HP-25C Eumulator

[Chris Chung]

Below is an ascii schematic, bypass cap, reset pull-up have been left out.

Code:


               MSP430G2553
             -----------------    
         /|\|                 |  
          | |                 | 
          --|RST  digit 0 P2.6|--\
            |     digit 1 P1.0|--\       digits bus (12)
            |     digit 2 P2.7|-----//--+---------+
            |     digit 3 P1.1|--/      |         ~  3 units of 4 digits bubble led
            |     digit 4 P1.2|--/      |         |
            |     digit 5 P1.3|--/      |    +---------+ +---------+ +---------+
            |     digit 6 P2.0|--/      |    | % % % % | | % % % % | | % % % % |----+
            |     digit 7 P1.4|--/      ~    +---------+ +---------+ +---------+    |
            |     digit 8 P1.5|--/      |                                           |
            |     digit 9 P2.1|--/      | digits bus x 3 scan lines                 |
            |     digit a P1.6|--/      +-----+-----+---/ ~~ /--+-----+-----+-----+ |
            |     digit b P1.7|--/  _=_ | _=_ | _=_ | _/ ~~ /=_ | _=_ | _=_ | _=_ | |
            |      scan X P2.5|-----o o-+-o o-+-o o-+-/ ~~ /o o-+-o o-+-o o-+-o o-+ |
            |      scan Y P2.4|-----o o-+-o o-+-o o-+/ ~~ /-o o-+-o o-+-o o-+-o o-+ |
            |      scan Z P2.3|-----o o-+-o o-+-o o-/ ~~ /+-o o-+-o o-+-o o-+-o o-+ |
            |                 |                                                     ~
            |                 |      (34 tactile button + 1 slide switch populated) |
            |                 |                                                     |
            |                 |        +--------+                                   |
            |             P2.2|--+---->|CLK ~CLR|---+---- Vcc                       |
            |                 |  |     |       B|---+                               |
            |                 |  |     |  0(d)QA|-\                                 |
            |                 |  |     |  1(f)QB|-\                segments bus (8) |
            |                 |  -     |  2(b)QC|--------------//-------------------+
            |                 | | |    |  3(a)QD|-/
            |                 | | |1k  |  4(g)QE|-/  74hc164 segment driver
            |                 |  -     |  5(e)QF|-/
            |                 |  |     |  6(c)QG|-/
            |                 |  +---->|A 7(h)QH|-/
            |                 |  |     +--------+
            |                 | === (102)    1 wire shift register via RC delay
            |                 | ===  1nF     to shift 1, Hi-Low-Hi
            +-----------------+  |           to shift 0, Hi-Looooooow-Hi (>20us Lo)
                                ___
                                ///

Being a minimalist I always go for the most simple design. The led modules are driven directly by the MCU (digits) and a 8 bit shift register (segments).
All of the 16 IO lines on the MCU is used. 12 IO pins are used to drive the LED digits, also used for key scanning columns. 3 IO pins for key scanning rows. The last single IO pin is used to drive the shift register.
The LED is not the brightest as there are no dedicated driver. So it has trouble for outdoor usage.
The MCU is rather limited but I really want to use only thru-hole parts so it's easier to build.