ADC and Interrupt on Change
I currently have a project which checks for changes on a trim pot as part of the main loop (the trim pot/ADC value then controls the brightness of a LED). It samples 16 readings and then sorts them and takes the average of the middle 8. This works well for getting a pretty stable ADC value but I'm wondering if I can move this to an interrupt-on-change interrupt routine to free up the main loop to do other stuff (that might include PAUSE). Does it make sense to use Darrel's DT_INTS-14.bas & IOC_INT with ADC or would it just be firing way too often?
Re: ADC and Interrupt on Change
Quote:
Does it make sense to use Darrel's DT_INTS-14.bas & IOC_INT with ADC or would it just be firing way too often?
no IOC is change of logic level ie 0 to 1 or 1 to 0 not change in adc value
if your adc readings fluctuate that much are your adc settings appropriate ?
why not quantise your adc readings to a finite range of pwm values
see these examples about int driven adc measurements
http://www.picbasic.co.uk/forum/showthread.php?t=21072
Re: ADC and Interrupt on Change
Quote:
Originally Posted by
richard
no IOC is change of logic level ie 0 to 1 or 1 to 0 not change in adc value
if your adc readings fluctuate that much are your adc settings appropriate ?
why not quantise your adc readings to a finite range of pwm values
see these examples about int driven adc measurements
http://www.picbasic.co.uk/forum/showthread.php?t=21072
Thanks richard - that's what I suspected. The reason I wanted to move the ADC check to an IOC_INT was I had code in the Main loop to pulsate a LED which had PAUSEs in it which meant that you could change the trim pot but it would be a while before it read it (and hence appear jerky). So, instead I'm now using DT's ELAPSED_INT.bas and checking the 'Seconds' variable to decide if I want to pulsate the LED. This seems to work much better with pretty good response time in terms of reading the changed trim pot value.
BTW, I am scaling the ads readings to a range of PWM steps and then using a 'gamma correction' table to set the actual PWM value:
Code:
' For production version of this code, comment out the line below re:
' LCD debugging and also update config fuses to have code protect on
'#DEFINE USE_LCD_FOR_DEBUG ; comment out for non-debug use
' ***************************************************************
' Pin Connections
' ***************************************************************
' VDD -> pin 1 -> +5V
' RA5/Rc -> pin 2 -> EUSART receive
' RA2 -> pin 5 -> 1kohm -> 2N2222A transistor -> LEDs
' RA1 -> pin 6 -> Trim pot input
' RA0/Tx -> pin 7 -> EUSART transmit (LCD)
' VSS -> pin 8 -> GND
DEFINE OSC 16 ; Set oscillator 16Mhz
' ***************************************************************
' EUSART Settings for Tx/Rc (e.g. LCD)
' ***************************************************************
' > use Mister E PIC Multi-Calc application to get register/DEFINE settings
' > as the values are dependent on the OSC and desired baud rate
DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
DEFINE HSER_CLROERR 1 ' Clear overflow automatically
DEFINE HSER_SPBRG 160 ' 9600 Baud @ 16MHz, -0.08%
' ***************************************************************
' Device Fuses
' ***************************************************************
' PIC chip data sheets can be found here: C:\Program Files\Microchip\MPASM Suite
#CONFIG
__config _CONFIG1, _FOSC_INTOSC & _WDTE_ON & _PWRTE_ON & _MCLRE_OFF & _CP_OFF & _CPD_OFF
__config _CONFIG2, _PLLEN_OFF & _STVREN_ON & _BORV_LO & _LVP_OFF
#ENDCONFIG
' ***************************************************************
' Initialization
' ***************************************************************
OSCCON = %01111000 ' 16MHz internal osc
pause 100
APFCON.2 = 0 ; Tx on RA0 for LCD display
APFCON.7 = 1 ; Rc on RA5
APFCON.0 = 0 ; CCP1 on RA2
' Some LCD serial modules need inverted data, some do not
' Enable the line below if needed, but for SparkFun SerLCD it should be
' commented out
'BAUDCON.4 = 1 ; Transmit inverted data to the Tx pin
' From Mister E's Multi-Calc (EUSART):
' *****************************************************************
SPBRGH = 1
BAUDCON.3 = 1 ' Enable 16 bit baudrate generator
' *****************************************************************
TRISA = %00100010 ' Make all pins output except for RA1 (trim pot input)
' and RA5 (EUSART Rc)
ANSELA = %00000010 ; Analog on PORTA.1 (AN1) only
FVRCON = 0 ' Fixed Voltage Reference is disabled
ADCON0 = %00000101 ' ADC (analog-to-digital) is enabled on AN1 (RA1) only
PAUSEUS 20 ; wait for the analog switch 'glitch' to die down
ADCON1 = %00110000 ; Left-justified results in 8-bits; Frc as timer
#IFDEF USE_LCD_FOR_DEBUG
LCD_INST CON 254 ' instruction
LCD_CLR CON 1 ' Clear screen
LCD_L1 CON 128 ' LCD line 1
LCD_L2 CON 192 ' LCD line 2
LCD_SP_CMD CON 124 ' special command character (for adjusting backlight brightness or toggling splash screen)
LCD_BR_LVL CON 140 ' 140==40%
LCD_SPLASH CON 9 ' toggles splash screen display
#ENDIF
' ***************************************************************
' Includes
' ***************************************************************
INCLUDE "DT_INTS-14.bas" ' Base Interrupt System
INCLUDE "ReEnterPBP.bas" ' Include if using PBP interrupts
INCLUDE "Elapsed_INT.bas" ' Contains subs for doing elapsed time
' --> copy files to PBP main folder
' (i.e. c:\pbp3)
ASM
INT_LIST macro ; IntSource, Label, Type, ResetFlag?
