ADC- does an op-amp provide enough current to perfom ADC with a PIC.

edofbrighton · Feb 14, 2011

The ADC i'm using doesn't convert the voltage i put on to it, can anyone explain why? The voltage is obtained from a series of op-amps used to get the output from a bridge. It's designed correectly. If i connect a vm across it, it gives the right voltage, but when i use the pic to digitlise it i get a voltage of zero. I wonder if this is because the current supllied by the op-amp is to small too charge the capacitor in the sample and hold for the pic. The ADC works if i connect it to the supply rail to it. Does anyone has any experience of similar problems?

circuit:

bridge-two buffer(voltage follower op-amps)-diferential op-amp-lowpass filter-final buffer (another voltage follower).

cheers,
ed.

blueroomelectronics · Feb 14, 2011

Part numbers? Proper schematic?

MikeMl · Feb 14, 2011

Post your schematic.

edofbrighton · Feb 14, 2011

Sorry, i didn't have any tools to draw it with. Here it is. I think the r=1.2k and c=1uf for filter, not certain though.

edofbrighton · Feb 14, 2011

didin't attach first time

edofbrighton · Feb 14, 2011

I'm using two different op-amps:
AD8031
and LM741CN

blueroomelectronics · Feb 14, 2011

What's the power supply rated at?
Untitled Document

edofbrighton · Feb 14, 2011

+ve=5v and -ve=0V

blueroomelectronics · Feb 14, 2011

You need a split supply for that circuit. The 741 needs at least +/- 10V

edofbrighton · Feb 14, 2011

That might be difficult. Do you think it would work if i change the LM741s?

Reloadron · Feb 14, 2011

If you really want to amplify the output of a bridge (like a strain gauge or similar) you may want to look at (Google) instrumentation amplifiers which are designed for what you want to do. You will also in most cases need a split power supply as was covered.

Just My Take
Ron

MikeMl · Feb 14, 2011

Only a modern, rail-to-rail INPUT, rail-to-rail OUTPUT OpAmp will amplify a signal so that it ranges from near 0V to near 5V while the opamp itself is powered from Vdd Pin=5V and Vss Pin=0V.

To get a 0V to 5V signal to fill the full dynamic range of a PIC's ADC, you would have to power a crummy 741 from Vdd=+10V and Vss = -10V. I suspect that your INA is likely not properly powered either.

Hand draw you schematic, and take a picture of it with a digital camera if you dont have a scanner.

edofbrighton · Feb 18, 2011

hi again,

I tired the circuit with the new op-amp and i'm still noy having any success. It's the same problem as before, the circuit works, but only until it is connected to the ADC. suggestions on for to fix this problem would be very much appricated. Please see the new schematic.

thanks,
ed.

I should also say that the maximum input impedance to the ADC is 10K.

edofbrighton · Feb 18, 2011

this a link to the data sheet: https://www.electro-tech-online.com/custompdfs/2011/02/AD8031_8032.pdf

Sig239 · Feb 18, 2011

If you're getting the correct voltage out of the op-amp circuit, then perhaps the ADC is not configured properly on the PIC.

Post your code.

Also, what are you using for a voltage reference?

Edit: When you say it quits working when hooked up to the adc, I assume you just mean that you're not getting the expected results from the pic. Is that correct? Have you measured the output of the op-amp circuit using a voltmeter, while also hooked up to the pic?

audioguru · Feb 18, 2011

The 741 opamp is 43 years old and has very poor spec's today. Only teachers use it anymore.

It looks like you need a modern intrumentation amplifier IC that has very well-matched resistors and opamps.

edofbrighton · Feb 18, 2011

Sig239,
Before I connect the amplifer its output is approximately 2.5V, but when i connect it to the adc it falls to around 0.7V. Since i changed all three op-amps to ad8031's it performancre is better. The voltage does vary when the FSR is pressed (it goes from 0.7V to 0.3V), but i think the pin voltage should be 2.5V?

