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TTL Calculator

February, 2020:

I was particularly impressed with the way the Wang 360 worked - especially the way it multiplies and divides using logarithms instead of repeated addition.

I wanted to build a similar calculator 'from scratch' - using logic chips only (no calculator chips allowed).

September, 2020:

Settled on a design:

  • Interface:

    • 8-digit display​

      • positive integers only​

    • 0-9 keyboard

    • two internal 8-digit registers

      • "accumulator" for addition and subtraction​

      • "log accumulator" for multiplication and division

    • function keys:

      • "+" add to accumulator and display result​

      • "-" subtract from accumulator and display results

      • "x" multiply into log accumulator (add log of display to log accumulator)

      • "÷" divide into log accumulator (subtract log of display from log accumulator)

      • "Clr" clear the accumulator

      • "Disp" show the anti-log of the log accumulator (clears log accumulator)

  • Hardware:

    • based on AM2901 ALU and AM2910 sequence controller

    • microcode ROM modeled with Teensy 3.2 (it's easier to re-program than EPROMS)

    • the remainder are 74LSxx TTL chips

    • mixture of custom PC board and wire-wrap

June 2021:

Finally all assembled and working:

2021-06-06 fully built version.JPG
2021-06-06 CPU board.JPG

A close-up of the CPU board:

2021-06-06 Display board.JPG

Close-up of display board:

Here it is in action:

The steps are:

  • key in 25+ (adds 25 to accumulator)

  • key on 45+ (adds 35 to accumulator)

  • accumulator is displayed: 70

  • key in 33- (subtracts 33 from accumulator)

  • accumulator is displayed: 37

  • clear

  • key in 256x (calculates log(256) and adds to log accumulator)

  • key in 256x (calculates log(256) and adds to log accumulator)

  • Disp - displays anti-log of log accumulator (65536)

  • clear

  • then calculate 7894 x 562 to give 4436422 (real answer is 4436428 - close!)

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