INT_Handler TMR1_INT, _ClockCount, PBP, yes
endm
INT_CREATE ; Creates the interrupt processor
INT_ENABLE TMR1_INT ; Enable Timer 1 Interrupts
ENDASM
' LED Fade Linearization
' ======================
' Increasing the duty cycle by discrete integer amounts leads to a logarithmic
' increase in brightness; the LED appears to quickly reach maximum brightness
' long before it reaches the max duty cycle value. To make the fade in look more
' linear (like an incandescent bulb), the data table below uses 'gamma correction'
' to genterate appropriate duty cycle values.
' Array size = 100
' Total PWM steps: 512
' Gamma correction: 0.75 (try values in the range of 0.5 - 2.0)
' # of values per line: 15
'-----[The data table]--------------------------------------------------------
DataWord VAR WORD
numSteps CON 100
DataTable CON EXT
GOTO OverData ; Make sure data doesn't try to execute
ASM
DataTable
DW 0, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4
DW 5, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 11, 12, 12
DW 13, 14, 15, 16, 17, 18, 19, 20, 22, 23, 24, 26, 27, 29, 31
DW 32, 34, 36, 38, 41, 43, 45, 48, 51, 54, 57, 60, 63, 66, 70
DW 74, 78, 82, 87, 91, 96,101,107,112,118,124,131,138,145,152
DW 160,168,177,186,196,205,216,227,238,250,263,276,289,304,319
DW 334,351,368,386,404,424,445,466,488,511
endasm
OverData:
'-----[Continue with code]----------------------------------------------------
' ***************************************************************
' Set up PWM on CCP1
' ***************************************************************
CCP1CON = %00001100 ; Use CCP1 in PWM mode
' Set duty cycle registers initially to 0
CCP1CON.4 = 0
CCP1CON.5 = 0
CCPR1L = 0
' Use Mister E's PICMultiCalc_1.3.1.exe application (Windows only)
' to determine prescaler and PR2 values for given OSC frequency (e.g. 16Mhz)
' and duty cycle (use 100% to see highest actual value)
' ************************
' CCP1 uses TMR2
' ************************
T2CON = %00000110 ; Timer2 on with 1:16 prescaler
PR2 = 127 ; For 16Mhz OSC the desired output freq of 1954Hz
; is achieved with this PR2 value (9-bit resolution
; with 1:16 prescaler)
; MAX DUTY = 512; must match max PWM steps from data
; table above
PWMDuty VAR WORD ; Duty cycle variable for PWM
MaxADCVal CON 255 ; 255 for 8-bit; 1023 for 10-bit
ADCInVal VAR BYTE ; stores ADCIN result read from trim pot
compVal VAR BYTE ; stores last-changed ADC value
CounterA var BYTE ' Just a BYTE Temporary working variable
DataW var WORD ' Just a WORD Temporary working variable
RawData var BYTE [16] ' Array holding ADC Result
LEDBrIndx VAR WORD
i VAR WORD
PulseLimit VAR WORD
LEDPulse VAR BIT ; 1=fully on; 0= start pulsating effect
LCDPause CON 5 ; Pause for LCD display
FadeInPause VAR BYTE ; Pause during LED fade in
#IFDEF USE_LCD_FOR_DEBUG
FadeInPause = 12
#ELSE
