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ADC 0844 errorneous results. Help me.

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Freddy

Mon Jul 28 2008, 11:37PM

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Hi everyone, I'm new in the forum. This is a good website.
Now, this my problem, the output of the ADC seems to give a weak output ( measured 1.1 V using multimeter). I would appreciate anyone helping

Problem Hints :
Hardware : AT89S51, ADC 0844 and 1x16 LCD
Case 1 : LCD displayed 00 when I include the line "acall clr_mux_add"
Case 2 : LCD displayed 05, 04, 00 (randomly )when I exclude the line "acall clr_mux_add"

Port 3.0 and 3.1 are connected to separated LEDs, so I can observed the program flow, that's all.

I programed the ADC based on the timing diagram given in the datasheet. (at the bottom of page)

From calculation, I should get 15 or 14 decimal displayed on my LCD, but I get 05 instead, I suspected this is because it displayed the MUX Address.
15 decimal = 0000 1111 b (but the 1's are measured to be 1.1 V)

Thanks for reading.

CODE:

WR_adc equ P3.5

RD_adc equ P3.7

DAT_ADC equ P2  ;ADC data pins P2

start :

acall clear_lcd        

                                          acall conv_adc

                                          acall read_adc

                                          acall byte_to_bcd

                                          acall write_text

                                          mov A, r0

                                          acall write_text

                                          setb P3.0

                                          acall delay_1sec         ;12

                                          clr P3.0             

                                          sjmp start

conv_adc :

           clr CS

           setb P3.1

           acall delay_500ms      ;1

           clr P3.1

           clr wr_adc

           setb P3.0

           acall delay_500ms     ;2

           clr P3.0

           nop

           acall mux_add ;set MA0-MA3 to 0101[using channel 2]

           setb P3.1

           acall delay_500ms      ;3

           clr P3.1

           nop

           setb wr_adc

           setb P3.0

           acall delay_500ms      ;4

           clr P3.0

           nop

           setb cs

           setb P3.1

           acall delay_500ms       ;5

           clr P3.1       

           acall clr_mux_add  

           acall delay_50us

           wait : jb intr_adc, wait

           setb P3.0

           acall delay_500ms             ;6

           clr P3.0

           ret

read_adc :

clr cs

                   setb P3.1

                   acall delay_500ms       ;7

                    clr P3.1

                   clr rd_adc

                   setb P3.0

                   acall delay_1sec        ;8

                   clr P3.0

                   nop

                   mov A, DAT_ADC  ;move ADC 8 bit result to A

                   ;mov adc_val, A

                   setb P3.1

                   acall delay_500ms       ;9

                   clr P3.1              

                  setb rd_adc

                   setb P3.0

                   acall delay_500ms       ;10

                   clr P3.0

                  nop

                  setb cs

                   setb P3.1

                   acall delay_500ms       ;11

                  clr P3.1

                   ret

mux_add :

 setb P2.0       ;this configuration is using channel 2 single ended

                  clr P2.1

                  setb p2.2

                  clr P2.3

                  ret

clr_mux_add :

clr P2.0

                          clr P2.1

                          clr P2.2

                          clr P2.3

                          ret

[ Edited Tue Jul 29 2008, 01:48AM ]

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Ajay

Tue Jul 29 2008, 08:17AM

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Posts: 3681
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try using interrupt..
you are wasting more time on making LEDs low high

so interrupt will solve your problem

www.rickeyworld.info
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Freddy

Freddy

Tue Jul 29 2008, 10:07AM

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Joined: Mon Jul 28 2008, 10:01PM

Posts: 37
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aaa, thanks for idea.... is there any other way ?

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Freddy

Tue Jul 29 2008, 12:32PM

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Joined: Mon Jul 28 2008, 10:01PM

Posts: 37
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Hi again, i've found the solution ( i think so) , all i did is add the highlighted line (compare with code above).

all thx to : http://www.8051projects.net/downloads84.html

because on page 59, i found this :

if it wasn't for Ajay, i wouldn't go hay-wire finding info about interrupts... hahaha , so thx Ajay.
now, the temperature displayed a more "make sense" value. Now i only use 0.5 sec of temperature sampling.

New problem :
The temperature reading is not so stable. It changes to different value too rapidly.
So, any engineering ideas are seriously welcomed !!

