the 70's-80s still have good working condition keyboards (TI-30, a couple of TI-59s, a TI-66). I also have a pair of HP11Cs and HP48S and GX (well into the 90's) which are still pretty solid.

This thread is now doomed to turn into a flamewar.

[Fungus]

There was a time when they were really good. I remember my FX-180P fondly.

My units are older than this and their keyboards started to fail some 10~15 years ago...

I'm not sure what happened to my FX180P. Lost in the mists of time somewhere.

To me the TI calculators of the 70's-80s still have good working condition keyboards (TI-30, a couple of TI-59s, a TI-66). I also have a pair of HP11Cs and HP48S and GX (well into the 90's) which are still pretty solid.

I've got the obligatory HP11C but I really like my HP 20S. It's not a famous model but it has all the right functions and layout for me. It does hex/dec/bin conversions with very little fuss. I don't know any other calculator which does those without half a dozen keypresses or you have to go into a special mode first.

[bjcuizon]

Thats a thin as calculator right there. I just skipped a bit when Dave destroyed it   .
I also have something similar...its an "IMA" branded calculator, Model No. LC-684. Maybe late 1980's to 1990's era. It is also solar powered but its like 2mm thick so I think it still doesn't beat Daves one.

[chickenHeadKnob]

I've got the obligatory HP11C but I really like my HP 20S. It's not a famous model but it has all the right functions and layout for me. It does hex/dec/bin conversions with very little fuss. I don't know any other calculator which does those without half a dozen keypresses or you have to go into a special mode first.

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. I started out as  a calculator nerd teenager/young adult and then the urges slowly left me for good.

Here is a pic:https://www.ebay.com/itm/MINT-RARE-Sharp-EL-540D-Solar-Power-Scientific-Calculator-MANUAL-EL540-/162937868447