Projects Log

Persistence Of Vision + Leds = Fun

21 July 2006

Today I saw an article about POV by Erik Zoltan (link IBM via hacked gadgets)

He's using a Parallax HomeWork Board (I don't know the price but i think it's quite expensive) thus I've decided to do the same thing with low cost equipement (16F84)

1) the electronical part

why do I use a 16F84:

i have some

it's cheap

you do not need a lot to make it work (1 crystal, 2 capacitors)

port pins have "Direct LED drive" capability

not that hard to program

The board:

board
as you can see, you do not need to have a lot of stuff on the board

The pin diagram
16f84 pin diagram

The schematic diagram

R=120 ohm
C=15pF
X=4Mhz

2) The assembly code part

STATUS equ 03h ; Status Register
TRISA equ 85h ; TrisA Register
PORTA equ 05h ; A Port
TRISB equ 86h ; TrisB Register
PORTB equ 06h ; B Port
COUNT1 equ 0Ch ; delay loop counter

P equ 0Eh ; pointer
C equ 0Fh ; display counter

FSR equ 04h ; File Select Register
INDF equ 00h ; Uses contents of FSR to address Data Memory

bsf STATUS,5 ; ==> Bank 1
movlw 00h ; B port
movwf TRISB ; output
bcf STATUS,5 ; ==> Bank 0

movlw b'11000000'
movwf 10h
movlw b'01111111'
movwf 11h
movlw b'00010000'
movwf 12h
movlw b'00001000'
movwf 13h
movlw b'00010100'
movwf 14h
movlw b'00100010'
movwf 15h
movlw b'11000001'
movwf 16h
movlw b'00000000'
movwf 17h
movlw b'00000000'
movwf 18h
movlw b'00111100'
movwf 19h
movlw b'01001010'
movwf 1ah
movlw b'01001010'
movwf 1bh
movlw b'00101100'
movwf 1ch
movlw b'00000000'
movwf 1dh
movlw b'00000010'
movwf 1eh
movlw b'00011100'
movwf 1fh
movlw b'01100000'
movwf 20h
movlw b'00110000'
movwf 21h
movlw b'00001110'
movwf 22h
movlw b'00000000'
movwf 23h
movlw b'00000000'
movwf 24h
movlw b'01111101'
movwf 25h
movlw b'00000000'
movwf 26h
movlw b'01111110'
movwf 27h
movlw b'00000100'
movwf 28h
movlw b'00000100'
movwf 29h
movlw b'01111000'
movwf 2ah
movlw b'00000000'
movwf 2bh
movlw b'00000000'
movwf 2ch
movlw b'00000000'
movwf 2dh
movlw b'00000000'
movwf 2eh
movlw b'00000000'
movwf 2fh
movlw b'00000000'
movwf 30h
movlw b'01000000'
movwf 31h
movlw b'01000100'
movwf 32h
movlw b'01111100'
movwf 33h
movlw b'01000000'
movwf 34h
movlw b'01000000'
movwf 35h
movlw b'00000000'
movwf 36h
movlw b'00000000'
movwf 37h
movlw b'01000100'
movwf 38h
movlw b'01010100'
movwf 39h
movlw b'01010100'
movwf 3ah
movlw b'01101100'
movwf 3bh
movlw b'00000000'
movwf 3ch
movlw b'00000000'
movwf 3dh
movlw b'01000100'
movwf 3eh
movlw b'01010100'
movwf 3fh
movlw b'01010100'
movwf 40h
movlw b'01101100'
movwf 41h
movlw b'00000000'
movwf 42h
movlw b'00000000'
movwf 43h
movlw b'00000000'
movwf 44h
movlw b'01000100'
movwf 45h
movlw b'00100100'
movwf 46h
movlw b'00011100'
movwf 47h
movlw b'00000100'
movwf 48h
movlw b'00000000'
movwf 49h
movlw b'00000000'
movwf 4ah
movlw b'00000000'
movwf 4bh

Restart movlw 10h ; Load 0x10 in P (first led combination)
movwf P
movlw 3Ch ; load 0x3C in C (0x3C=60 led combination)
movwf C

Start movf P,0 ; W = P
movwf FSR ; FSR = W
movf INDF,0 ; W = INDF (INDF is the value pointed by FSR)
movwf PORTB ; Display W on the led row
incf P,1 ; P++
call Delay ; wait a little bit
decfsz C,1 ; c--;if(C!=0){goto start} else {goto restart}
goto Start
goto Restart

Delay
Loop1 decfsz COUNT1,1 ; goto loop1 while COUNT1!=0
goto Loop1
return

end

Download this code: pov.asm

because i'm very lazy, i do not have typed all that byte sequence myself…
i wrote a tiny perl script who analyses a small picture (8px * 60px) and generate the byte sequence for me

picture:
Kevin 1337