Build target 'Target 1''
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Arun Kumar V

Tue Jul 29 2008, 06:54PM

Registered Member #426

Joined: Sun Jan 28 2007, 11:50PM

Posts: 427
Thanked 178 times in 149 posts

hi freddy,

acall clear_lcd

why are you clearing the LCD every time in start loop ? if you are using two channels then one channel reading can be placed on line 1 and other channel data on line 2 of lcd.

if you are using only one ch, then you need not clear the LCD every time.

Arun

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Freddy

Freddy

Tue Jul 29 2008, 09:52PM

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Joined: Mon Jul 28 2008, 10:01PM

Posts: 37
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I only use 1 channel of the ADC.
When i remove the acall clear_lcd , the display would be continuous.
Something like this : 100F0F10

or maybe i understood u wrongly ??

Build target 'Target 1''
linking...
Program Size: data=8.0 xdata=0 code=709
creating hex file from "Final Year Project"...
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Arun Kumar V

Tue Jul 29 2008, 11:56PM

Registered Member #426

Joined: Sun Jan 28 2007, 11:50PM

Posts: 427
Thanked 178 times in 149 posts

Hi Freddy,

you have posted only part of the code, pl.post full code so that we can analyze other subroutines and find the error.

since you are using 1 ch and not switching between channels, it is not required to clear the LCD after every cycle.

Arun

Freddy

Wed Jul 30 2008, 03:09AM

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Joined: Mon Jul 28 2008, 10:01PM

Posts: 37
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owh okok, sorry about that. I'm just a beginner.

CODE:

;Information :

;the code is initilaise as 2x16 although it is 1x16 

;because of the 8+8 configuration.

;the ninth position start at the address 40h

;[00 01 02 03 04 05 06 07 41 42 43 44 45 46 47]

;#07h --> shift display to the left

ORG 0000H

mov P0, #00h

mov P1, #00h

mov P2, #00h

mov P3, #00h

MOV TMOD, #0x01

RS_lcd EQU P1.2

RW_lcd EQU P1.1

EN_lcd EQU P1.0

DAT_lcd EQU P0          ;LCD PORT for DB0 to DB7

INTR_adc equ P3.4

WR_adc equ P3.5

CS_adc equ P3.6

RD_adc equ P3.7

DAT_ADC equ P2          ;ADC data pins P2

mux_add equ 30h

aCALL INIT_LCD

setb P3.5

clr P3.6

setb P3.7

mov mux_add, #00000101b ;channel 2, single-ended mode

;==============================================================

disp_str macro string           ;Macro for sending string to LCD

                 irpc char, <string>

                 if nul 'char'

                 exitm

                 endif

                 mov a,#'char'

                 lcall write_text

                 endm

                 endm

start :

acall clear_lcd

acall conv_adc

disp_str <Temp:>

mov dat_lcd, #85h       ;80h + 05h (instruction + lcd mapping address)

setb en_lcd

acall delay_2ms

clr en_lcd

mov P2, 0xFF            ;configure to read from port 2

acall read_adc

acall byte_to_bcd              

acall write_text   ;display upper nibble

mov A, r0            ;display lower nibble

acall write_text

acall delay_500ms       

sjmp start

conv_adc :

clr wr_adc

nop

mov dat_adc, mux_add ;load mux address into A

nop

setb wr_adc

wait : jb intr_adc, wait             

ret

read_adc :

clr rd_adc

nop

mov A, DAT_ADC  ;move ADC 8 bit result to A

nop

setb rd_adc

nop

ret

;==========================================================

;this subroutine converts 8-bit data to bcd

;both high nibble and low nibble are in hex value

;input is taken from A

;the output high nibble is A (hex value)

;the output low nibble is in r0 (also hex value)

byte_to_bcd:

    MOV     R0,A

    ANL     A,#0Fh

    ADD     A,#0F6h

    JNC     byte_to_bcd_2

    ADD     A,#07h

byte_to_bcd_2:

    ADD     A,#3Ah

    XCH     A,R0

    SWAP    A

    ANL     A,#0Fh

    ADD     A,#0F6h

    JNC     byte_to_bcd_3

    ADD     A,#07h

byte_to_bcd_3:

    ADD     A,#3Ah

    RET 

;===========================================================

WAIT_LCD :  

acall DELAY_2ms                

RET

INIT_LCD :  

clr en_lcd

CLR RS_lcd

clr rw_lcd

MOV DAT_lcd, #38h  ;initialize lcd as 2x16                        

SETB EN_lcd

acall DELAY_2ms

CLR EN_lcd

aCALL WAIT_LCD

clr en_lcd

CLR RS_lcd

clr rw_lcd

MOV DAT_lcd,#0Ch        ;no cursor, no blinking of cursor                 

SETB EN_lcd

acall DELAY_2ms

CLR EN_lcd

aCALL WAIT_LCD

clr en_lcd

CLR RS_lcd

clr rw_lcd

MOV DAT_lcd,#06h                       

SETB EN_lcd

acall DELAY_2ms

CLR EN_lcd

aCALL WAIT_LCD

clr en_lcd

CLR RS_lcd

clr rw_lcd

MOV DAT_lcd,#14h

SETB EN_lcd

acall DELAY_2ms

CLR EN_lcd

aCALL WAIT_LCD

RET

CLEAR_LCD :     

clr en_lcd

CLR RS_lcd

clr rw_lcd

MOV DAT_lcd,#01h                       

SETB EN_lcd

acall DELAY_2ms

CLR EN_lcd

aCALL WAIT_LCD

RET

WRITE_TEXT :

clr en_lcd

SETB RS_lcd

clr rw_lcd

 MOV DAT_lcd, A                  

SETB EN_lcd

 acall DELAY_2ms

CLR EN_lcd

aCALL WAIT_LCD

RET

;===========================================================================

;Delay subroutines...

DELAY_50us: MOV R5, #1          ;this is a 50 micro second delay subroutine       

REPEAT_4:MOV TH0, #0xFF

                MOV TL0, #0xD2

                SETB TR0

BACK_4: JNB TF0, BACK_4

                CLR TR0

                CLR TF0

                DJNZ R5, REPEAT_4

                RET

DELAY_33ms: MOV R5, #100                ;this is a 33 mili second delay subroutine        

REPEAT_3:MOV TH0, #0xFE

                MOV TL0, #0xCF

                SETB TR0

BACK_3:  NB TF0, BACK_3

                 CLR TR0

                CLR TF0

                DJNZ R5, REPEAT_3

                RET

DELAY_2ms:  MOV R5, #100                ;this is a 2ms delay subroutine   

REPEAT: MOV TH0, #0xFF

                MOV TL0, #0xEE

                SETB TR0

BACK:   JNB TF0, BACK

                CLR TR0

                CLR TF0

                DJNZ R5, REPEAT

                RET

DELAY_500ms: MOV r5, #100               ;this is a 0.5 second delay subroutine    

REPEAT_2:MOV TH0, #0xEE

                MOV TL0, #0x00

                SETB TR0

BACK_2: JNB TF0, BACK_2

                CLR TR0

                CLR TF0

                DJNZ r5, REPEAT_2

                RET

DELAY_1sec: MOV R5, #100                ;this is a 1 second delay subroutine      

REPEAT_1:MOV TH0, #0xD8

                MOV TL0, #0xF0

                SETB TR0

BACK_1: JNB TF0, BACK_1

                CLR TR0

                CLR TF0

                DJNZ R5, REPEAT_1

                RET                                                    

END

Build target 'Target 1''
linking...
Program Size: data=8.0 xdata=0 code=709
creating hex file from "Final Year Project"...
"Final Year Project" - 0 Error(s), 0 Warning(s).

Arun Kumar V

Wed Jul 30 2008, 07:30AM

Registered Member #426

Joined: Sun Jan 28 2007, 11:50PM

Posts: 427
Thanked 178 times in 149 posts

Hi Freddy,

first things first :

mov P0, #00h
mov P1, #00h
mov P2, #00h
mov P3, #00h

this is a big No-No, on reset all the ports are 0FFh by default so lets keep it that way.

in subroutine byte_to_bcd:

ADD A,#3Ah

it should be #30H ( since you are converting into Ascii for sending it to LCD), also i doubt if this routine is right, bcoz to display FFh you need 3 digits in BCD i,e 255 but you are displaying only 2 digits ( A & R0)

you can use the following routine, which converts 1 byte Hex to 3 digit decimal ( you need to declare the variables - hundreds, tens & ones):

