PCB Etching Tank - Temperature Control - PIC 16F887 & LM35

    ;*******************************************************************************************
    ;*                   PCB Etching Tank - Temperature Control     v 0.E                      *
    ;*-----------------------------------------------------------------------------------------*
    ;*               Jugurtha Hadjar - Raouf Moualdi - Iheb Renai                              *
    ;*-----------------------------------------------------------------------------------------*
    ;*          Pr. Youcef Smara                       Dr. Samir Boukhenous                    *
    ;*-----------------------------------------------------------------------------------------*
    ;*          Université des Sciences et de la Technologie Houari Boumédiène                 *
    ;*-----------------------------------------------------------------------------------------*


    ; PIC used: PIC 16F887 40 PIN, Dual in line. 10 bit ADC. Only 8 bits will be used.
    ; Sensor  : LM 35 (as of this version) . 10mv/°C slope.


    ; TODO: Project Due for June, 26th 2012. Give to Pr Smara.
    ; TODO: Figure out OPTION_REG.
    ; TODO: Delete the goto START line if there's nothing between
    ;       that line and the START label.
    ; TODO: Delete the goto Initialize_PIC if there's nothing below it.


    ; UPDATE 0.D --> 0.E    :   Changing from Left justified, to right justified.
    ;                           We'll be using the lower 8 bits (ADRESL).

    ; If the count is 255, then the temperature is 500°C and voltage = 5V.
    ; so 8 bits are enough.


    ; We'll use some subroutines for temperature checks, etc...

    ;***********************************************************************************
    ;*                                   THE SETUP                                     *
    ;***********************************************************************************

        LIST p=16F887, r=dec, f=inhx8m

    #include "p16F887.inc"


        __config _CPD_OFF  & _LFOSC & _MCLRE_ON  & _CP_OFF & _WDT_OFF & _INTOSC


                                                              ;Watchdog Timer  OFF
                                                              ;Power Up Timer  ON

    #define Relay_Pin  PORTB,1
    #define Sensor_Pin PORTA,0


        cblock 0x20      ; General Purpose Registers start here in a PIC16F887.

            Delay_Counter_1, Delay_Counter_2, Temp_Sensor, Voltage_Sensor_ADC


        endc


    ;******************************************************************************************
    ;*                             OPTION_REG Description                                     *
    ;*----------------------------------------------------------------------------------------*
    ;* Bit7:RBPU(active low) PORTB Pull-Up Enable Bit (1, Disabled)                           *
    ;* Bit6:INTEDG, Interrupt Edge Select Bit(0, Interrupt on falling edge B0/INT)            *
    ;* Bit5:T0CS, TMR0 Clock Source Select Bit (0, Internal Instruction Cycle Clock)          *
    ;* Bit4:T0SE, TMR0 Source Edge Select Bit(1, Increment on Hi-to-Lo transition on RA4)     *
    ;* Bit3:PSA,PRESCALER Assignment Bit(0, Prescaler assigned to TMR0 module)                *
    ;* Bit2-0:PRESCALER Select Bits (110, 1:128)                                              *
    ;******************************************************************************************


        org 0x00              ;Reset Vector.


        goto Initialize_PIC


Initialize_PIC

        clrf PORTA
        clrf PORTB  ; This includes the Relay_Pin (PORTB, 1 - Heater) which is
                    ; cleared (turned off) by default for security measures.
        clrf PORTC


        bcf STATUS, RP0

        movlw 0x96
        banksel OPTION_REG
        movwf OPTION_REG      ; Configure OPTION_REG (81h in Bank1).


          goto START        ; Here we go..