The ADC i'm using appears to working, but not properly. If i connect the 5V rail i get a reading, and other voltages also give me a reading, but not an accurate one; I designed my program to display the decimal value in each register adresh and adresl, but appears to display adresh twice. Example: when i connect 5V i get 003 0003, and for 2.5V i get 001 001. Even if i could convert the voltage from the amplifier i would know it because it would not se any bits in adresh.

audioguru,

I am not using the 741 anymore, just ad3081's. The voltage reference is just the power supply to the PIC 5V.

blueroomelectronics · Feb 18, 2011

Add a unity gain follower. Are you using the PICs ADC or an external one?

edofbrighton · Feb 18, 2011

I using the pic adc. I will try adding a voltage follower.

Just on thought. The data shet said on page 15, that the op-amp may struggle with purely capacitive loads. Could this be the problem?

edofbrighton · Feb 18, 2011

my code if anyone is interested.

Code:

#include <p16F690.inc>
    __config (_INTRC_OSC_NOCLKOUT& _WDT_OFF & _PWRTE_OFF & _MCLRE_OFF & _CP_OFF & _BOR_OFF & _IESO_OFF & _FCMEN_OFF)
	


;----------------------------------------
; DELAY EQUATES
CNT          	  EQU 0X25         ;ADDRESS FOR COUNTER
CNT2          	  EQU 0X26         ;ADDRESS FOR COUNTER2
CNT3          	  EQU 0X27         ;ADDRESS FOR COUNTER3
RECEIVEDBYTE      EQU 0X28         ;ADDRESS FOR COUNTER4
BREATH_ADC0	  	  EQU 0X29		   ;ADDRESS FOR RECEIVED BIT
BREATH_ADC1   	  EQU 0X2A
NUMBER_OF_BREATHS EQU 0X2B
CNT5																																																																																			  	  EQU 0X2C
BINARY		      EQU 0X2D
t1				  EQU 0X2E
w2			 	  EQU 0X2F
COUNTER 		  EQU 0X30
TEMP			  EQU 0X31
D1				  EQU 0X32
D0				  EQU 0X33
SAMPLEREG		  EQU 0X34
D2				  EQU 0X35
D3				  EQU 0X36
SAMPLEOLD 		  EQU 0X37
SAMPLENEW 		  EQU 0X38
D4				  EQU 0X39
D5				  EQU 0X3A
D6				  EQU 0X3B
SAMPLEOLDLOW	  EQU 0X3C
SAMPLEOLDHIGH	  EQU 0X3D
SAMPLENEWLOW	  EQU 0X3E
SAMPLENEWHIGH	  EQU 0X3F
W_Save			  EQU 0X40
STATUS_Save		  EQU 0X41
TOTALBREATHS	  EQU 0X42
SAMPLE1			  EQU 0X43
SAMPLE2			  EQU 0X44
SAMPLE3			  EQU 0X45
SAMPLE4			  EQU 0X46
SAMPLE5			  EQU 0X47
SAMPLE6			  EQU 0X48
SAMPLE7			  EQU 0X49
SAMPLE8			  EQU 0X50
SAMPLE9			  EQU 0X51
SAMPLE10		  EQU 0X52
SAMPLE11		  EQU 0X53
SAMPLE12		  EQU 0X54
TIMERCOUNTER	  EQU 0X55
TOTALNOB		  EQU 0X56
D7				  EQU 0X57
D8				  EQU 0X58
D9				  EQU 0X59
D10				  EQU 0X5A
ONES			  EQU 0X5B
TENS			  EQU 0X5C
HUNDEREDS		  EQU 0X5D


; LCD EQUATES AND DEFINES
#DEFINE     DDRE   TRISB,7     ;DATA DIRECTION
#DEFINE     DDRRS  TRISB,4     ;DATA DIRECTION
#DEFINE     E      PORTA,2     ;ENABLE LINE ON LCD
#DEFINE     RS     PORTB,4     ;INSTRUCTION/DATA SELECT
#DEFINE 	RW	   PORTB,6
TEMP_LCD    EQU 0X3A           ;STORAGE FOR LCD
LCD         EQU PORTC          ;LCD DATA PORT
CLRSCR      EQU B'00000001'    ;COMMAND FOR CLRSCR
HOME        EQU B'00000010'    ;SENDS CURSOR TO HOME
ON          EQU B'00001100'    ;TURNS ON THE DISPLAY
OFF         EQU B'00001000'    ;TURNS THE DISPLAY OFF
LEFT        EQU B'00011000'    ;LEFT SHIFT
RIGHT       EQU B'00011100'    ;RIGHT SHIFT
LIN2        EQU B'11000000'    ;SETS TO LINE 2
TIMERCOMP	EQU	D'4'

