BUSICOM LE-80A Calculator

Miniature machine from the 70's based on a "calculator on a chip" LSI from Texas TMS0105BNC dated as 7303 (1973 week 03).

 

Schematics collected by direct observation. 

Elektronika MK 60 calculator

I had friends visiting family in Moscow during the summer.


And then they asked me about what I would like to have as a gift from there.

Well, my answer was simple:
Go to a street market and bring me a Russian pocket calculator! The older, the better.

Apparently shopping in street markets can be tricky and be very time consuming.
If you go to the central areas the asking prices is too high, then you spend hours commuting to reach the ones where the prices are lower and by the time you arrive there the fair is closing and most seller are gone.
So they spent a couple of days touring around. I felt a little bit guilty for steeling quality time from them, but hey, they asked!

And here it is.
It was dirty with marks of glue, has a few dents and the keys are scratched.

But is works nicely, as long as the environment light is strong enough to enable the solar panel.


This specimen was made in USSR on Sept-1988 (IX 88 on the back cover) and the official price was 45 Rubles.

The pouch is unusual but nice and soft.

Seven segment 8 digits LCD display, with 3 indicators on the right. From to to bottom:
"П" - Memory in use ( Память = Memory)
"_" - Minus signal
"Е" - Error

The factory seal is in place. It just takes a little steam to be removed without damage.

Time to dismantling the machine.

There is a white ink hand written label with a unknown number: 808039.

The serial number in the back cover is also 6 digits, but it is different: 847948

 
The SoC is a Russian КБ145ВХ3-2 made in 1988 week 08.

The 20µF/6.3V paper electrolytic capacitor was made in 1988 week 06.




This SoC operates from 1.5Volt nominal (with a minimum of 1.2V and a maximum of 1.8V), supplied by a 4 element solar panel, and consumes around 25µA.
This SoC contains 10,000 transistors to support a 5405 bits ROM microcode, RAM registers, ALU, keyboard scan, display decoding and control, synchronization unit and power supply.

I measured the solar panel under strong warm light (60 Watt at 40cm distance) and got 1.42Volt.
All four elements generates about the same voltage of 0.355 Volt. 
This is a little lower than expected but it happens that the capacitor is dry and has resistance leaking, so it is pulling down the power supply a little.

A uncommon design choice by today's standard was to use two АЛ102Г yellow LED diodes to protect the SoC from over-voltage. 

The schema can be downloaded from here.

CASIO fx-4100P Scientific Calculator

Another small pocket programmable scientific calculator from CASIO.
This one was assembled after 1991 week 14 according to the SoC date code.

Japanese industrial design with attention to detail
Color reverse painting labeling like Japanese used to do on pocket transistor radios from the 60's and 70's, many of them manufactured to be sold with American branding. 

Opening the case is done by undoing five small screws.
To remove the case I had to use a plastic pry tool to release the lateral latches before lifting the bottom side in order to be able to slide it down to release the top side.

Unusual CASIO choice of a SoC from Toshiba T9949A 9114H Japan.
Same remark for the large back cover shield, absent on most of CASIO machines from these series.

While I prefer the independent plastic keys approach like used in the fx-3600P, this rubber membrane key set is working fine and the labeling is resistant to wear; even after a vigorous cleaning with hand dish wash detergent in warm water it retained the full paint and color.  

CASIO fx-3600P scientific calculator

Made after 1985, according to the Hitachi HD43147 SoC processor.

Calculator forensics: arcsin(arccos(arctan(tan(cos(sin(9)))))) = 9.0000157179

Tested in DEG mode.
Typed: 9 sin cos tan INV tan INV cos INV sin
Result1: 9.000015718
Typed: - 9 =
Result2:  1.57179 -05
Typed: x 1000000 =
Result3: 15.7179

Front panel was lose due to film dry glue.

Single 3Volt CR2025 Lithium battery cell.

Two classic axial pass through mount 1/8 Watt, 5% resistors on the PCB back side.
Top = 390 Ohm, Bottom = 220KOhm

PCB front side.
Keyboard keys assembly (foil membrane attached to the PCB).

One unmarked SMD ceramic capacitor.
And the Hitachi HD43147  SoC processor, made in 1985 week 43 (5J 43).

Keyboard rubber membrane.

Real quality plastic keys, where the bottom half sports injection moding manufacturing.

 
Partial exploded view.