Hello, I'm trying to build a midi controller, it is already working (in breadboard), but having much trouble with imprecision (values are not stable, keep changing). I'm next to give up, tried everything I know, which is not much so I asking (bothering) you to help me.

I tried to make a schematic (not good at this) so you can see what I done, I removed reset, power and some connections that will just keep schematics ugly, and its basic, its working so I think isnt them. I feeding all the circuit with 4 x 1.25v batteries (5v), all CD4051 IOs are connected to 10k pots, common output of CD4051 is connect to input of AD0804, midi output is connected to optocoupler, so, circuit is completly isolated.

Excuse me if I missed something (noob)




The code is very simple, it just reads ADC, verify if new value is different from old ram value, if yes, set ram value to new value and send midi data

WRA             EQU P3.4
INTR            EQU P3.5
RDA             EQU P3.3

TL              EQU 07Bh        ; Endereços das variaveis
TH              EQU 07Ch
TP              EQU 07Dh
V0              EQU 07Eh
V1              EQU 07Fh        ; DONT USE OVER THIS - SFR ADDRESS START


;P3.4 <-->WR(to start convert analog - binary (0804)we must have WR 0->1)
;P3.5 <-->INTR (=0 to and convert) 
;P3.3 <-->RD (RD 1->0 to read data from ADC)
;P2 <-->D0-D7 (out put) 
;-----------------------------------------------------------;

START:  MOV PCON,#0
        MOV TMOD,#00100010B ;Set Timer1 Mode for 8bit autoreload (T1M1=1)
        MOV TL1,#255        ;Set load/reload
        MOV TH1,#255        ;
        SETB TR1
        MOV SCON,#01000010B
        MOV P2,#255         ; to receive data from ADC
        MOV P1,#00000000b   ; Mux Input 0
        MOV R0,#080h
        MOV R2,#8
        MOV R3,#9
        
READ0:  CALL READ           ; Read ADC
        MOV P1,A
        CLR C               ; Midi adjust (MSB must be 0)
        RRC A               ; Midi adjust
        MOV TP,@R0
        CJNE A,TP,SEND0
        JMP INCI            ; EQUAL read next
SEND0:  MOV @R0,A
        CALL SEND
        
        
INCI:   MOV A,R3            ; INCREMENT FOR NEXT READ
        MOV R2,A            ; V
        MOV R0,A            ; V
        MOV A,#080h
        ORL A,R0
        MOV R0,A
        INC R3              ; V
        CJNE R3,#20,ISO     ; #N = NUMBER OF VALUES TO BE READ
        MOV R3,#8           ; V
ISO:    JMP READ0           ; START OVER




READ:   MOV P1,R2           ; Set mux Input
        MOV TL,#255
        MOV TH,#5
        CALL DELAY
        CLR WRA
        SETB WRA            ; dat WR = 1 to start convert
        JB INTR,$           ; wait to end convert 
        CLR RDA             ; end convert and allow read data from ADC
        MOV A,P2            ; read data onto A register
        MOV P1,R3           ; Set next input
        SETB RDA
        ;MOV P1,R3
        RET
        
SEND:   JNB TI,$            ; If diff send midi
        CLR TI
        MOV SBUF,#0B0H      ;Control Change Channel 0
        JNB TI,$
        CLR TI
        MOV SBUF,R2         ;Controller Number
        JNB TI,$
        CLR TI
        MOV SBUF,A          ;Controller Value
        RET
        
        




;------------------------------
Delay:  DJNZ TL,$
        MOV TL,#255
        DJNZ TH,Delay
        ;MOV TH,#255
        ;DJNZ TS,DTL
        RET


END

Thanks in advance (and for you patience).