;----------------------------------------
	; VECTOR FOR NORMAL START UP.
        ORG     0
        GOTO    START
;--------------------------------------------
;INTERRUPT ROUTINE 
;--------------------------------------------
NOP
NOP
NOP
ISR:
movwf     W_Save				;SAVES STATUS REGISTER 
movf      STATUS,w
movwf     STATUS_Save
BTFSS	  PIR1,TMR1IF			
GOTO	  $-1
bcf		  PIR1,TMR1IF
INCF	  TIMERCOUNTER
MOVFW 	  TIMERCOUNTER 		    ;STORE NEW SAMPLE AND SUBTRACT IT FROM OLD
SUBLW	  D'10'
BTFSC	  STATUS,Z 
CALL      DISPLAYBREATHINGRATE 
MOVLW	  B'11011100'
MOVWF 	  TMR1L
MOVLW 	  B'00001011'
MOVWF	  TMR1H
movf      STATUS_Save,w
movwf     STATUS
swapf     W_Save,f
swapf     W_Save,w
retfie
;-----------------------------------------------
; MAIN PROGRAM STARTS HERE:
;----------------------------------------------
START:
CLRW					; CLEAR W.	
MOVWF   PORTA           ; ENSURE PORTA IS ZERO BEFORE WE ENABLE IT.
MOVWF   PORTB           ; ENSURE PORTB IS ZERO BEFORE WE ENABLE IT.
MOVWF 	PORTC

BSF     STATUS,RP1
MOVLW	H'00'
MOVWF 	ANSEL
MOVLW	B'00000010'		;DIGITAL/ANALOGUE SETS AN9 AS ANANLOGUE 
MOVWF 	ANSELH

BCF     STATUS,RP1
BSF     STATUS,RP0      ; SELECT BANK 1

;MOVLW	B'0000100'		; SETS CLOCK TO BE RUN FROM EXTERNAL OSC. DEFINED IN CONFIG BITS. PAY ATENTION TO BITS 0 AND 3 FOR REPORT
;MOVWF	OSCCON

MOVLW   H'00'           ; ALL PORTA OUTPUTS
MOVWF   TRISA           ; SET TRISA REGISTER.

MOVLW   B'00100000'     ; SET B5 RX PIN AS INPUT 
MOVWF   TRISB           ; SET TRISB REGISTER.

MOVLW	H'00000000'		;ALL OF PORTC OUTPUTS 
MOVWF	TRISC

MOVLW   b'01100000'           ; A2D Clock Fosc/8 4MHz CLOCK
MOVWF   ADCON1 	

BCF     STATUS,RP0      ; RESELECT BANK 0.

MOVLW	B'10100101'		; ADCON0 . ADCON 0 BIT 7=0 LJ. BIT 6=0 VDD REF. BITS 5-2 1011 SEL AN11. BIT 1 GO/DONE BIT. BIT0=1 ENABLE IT.
MOVWF	ADCON0


CALL	UART_SETUP		
;CALL	INIT_LCD		; Initialse the LCD
;CALL    CLEARSCREEN	 	;Clear the screen
;CALL	LETTER
CALL	DISPLAYADC0EDIT1


CALL	UART_SETUP
JOE:
BSF		RCSTA,SPEN
MOVLW	'B'
CALL	SEND
MOVLW	'R'
CALL	SEND
MOVLW	'A'
CALL	SEND
MOVLW	'P'
CALL	SEND
MOVLW	'A'
CALL	SEND
BCF		RCSTA,SPEN
BCF		PORTB,7
CALL	SECOND
GOTO	JOE