CODE:

Bin2Dec:

       mov b,#100d

       div ab

       mov hundreds,a

       mov a,b

       mov b,#10d

       div ab

       mov tens,a

       mov ones,b

       ret

and when dispatching to LCD, just add or ORL #30h to hunds, tens & ones

in the DELAY_1sec rountine,

MOV TH0, #0xD8
MOV TL0, #0xF0

the timer reload values are wrong, you haven't mentioned the xtal Freq but i guess you are using 11.0592Mhz

it should be :

CODE:

MOV TH0,#0DCH  ;  10mSec X 100(R5)  = 1000mS

                      MOV TL0,#00H

make these changes and check if the LCD displays correctly

PS: i hope the interfacing sequence to the ADC is correct ( write/read ).

All the Best !

Arun

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Freddy

Freddy

Wed Jul 30 2008, 10:20PM

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Joined: Mon Jul 28 2008, 10:01PM

Posts: 37
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wow Arun, now I can display the results in decimal value instead of hex. Thanks
I recalculate the formula, I still think that my 1 second delay is correct. I'm using 11.0592 MHz

100 x (65536-55536) x 1.085 us = 1.085 sec ( approx. 1 sec)
(1/11.0592 Mhz) / 12 = 921,600 Hz
1 / 921,600 = 1.085 us
D8F0h = 55536

Now, my problem is :
The temperature reading is fluctuating from 14-18 at room temperature ( i set Vref of ADC to Vcc=4.9 V). From calculation, I should get 15 or 16.

I suspected this is because of I didn't have any signal conditioning circuit for the ADC analog input. Can this be the problem ??

Vin is from LM35 temp sensor = 0.29 V
stepsize for ADC = 4.90 V / 256 = 19 mV
Dout is in decimal
0.29 / 19mV = 15.263

CODE:

;Information :

;the code is initilaise as 2x16 although it is 1x16 

;because of the 8+8 configuration.

;the ninth position start at the address 40h

;[00 01 02 03 04 05 06 07 41 42 43 44 45 46 47]

;#07h --> shift display to the left

ORG 0000H

MOV TMOD, #0x01

RS_lcd EQU P1.2

RW_lcd EQU P1.1

EN_lcd EQU P1.0

DAT_lcd EQU P0          ;LCD PORT for DB0 to DB7

INTR_adc equ P3.4

WR_adc equ P3.5

CS_adc equ P3.6

RD_adc equ P3.7

DAT_ADC equ P2          ;ADC data pins P2

mux_add equ 30h

hundreds equ 31h

tens equ 32h

ones equ 33h

aCALL INIT_LCD

setb P3.5  ;initialize wr_adc high

clr P3.6   ;set cs_adc always low

setb P3.7  ;initialize rd_adc high

clr P3.0 ;off LED connected to P3.0

clr P3.1  ;off LED connected to P3.1

mov mux_add, #00000101b ;MUX address for ADC0844

                                                ;channel 2, single-ended mode

;==============================================================

disp_str macro string           ;Macro for sending string to LCD

                 irpc char, <string>

                 if nul 'char'

                 exitm

                 endif

                 mov a,#'char'

                 lcall write_text

                 endm

                 endm

start : acall clear_lcd

                acall conv_adc

                disp_str <Temp:>

                mov P2, 0xFF            ;configure to read from port 2

                acall read_adc

                acall bin2dec

                acall ascii4lcd_tens           

                acall write_text   ;write tens to LCD

                acall ascii4lcd_ones     

                acall write_text   ;write ones to LCD

                clr en_lcd

                clr rs_lcd

                clr rw_lcd

                mov dat_lcd, #0C0h ;80h + 40h (instruction + lcd mapping address)

                setb en_lcd

                acall delay_2ms

                clr en_lcd

                acall wait_lcd

                disp_str <Celcius>

                acall delay_500ms       

                sjmp start

;====================================================

Bin2Dec:

       mov b,#100d ;1100 0100

       div ab

       mov hundreds,a

       mov a,b

       mov b,#10d

       div ab

       mov tens,a

       mov ones,b

       ret

;=============================================

ascii4lcd_tens :

add A, #30h     ;add 30h to tens value

ret

ascii4lcd_ones :

