HP12c Speedup project



I've got a 1996 HP12C. The only flaw I find for this calculator is its slowness, so I have been very interested by the recent thread of Karl Schneider about the possibility to increase the speed of these kind of calcs.

The 1996 HP12C is a calculator-on-a-chip. Here is a picture of the CPU :

There is 2 CMS component linked in parralel with the CPU :

  • a dark one with 181J marking
  • a smaller grey one with KG2 marking

    I supose that the 181J is either the 180 uH inductor or the 180pF capacitor, but I don't know wich one. Any idea ?
    And what could be the KG2 component ? Is it a resistor ?



  • #3

    Bonjour Pierre,

    The 181J is a 180uH INDUCTOR manufactured by TDK (entre autres).

    Unfortunately, I have no idea about the KG2 origin.

    Cordialement/Best regards.



    The kg2 part is the cap.



    Thanks, Don & Etienne, for these informations.

    As it is easier for me to find capacitors than inductors, I first removed the KG2 capacitor, and try to run the calculator without it.
    What a surprise ! the calculator works perfectly, but now at warp speed. The ON-X test is completed in 3 seconds instead of 13.5 seconds usually, so a speedup factor of 4.5. I run the ON+ test during 10 mn without trouble, and the ON/ test is OK.

    Programs run nearly instantaneously, and financial calculations are very fast (time is money, you know that).

    Well, I recognise that it is suspicious that such an easy improvement have not already been made by HP. There will be probably drawback, so I keep watching my calculator during the next weeks.




    You may need some sort of inductance in order to stabilize the oscillator and/or keep the clock waveform decent. Without it the clock could be very susceptible to noise and tiny changes in the environment.

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