26 August 2016

Olivetti Logos 262 PD desk calculator - keyboard map


In order to plug something in parallel to the keypad of the Olivetti Logos 262 PD desk calculator, I had to reverse engineer its layout. I did not want to open the keypad sandwich, so all work has been done through the exposed wires, pressing random keys while looking at the voltmeter.

First good news: voltages are within TTL range, about +5 V.

After fiddling for an hour or so I came to the conclusion that the 17 lines are split in 10 + 7, rows and columns if you wish.

I concentrated to map keys that I need to build a clock, so numbers, arithmetic operators and little more. The following table summarises the current state of work:

KEY12345678910
11121314151617



?











?

x


x










x






?









?

7




x








x

8





x







x

9






x






x

+







x





x











x




x




?










?






?









?


-/+



x








x


4




x







x


5





x






x


6






x





x


000







x




x












?



?





?









?



backspace


x








x








?







?



0




x






x



2





x





x



00






x




x



-







x



x













?


?






?








?








?







?









?






?




. (dot)




x





x




1





x




x




3






x



x













?


?














?

?




CE/CA

x







x









?






?










?





?











?




?












?



?













?


?














?

?















?
?





ACC

x












x
PRINT

x













x

Rows 1 and 2 are used by some switches that set the decimal precision, turn on/off the printer, etc. Positions marked with a question mark did something but I could not understand what, because  of the advanced functions of this amazing device (for the time it was designed!).

Once I connect these lines to a microcontroller I should be able to locate other keys with simple software loops. Now, how to hook it up to an Arduino?