DISPLAYADC0EDIT1:
MOVLW	  D'255'				;MOVES 255 TO OLD SAMPLE LOW AND HIGH BYTES
MOVWF	  SAMPLEOLDLOW			
MOVWF	  SAMPLEOLDHIGH
CLRF	  NUMBER_OF_BREATHS		;CLEARS NUMBER OF BREATHS 
CLRF	  TOTALNOB  			;CLEARS TOTAL NUMBER OF BREATHS 
DISPLAYADCEDIT1:
BSF       ADCON0,GO      		; STARTS ADC CONVERSION
BTFSS     ADCON0,GO      		; POLLING WHEN TO SEE WHEN ADC HAS BEEN COMPLETE
GOTO      $-1
MOVFW 	  ADRESH				;MOVES HIGH BYTE OF ADC TO SAMPLE HIGH 
MOVWF	  SAMPLENEWHIGH			
MOVFW	  ADRESL				;MOVES LOW BYTE OF ADC TO SAMPLE LOW
MOVWF	  SAMPLENEWLOW 
;CALL	  LARGECOMPAREOLDGTNEW 	;COMPARES THE LAST ADC SAMPLE TO NEW ADC SAMPLE. IF THE NEW IS GREATER THAN THE OLD SAMPLEREG BIT 0 IS SET.
;BTFSC	  SAMPLEREG,0
;INCF	  NUMBER_OF_BREATHS
MOVLW	  'B'
CALL	  SEND
;MOVFW	  NUMBER_OF_BREATHS
MOVFW	  SAMPLENEWHIGH
CALL	  GETHNDS
CALL 	  LOOKUP_TABLE 
MOVWF 	  SAMPLE1
CALL 	  SEND 
;MOVFW	  NUMBER_OF_BREATHS
MOVFW	  SAMPLENEWHIGH
CALL	  GETTENS
CALL 	  LOOKUP_TABLE 
MOVWF 	  SAMPLE2
CALL 	  SEND 
;MOVFW	  NUMBER_OF_BREATHS
MOVFW	  SAMPLENEWHIGH
CALL	  GETONES
CALL 	  LOOKUP_TABLE 
MOVWF 	  SAMPLE3
CALL 	  SEND 
;MOVFW	  NUMBER_OF_BREATHS
MOVFW	  SAMPLENEWLOW
CALL	  GETHNDS
CALL 	  LOOKUP_TABLE 
MOVWF 	  SAMPLE4
CALL 	  SEND 
;MOVFW	  NUMBER_OF_BREATHS
MOVFW	  SAMPLENEWLOW
CALL	  GETTENS
CALL 	  LOOKUP_TABLE 
MOVWF 	  SAMPLE5
CALL 	  SEND 
;MOVFW	  NUMBER_OF_BREATHS
MOVFW	  SAMPLENEWLOW
CALL	  GETONES
CALL 	  LOOKUP_TABLE 
MOVWF 	  SAMPLE6
CALL 	  SEND 
CALL	  SECOND
GOTO	  DISPLAYADCEDIT1


	
CALL	INTERRUPTSETUP
CALL	DISPLAYADC0EDIT 

ROWANISGAY:

MOVLW	'H'
CALL   	SEND 
MOVLW 	'E'
CALL	SEND 
MOVLW	'L'
CALL 	SEND
MOVLW	'L'
CALL	SEND
MOVLW	'O'
CALL	SEND
CALL	TENSECONDS

GOTO	ROWANISGAY


;---------------------------------------------------
;DISPLAYS BREATHING RATE 
;---------------------------------------------------

DISPLAYBREATHINGRATE:
MOVLW     CLRSCR				
CALL      COMMAND
MOVFW	  NUMBER_OF_BREATHS 
ADDWF	  TOTALNOB
MOVFW	  TOTALNOB
CALL	  DISPLAYBCD

