SP505 4-Digit LCD



The Seiko SP505 1/2" display is a glass LCD panel. It is most easily driven by an integrated LCD/LED chip. Individual driver chips such as the 4543 can be used but the Maxim ICM7211ILP is made for just this type of display.

This is the circuit for a full clock using the SP505. Decimal Point2 is used in this clock as a "Paused" indicator. The colon flashes at 0.5Hz when the clock is running. Not shown in the schematic, but in the photo, is a proposed beeper circuit.


LCD timer schematic

LCD timer photoSP505 LCD


PCB overlay

The 7211 fits underneath the display. In the PCB layout here, pin 1 (5V) is marked. The track layout on the right is looking at a right-way-up display from the back.


display  bsf    reset     ;reset 4017, select digit 4 with q0=high
         nop
         bcf    reset

         movf   dg4,w     ;put value onto port pins
         movwf  porta
         call   delay     ;short delay (may be) necessary for LCD settling
         movf   dg3,w
         movwf  porta
         call   delay
         movf   dg2,w
         movwf  porta
         call   delay
         movf   dg1,w
         movwf  porta
         call   delay     ;after 4 data sent, 4017 is advanced to q4=1
         return

delay    movlw  10h       ;this value for use with 32768Hz crystal
         movwf  temp
inc      incfsz temp,f
         goto   inc
         bsf    clock      ;advance 4017 to select next digit
         nop
         bcf    clock
         return