START


Initialize_ADC

        banksel ADCON1
        movlw   b'1000000'  ; Right justified. The ADC has a resolution of 10 bits.
                            ; We'll read the higher 8 bits in ADRESL since the temperatures
                            ; we are interested in won't make it to the 9th or 10th bit.
                            ; VDD & VSS for VCFG1 & VCFG0

        movwf   ADCON1
        banksel TRISA
        bsf     TRISA, 0    ; Set RA0 (Pin2) to Input
        banksel ANSEL
        bsf     ANSEL, 0    ; Set RA0 as Analog ..
                            ; Now RA0 is Analog, and is Input.
                            ; RA0 is ready to receive information
                            ; from the sensor.


        banksel ADCON0
        movlw   b'11000001'     ; The ADCON0 Register:
                                ; ADCS1 ADCS0 CHS2 CHS1 CHS0 GO_DONE - ADON

                                ; ADCS1 ADCS0    : 11 Conversion Clock frequency Frc
                                ;                  4 us typical.
                                ; CHS2 CHS1 CHS0 : 000   RA0
                                ; GO_DONE        : 0 . Setting it to 1 starts conversion.
                                ;                  automatically cleared when conversion is done.
                                ; ADON           : 1 . The ADC is enabled.


        movwf   ADCON0


ADC_Get

        movlw   d'100'          ; A value which will be decreased to lose some time.
        movwf   Delay_Counter_2

        call    Delay       ; Acquisition Time : See Datasheet "ADC time requirements".
                            ; Might as well be the best example of Cargo Cult Programming from me.


        bsf     ADCON0, GO  ; Start Analog to Digital Conversion.
        btfsc   ADCON0, GO  ; Check if the conversion is finished.
        goto    $ - 1

        banksel ADRESH
        movf    ADRESH, w             ; Get the ADRESH byte and put it in Voltage_Sensor_ADC
        movwf   Voltage_Sensor_ADC    ; The value is the digitized analog voltage from the sensor.
                                      ; In order to compare it with a temperature, we need to
                                      ; calculate to which temperature in Celsius a certain
                                      ; voltage from the LM35 corresponds. (10mv/°C).

                                      ; Need to figure out an "easy" way to do multiplication.


    ;------------------------------------------------------------------------
    ;                              Check_High_Threshold
    ;------------------------------------------------------------------------

        movlw   d'86'               ; That's our High Threshold.
        call    Check_Temperature   ; Go to the end of the code
                                    ; in "A Little Story About Conversion" to see
                                    ; where did this value come from.
                                    ; In a nutshell, that's the expected
                                    ; result a temperature of 42 °C would give
                                    ; after being converted by a 10 bits , 5 V Vref. ADC.


        btfss   STATUS, C       ; Is the Temperature from the Sensor
                                ; greater than the High threshold (42°C) ?

        call    Temp_Is_High    ; If yes, i.e the temperature is HIGH, then
                                ; it's time to turn off the heater.
                                ; If not, i.e the Temperature from the sensor
                                ; is less than the High threshold and it's more
                                ; than the Low Threshold, then do nothing.


    ;----------------------------------------------------------------------------
    ;                               Check_Low_Threshold
    ;----------------------------------------------------------------------------

        movlw   d'81'             ; That's our Low Threshold

        call    Check_Temperature ; In order to know if the temperature from
                                  ; the sensor is lesser or greater than our
                                  ; threshold, we need to perform a substraction
                                  ; the Carry flag in the STATUS register tells us
                                  ; something about the sign, thus is it greater or lesser?

        btfsc   STATUS, C         ; Is the result of the substraction in Check_Temperature positive?
                                  ; If yes, it means that the temperature from the sensor
        call    Temp_Is_Low       ; is less than our Low Threshold, hence we need to
                                  ; turn the Relay_Pin on. We call the Temp_Is_Low subroutine for that.


Hysteresis

        goto    ADC_Get         ; Here land all cases that need to keep the state of the heater.
                                ; Basically, all cases have been checked (> High Threshold ? < Low Threshold ? Between the two?)
                                ; And the only thing to do now, is to perform another conversion and
                                ; start a new cycle.


    ;      goto START           TODO: Remove that line at the end if it's not necessary.