MOVLW	  'B'
CALL	  DISPLAY
MOVLW	  'R'
CALL	  DISPLAY
MOVLW	  ':'
CALL	  DISPLAY
CLRF	  TIMERCOUNTER
CLRF	  TOTALBREATHS
MOVFW	  SAMPLE11
MOVWF	  SAMPLE12
ADDWF 	  TOTALBREATHS
MOVFW	  SAMPLE10
MOVWF	  SAMPLE11
ADDWF 	  TOTALBREATHS
MOVFW	  SAMPLE9
MOVWF	  SAMPLE10
ADDWF 	  TOTALBREATHS
MOVFW	  SAMPLE8
MOVWF	  SAMPLE9
ADDWF 	  TOTALBREATHS
MOVFW	  SAMPLE7
MOVWF	  SAMPLE8
ADDWF 	  TOTALBREATHS
MOVFW	  SAMPLE6
MOVWF	  SAMPLE7
ADDWF 	  TOTALBREATHS
MOVFW	  SAMPLE5
MOVWF	  SAMPLE6
ADDWF 	  TOTALBREATHS 
MOVFW	  SAMPLE4
MOVWF	  SAMPLE5
ADDWF 	  TOTALBREATHS
MOVFW	  SAMPLE3
MOVWF	  SAMPLE4
ADDWF 	  TOTALBREATHS
MOVFW	  SAMPLE2
MOVWF	  SAMPLE3
ADDWF 	  TOTALBREATHS 
MOVFW	  SAMPLE1
MOVWF	  SAMPLE2
ADDWF	  TOTALBREATHS
MOVFW 	  NUMBER_OF_BREATHS
MOVWF	  SAMPLE1
ADDWF	  TOTALBREATHS
CLRF	  NUMBER_OF_BREATHS
MOVFW 	  TOTALBREATHS 	
CALL	  DISPLAYBCD
MOVLW	  ' '
CALL	  DISPLAY
MOVLW	  'b'
CALL	  DISPLAY
MOVLW	  'p'
CALL	  DISPLAY
MOVLW	  'm'
CALL	  DISPLAY

RETURN
;----------------------------------------------------
;FINDS ASCII EQUIVILENT FOR VAULE IN W
;----------------------------------------------------
	 	
LOOKUP_TABLE:

ANDLW     B'00001111'	;STOP VALUE GOING BEYOND TABLE RANGE 
ADDWF	  PCL	
RETLW 	  '0'	               
RETLW	  '1'
RETLW	  '2'
RETLW 	  '3'
RETLW	  '4'
RETLW 	  '5'
RETLW     '6'
RETLW 	  '7'
RETLW	  '8'
RETLW	  '9'
;----------------------------------------------------------------------------------------------
;-INCREAMENTS NUMBER OF BREATHS IF CHANGE OF DIRECTION IN VOLTAGE HAS OCCURRED. CHECK WHICH WAY
;-----------------------------------------------------------------------------------------------
INCFNOB:
BTFSC	 SAMPLEREG,1		;SKIPS IF BIT 1 OF SAMPLE REG IS SET. IF IT IS NOT NOB IS INCREMENTED 
INCF 	 NUMBER_OF_BREATHS 	
BSF		 SAMPLEREG,1		;SETS BIT 1 OF SAMPLE REG.
RETURN
	
;----------------------------------------------------------------------------------------------
;8-BIT COMPARE FOR ADC SAMPLES
;---------------------------------------------------------------------------------------------
SAMPLEOLD_GT_SAMPLENEW:
BTFSC	SAMPLEREG,1			;IF THIS BIT IS SET MEANS THAT THERE HAS BEEN A CHANGE IN VOLTAGE DIRECTION 
GOTO	INCFNOB
MOVFW	ADRESH
INCF	W					;NEEDS TO BE INCREMENTED SO CARRY FLAG DOESN'T SET WHEN THEY ARE EQUAL 
MOVFW	SAMPLENEW
SUBWF 	SAMPLEOLD  
BTFSS	STATUS,C
BCF 	SAMPLEREG,0 		;IF NEW SAMPLE IS GREATER THAN OLD THIS WILL BE CLEAR
MOVFW 	SAMPLENEW
MOVWF 	SAMPLEOLD
RETURN  



