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.