    ;----------------------------------------------------------------------------------
    ;                                   SUBROUTINES
    ;----------------------------------------------------------------------------------


;----------------------------------------------------------

Check_Temperature

        subwf   Voltage_Sensor_ADC, w

        return
;----------------------------------------------------------


Temp_Is_Low

        btfss   Relay_Pin   ; Is the relay ON ? If it is, then return. (let it that way)
        bsf     Relay_Pin   ; If it's OFF, then turn it ON and return.

        return
;-----------------------------------------------------------


Temp_Is_High

        btfsc   Relay_Pin   ; Is the Relay OFF? If it is, then return. (let it off).
        bcf     Relay_Pin   ; If it's ON, then turn it OFF and return.

        return
;-----------------------------------------------------------


Delay

        decfsz  Delay_Counter_2, f  ; Teenage wasteland. Lose some time.
        goto    Delay               ; Emo stuff...

        return
;-----------------------------------------------------------


;   A Little Story About Conversion


;   Let's talk about the conversion a bit:
;   Let's say we use Vref = 5V of the supply.
;   The output voltage of the LM35 sensor is
;   Voltage_Sensor = Temperature * 10 / 1000 V
;   Voltage_Sensor = Temperature / 100

;   The result of the conversion of Voltage_Sensor
;   is called Voltage_Sensor_ADC.

;   5 volts input correspond to 255 (8 bits to 1)
;   Voltage_Sensor corresponds to Voltage_Sensor_ADC (or Count)

;   Voltage_Sensor_ADC = Voltage_Sensor * 255 / 5
    Voltage_Sensor_ADC = Voltage_Sensor * 51

;   Knowing that Voltage_Sensor = Temperature / 100

;   We get:

;   Voltage_Sensor_ADC = (Temperature / 100) * 51

;   Voltage_Sensor_ADC = Temperature * (51/100)


;   This means that if the Temperature is 100 °C
;   The result of the conversion will be:
;   100 * 51 / 100 = 51.

;   This relation will help translate the "Count" or
;   Voltage_Sensor_ADC to the corresponding temperature.

;   Temperature = Voltage_Sensor_ADC * (100/51)

;   Which means that when we read ADRESL
;   Let's say it has a value or 30.
;   The Temperature which caused this number is
;   Temperature = 30 * (100/51)
;   Which is roughly 58 °C.

;   Now I get the idea that I can calculate the Count for
;   my two thresholds, and instead of having the PIC compute
;   the corresponding temperature for each acquisition..
;   I'll have it compare each ADRESL with the count corresponding
;   to each threshold.

;   Example: Low_Threshold = 40 °C.
;   Voltage_Sensor_ADC_Low  = 40 * 51 / 100 = 20.4 (we'll worry floating point later).
;   Voltage_Sensor_ADC_High = 42 * 51 / 100 = 21.42.

;   So I'll just match ADRESL with 20 and 21.

;   However ... 20 and 21 are kind of too close.
;   We have two values 2 °C apart (that's huge)
;   Yet, the corresponding counts are very close.
;   That's not good
;   I understand why Ericgibbs and Mr RB insisted on using the whole 10 bits.


;   Maybe use the whole 10 bits like he suggested.

;   5V ---------------> 1023
;   Voltage_Sensor --->  Voltage_Sensor_ADC

;   Voltage_Sensor_ADC = Voltage_Sensor * 1023 / 5
;   Voltage_Sensor_ADC = (Temperature / 100) * 1023 : 5

;   Voltage_Sensor_ADC = Temperature * 1023 / 500

;   For a temperature of 40 °C:
;   Voltage_Sensor_ADC_Low  = 40 * 1023 / 500 = 81.84
;   Voltage_Sensor_ADC_High = 42 * 1023 / 500 = 85.932

;   They are more spaced, so it's better.
;   I'll use the whole 10 bits.
;   Then match ADRESL with 86 and 81 for the thresholds.

        end