DISPLAYADC0:
MOVLW	  D'255'
MOVWF	  SAMPLEOLDLOW
MOVWF	  SAMPLEOLDHIGH
CLRF	  NUMBER_OF_BREATHS 
DISPLAYADC:
BSF       ADCON0,GO      ; start conversion
BTFSS     ADCON0,GO      ; this bit will change to zero when the conversion is complete
GOTO      $-1
MOVFW 	  ADRESH
MOVWF	  SAMPLENEWHIGH
MOVFW	  ADRESL
MOVWF	  SAMPLENEWLOW 
CALL	  LARGECOMPAREOLDGTNEW 
BTFSC	  SAMPLEREG,0
CALL	  INCFNOB
MOVFW	  NUMBER_OF_BREATHS
CALL 	  DISPLAYBCD 
;CALL 	  TENTH_SEC_DELAY 
MOVLW     CLRSCR		; Clear the screen
CALL      COMMAND
MOVFW	  SAMPLENEWHIGH
MOVWF	  SAMPLEOLDHIGH
MOVFW	  SAMPLENEWLOW
MOVWF	  SAMPLEOLDLOW

GOTO 	  DISPLAYADC

;-------------------------------------------------------------------------------------------------------
;COUNTS THE NUMBER OF BREATHS TAKEN UNTIL IT IS INTERRUPTED. TIMER1 INTERRUPTS PROGRAM EVERY 0.5 SECONDS


ADCTRIAL

BSF       ADCON0,GO      ; start conversion
BTFSS     ADCON0,GO      ; this bit will change to zero when the conversion is complete
GOTO      $-1
MOVFW 	  ADRESH 
MOVWF 	  SAMPLENEW
;CALL	  SAMPLENEW_GT_SAMPLEOLD
BTFSS	  SAMPLEREG,0
INCF 	  NUMBER_OF_BREATHS
MOVLW     CLRSCR		; Clear the screen
MOVFW	  NUMBER_OF_BREATHS
CALL      COMMAND	 
CALL 	  DISPLAYBCD
;CALL 	  TENTH_SEC_DELAY
GOTO	  ADCTRIAL 

RETURN

;--------------------------------------------------
;DISPLAYS BCD FOR VALUE CONTAINED IN W
;--------------------------------------------------
DISPLAYBCD:
MOVWF 	BINARY 
CALL 	GETHNDS 
CALL 	LOOKUP_TABLE
CALL 	DISPLAY
MOVFW 	BINARY
CALL 	GETTENS
CALL 	LOOKUP_TABLE
CALL 	DISPLAY
MOVFW 	BINARY
CALL 	GETONES
CALL 	LOOKUP_TABLE
CALL 	DISPLAY
RETURN

; ------------------------------------------- 
; RECEIVES BYTES 
; ------------------------------------------- 
; This routine does not return until a character is received. 
; 
RECEIVE:		 	
btfss 	PIR1,RCIF         ; (5) check for received data 
goto 	RECEIVE 
movf RCREG,W          ; save received data in W 
BTFSC	STATUS,Z
GOTO	RECEIVE
BCF  RCSTA,CREN
BSF  RCSTA,CREN		 

return 

; ------------------------------------------------------------- 
; SENDS BYTES 
; ------------------------------------------------------------- 
; 
SEND:    
movwf TXREG            ; send data in W 
BCF PIR1,RCIF
BSF     STATUS,RP0
WtHere 
btfss TXSTA,TRMT        ; (1) transmission is complete if hi 
goto WtHere 
BCF     STATUS,RP0
return 	
;--------------------------------------------------------------
;INITIALISES UART
;--------------------------------------------------------------
	
UART_SETUP:				;This should give a Baud Rate of just over 1500.  
;BSF		OSCCON,SCS
bsf		STATUS,RP0
movlw 	D'207'            ;207 GIVES 300BPS NO ERROR AT THIS BAUD RATE 
movwf 	SPBRG 
movlw 	b'00100000'       ; brgh = low (2) 
movwf 	TXSTA             ; enable Async Transmission, set brgh 
bcf 	STATUS,RP0          ; RAM PAGE 0 
movlw 	b'10010000'       ; enable Async Reception 
movwf 	RCSTA 
return 
;-------------------------------------------------------------
;INTIALISES UART FOR BAUD RATE OF 4800? 
;-------------------------------------------------------------