mov A, B

add A, #30h

ret

;=========================================================

conv_adc :

           clr wr_adc

           nop

           mov dat_adc, mux_add ;load mux address into A

           nop

           setb wr_adc

           wait : jb intr_adc, wait         

           ret

read_adc : clr rd_adc

                   nop             

                   mov A, DAT_ADC  ;move ADC 8 bit result to A

                   nop

               setb rd_adc

               nop

               ret

;==========================================================

;===========================================================

WAIT_LCD :  acall DELAY_2ms            

            RET

INIT_LCD :  clr en_lcd

                        CLR RS_lcd

                        clr rw_lcd

                MOV DAT_lcd, #38h  ;initialize lcd as 2x16                        

                SETB EN_lcd

                        acall DELAY_2ms

                        CLR EN_lcd

                aCALL WAIT_LCD

                        clr en_lcd

                CLR RS_lcd

                        clr rw_lcd

                MOV DAT_lcd,#0Ch        ;no cursor, no blinking of cursor                 

                SETB EN_lcd

                        acall DELAY_2ms

                CLR EN_lcd

                aCALL WAIT_LCD

                        clr en_lcd

                CLR RS_lcd

                clr rw_lcd

                        MOV DAT_lcd,#06h                       

                SETB EN_lcd

                        acall DELAY_2ms

                CLR EN_lcd

                aCALL WAIT_LCD

                        clr en_lcd

                    CLR RS_lcd

                        clr rw_lcd

                MOV DAT_lcd,#14h

                        SETB EN_lcd

                        acall DELAY_2ms

                CLR EN_lcd

                aCALL WAIT_LCD

                        RET

CLEAR_LCD :     clr en_lcd

                        CLR RS_lcd

                        clr rw_lcd

                MOV DAT_lcd,#01h                       

                SETB EN_lcd

                        acall DELAY_2ms

                CLR EN_lcd

                aCALL WAIT_LCD

                RET

WRITE_TEXT : clr en_lcd

                         SETB RS_lcd

                 clr rw_lcd

                         MOV DAT_lcd, A                  

                 SETB EN_lcd

                         acall DELAY_2ms

                 CLR EN_lcd

                 aCALL WAIT_LCD

                 RET

;===========================================================================

;Delay subroutines...

DELAY_50us: MOV R5, #1          ;this is a 50 micro second delay subroutine       

REPEAT_4:       MOV TH0, #0xFF

                        MOV TL0, #0xD2

                        SETB TR0

BACK_4:         JNB TF0, BACK_4

                        CLR TR0

                        CLR TF0

                        DJNZ R5, REPEAT_4

                        RET

DELAY_33ms: MOV R5, #100                ;this is a 33 mili second delay subroutine        

REPEAT_3:       MOV TH0, #0xFE

                        MOV TL0, #0xCF

                        SETB TR0

BACK_3:         JNB TF0, BACK_3

                        CLR TR0

                        CLR TF0

                        DJNZ R5, REPEAT_3

                        RET

DELAY_2ms:  MOV R5, #100                ;this is a 2ms delay subroutine   

REPEAT:         MOV TH0, #0xFF

                        MOV TL0, #0xEE

                        SETB TR0

BACK:           JNB TF0, BACK

                        CLR TR0

                        CLR TF0

                        DJNZ R5, REPEAT

                        RET

DELAY_500ms: MOV r5, #100               ;this is a 0.5 second delay subroutine    

REPEAT_2:       MOV TH0, #0xEE

                        MOV TL0, #0x00

                        SETB TR0

BACK_2:         JNB TF0, BACK_2

                        CLR TR0

                        CLR TF0

                        DJNZ r5, REPEAT_2

                        RET

DELAY_1sec: MOV R5, #100                ;this is a 1 second delay subroutine      

REPEAT_1:       MOV TH0, #0xD8

                        MOV TL0, #0xF0

                        SETB TR0

BACK_1:         JNB TF0, BACK_1

                        CLR TR0

                        CLR TF0

                        DJNZ R5, REPEAT_1

                        RET                                                    

END

Build target 'Target 1''
linking...
Program Size: data=8.0 xdata=0 code=709
creating hex file from "Final Year Project"...
"Final Year Project" - 0 Error(s), 0 Warning(s).