GPSUART_SETUP:
BCF		OSCCON,SCS
bsf		STATUS,RP0
movlw 	D'191'              ; 0x19=9600 bps (0x0C=19200 bps) 
movwf 	SPBRG 
movlw 	b'00100100'       ; brgh = high (2) 
movwf 	TXSTA             ; enable Async Transmission, set brgh 
bcf 	STATUS,RP0          ; RAM PAGE 0 
movlw 	b'10010000'       ; enable Async Reception 
movwf 	RCSTA 
return 


;------------------------------------------------------------
; INTILAISES LCD 
;------------------------------------------------------------
INIT_LCD:
CALL  	MILLISEC30
MOVLW 	B'00111000'    ;tell display its two line0
CALL	COMMAND
MOVLW 	B'00001110'
CALL	COMMAND
CALL	CLEARSCREEN
MOVLW 	B'00000110'
CALL	COMMAND 

RETURN

;------------------------------------------------------------
; MOVES DDRAM TO BEGININNING OF SECOND LINE
;------------------------------------------------------------
SECOND_LINE:
MOVLW LIN2                     ;set to line 2
CALL COMMAND                   ;output to the screen
RETURN
;------------------------------------------------------------
; EXECUTES COMMANDS IN W FOR LCD 
;-----------------------------------------------------------
COMMAND:
BCF RS  
BCF	RW                         ;command coming
MOVWF LCD                      ;PUT OUT ONTO PORT
BSF E                          ;make sure the enable line is up 
CALL MICROSEC50                 ;WAIT
BCF E                          ;clock the data in
BSF	RS
RETURN
;************************************************************
; DISPLAYS CONTENTS OF W ON LCD
;************************************************************
DISPLAY:                   ;make sure it will accept data
BSF RS     
BCF	RW  
MOVWF	LCD                ;send data to lcd
BSF	E                        ;make sure the enable line is up 
CALL MICROSEC50
BCF E 
CALL MICROSEC50                         ;clock the data in  
BSF	 RS               
RETURN
;------------------------------------------------------------
;CLEARS SCREEN OF LCD
;------------------------------------------------------------
CLEARSCREEN:
BCF 	RS 
BCF		RW
MOVLW	D'1'
MOVWF	LCD 
BSF		E
CALL	MILLISEC2 	
BCF		E
CALL	MILLISEC2
RETURN
;---------------------------------------------
;RETURNS NUMBER OF HUNDERS FOR VALUE IN W
;---------------------------------------------
GETHNDS	
		movwf	t1
        clrf    w2
gethnds_loop
		movlw	.100
		incf	w2,f
		subwf	t1,f
		btfsc	STATUS,C
		goto 	gethnds_loop
		decf	w2,w
		return		
;--------------------------------------------
;RETURNS NUMBER OF TENS FOR VALUE IN W
;--------------------------------------------
GETTENS	
		movwf	t1
        clrf    w2
gettens_loop	movlw	.10
		incf	w2,f
		subwf	t1,f
		btfsc	STATUS,C
		goto 	gettens_loop
		decf	w2,w
		goto	GETONES

;----------------------------------------------
;RETURNS NUMBER OF ONES FOR VALUE STORED IN W
;-------------------------------------------------
GETONES		movwf	w2
		movlw	.10
deltens_loop	subwf	w2,f
		btfsc	STATUS,C
		goto 	deltens_loop
		addwf	w2,w
		return

;--------------------------------------------------------------------------------------
;COMPARES 16-BIT NUMBER 
;SETS BIT 0 OF SAMPLEREG IF NEW SAMPLE WAS GREATER THAN THE OLD 
;--------------------------------------------------------------------------------------

LARGECOMPAREOLDGTNEW: 


MOVFW SAMPLEOLDLOW		;MOVES LOW BYTE OF OLD SAMPLE TO W
SUBWF SAMPLENEWLOW,w	;SUBTRACTS LOW BYTE OF OLD SAMPLE FROM NEW SAMPLE 
MOVFW SAMPLEOLDHIGH		;MOVES HIGH BYTE OF OLD SAMPLE TO W
SKPC 					;IF THE CARRY FLAG IS SET SAMPLENEW-SAMPLEOLD WAS POS OR 0 AND NEXT INSTRUCTION WILL BE SKIPPED
INCFSZ SAMPLEOLDHIGH,w 	;INCREMENTS OLD SAMPLE. IF IT ZERO  GOES TO NEXT INSTRUCTION.
SUBWF SAMPLENEWHIGH,w	;SUBTRACTS HIGH BYTE OF OLD SAMPLE FROM NEW.
SKPNC					;IF OLD WAS GREATER THAN NEW BIT ZERO OF SAMPLEREG IS CLEARED  
BCF	  SAMPLEREG,0		
SKPC  					;IF NEW WAS GREATER THAN OLD BIT 0 OF SAMPLEREG IS SET
BSF	  SAMPLEREG,0
RETURN 

;-------------------------------------------------------- 
;DISPLAYS THE LETTER Y
;--------------------------------------------------------
LETTER:
CLRF	TIMERCOUNTER
MOVLW	'Y'
CALL 	DISPLAY
RETURN
;--------------------------------------------------------
;ENABLES INTERRUPTS FROM TIMER 1
;--------------------------------------------------------
INTERRUPTSETUP: 
bsf 	STATUS,RP0		;SWITCH TO BANK ONE 
bsf 	PIE1,TMR1IF 	;ENABLE TIMER1 INTERRUPT 
bcf		STATUS,RP0		;SWITCH TO BANK ZERO
bsf 	INTCON,7 		;ENABLE GLOBAL INTERRUPTS 
BSF		INTCON,PEIE 	;ENABLE PERIPHERAL INTERRUPTS 
CLRF 	TMR1L			;CLEAR TIMER COUNTER
CLRF	TMR1H
MOVLW	B'00110000'		;BITS 5-4 GIVES 1:8 PRESCALER. BIT 1=0 USE INTERNAL CLOCK/4.
MOVWF	T1CON			
BSF		T1CON,0 		;ENABLES TIMER
RETURN



;----------------------------------------------
;30 MILLI-SECOND DELAY FOR 14.7456 MHz CLOCK
;----------------------------------------------
MILLISEC30:
movlw	0x65
movwf	D1
movlw	0x57
movwf	D2
Delay_1
decfsz	D1, f
goto	$+2
decfsz	D2, f
goto	Delay_1

			;4 cycles
goto	$+1
goto	$+1
RETURN
;-----------------------------------------------
;2 MILLISECOND DELAY FOR 14.7456 MHz CLOCK 
;-----------------------------------------------
MILLISEC2
movlw	0xC2
movwf	D3
movlw	0x06
movwf	D2
Delay_2
decfsz	D3, f
goto	$+2
decfsz	D2, f
goto	Delay_2
;------------------------------------------------
;50 MICROSECOND DELAY FOR 14.7456 MHz CLOCK
;------------------------------------------------
MICROSEC50:
			;184 cycles
movlw	0x3D
movwf	D4
Delay_3
decfsz	D4, f
goto	Delay_3

RETURN
;--------------------------------------------------
;TEN SECOND DELAY FOR 14.7456 CLOCK
;---------------------------------------------------
TENSECONDS:
movlw	0x01
movwf	D5
movlw	0x5C
movwf	D6
movlw	0x51
movwf	D7
Delay_0
decfsz	D5, f
goto	$+2
decfsz	D6, f
goto	$+2
decfsz	D7, f
goto	Delay_0

RETURN
;-------------------------------------------------------
;4 MHZ-1SECOND
;-------------------------------------------------------
SECOND:
movlw	0x08
	movwf	D8
	movlw	0x2F
	movwf	D9
	movlw	0x03
	movwf	D10
Delay_6
	decfsz	D8, f
	goto	$+2
	decfsz	D9, f
	goto	$+2
	decfsz	D10, f
	goto	Delay_6

			;3 cycles
	goto	$+1
	nop
RETURN

     
END

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