FadeInPause = 40 + LCDPause ; was 15 + LCDPause
#ENDIF
#IFDEF USE_LCD_FOR_DEBUG
pause 1000
HSEROUT [LCD_INST, LCD_CLR, "LCD Init"]
pause LCDPause
HSEROUT [LCD_INST, LCD_L2, " SerLCD_V2_5"]
pause 2000
#ENDIF
' ************************************************
' Get Vref from ADC to set brightness step index
' ************************************************
GOSUB Do_ADC
compVal = ADCInVal ; set initial compare value
GOSUB Map_ADCInVal_to_PWM_Steps
#IFDEF USE_LCD_FOR_DEBUG
HSEROUT [LCD_INST, LCD_CLR]
pause LCDPause
HSEROUT ["LEDBrIndx=",DEC LEDBrIndx," "]
pause 750
#ELSE
PAUSE 500 ; should match motor spin up
#ENDIF
' Fade in LED to set brightness
FOR i = 0 to (LEDBrIndx - 1) ; max is 'numSteps' from data table above
ReadCODE (DataTable + i), DataWord
PWMDuty = DataWord
GOSUB ChngLEDBrightness
#IFDEF USE_LCD_FOR_DEBUG
HSEROUT [LCD_INST, LCD_CLR]
pause LCDPause
HSEROUT ["PWMDuty=",DEC PWMDuty," "]
#ENDIF
pause FadeInPause ; should match motor spin up
NEXT i
LEDPulse = 1 ' set initial value
Gosub ResetTime ' Reset Time to 0d-00:00:00.00
Gosub StartTimer ' Start the Elapsed Timer
Main:
' Check trim pot value
GOSUB Do_ADC
' PAUSE 100
' If trim pot value has changed, update LED brightness level
If (compVal > (ADCInVal + 1)) or (compVal < (ADCInVal - 1)) THEn
compVal = ADCInVal
GOSUB Map_ADCInVal_to_PWM_Steps
ReadCODE (DataTable + (LEDBrIndx - 1)), DataWord
PWMDuty = DataWord
gosub ChngLEDBrightness
#IFDEF USE_LCD_FOR_DEBUG
HSEROUT [LCD_INST, LCD_CLR]
pause LCDPause
HSEROUT ["new LEDBrIndx", LCD_INST, LCD_L2, DEC LEDBrIndx, " "]
#ENDIF
Gosub ResetTime ' Reset Time to 0d-00:00:00.00
ENDIF
' PulseLimit = 3*(LEDBrIndx/4) ' 75%
PulseLimit = LEDBrIndx/2 ' 50%
' PulseLimit = LEDBrIndx/4 ' 25%
' Pulse LEDs
if (Seconds = 2) AND (LEDPulse = 1) then
' Fade down LEDs to a preset minimum
FOR i = (LEDBrIndx - 1) to PulseLimit STEP -1
ReadCODE (DataTable + i), DataWord
PWMDuty = DataWord
GOSUB ChngLEDBrightness
#IFDEF USE_LCD_FOR_DEBUG
HSEROUT [LCD_INST, LCD_CLR]
pause LCDPause
HSEROUT ["PWMDuty=",DEC PWMDuty," "]
#ENDIF
pause 25
NEXT i
LEDPulse = 0
Gosub ResetTime ' Reset Time to 0d-00:00:00.00
'LCDout $FE,$C0, dec Days,"d-",dec2 Hours,":",dec2 Minutes,":",dec2 Seconds
ELSEIF (Ticks = 25) and (LEDPulse = 0) THEN
' Fade up LEDs back to trim pot setting
FOR i = PulseLimit to (LEDBrIndx - 1)
ReadCODE (DataTable + i), DataWord
PWMDuty = DataWord
GOSUB ChngLEDBrightness
#IFDEF USE_LCD_FOR_DEBUG
HSEROUT [LCD_INST, LCD_CLR]
pause LCDPause
HSEROUT ["PWMDuty=",DEC PWMDuty," "]
#ENDIF
pause 25
NEXT i
LEDPulse = 1
Gosub ResetTime ' Reset Time to 0d-00:00:00.00
'LCDout $FE,$C0, dec Days,"d-",dec2 Hours,":",dec2 Minutes,":",dec2 Seconds
endif
GOTO Main
Do_ADC:
' Function to 'average out' changing ADC values when the trim pot swiper arm
' isn't moving to get a steady value
' Stuff 16 Element WORD Array full of ADC values
' ----------------------------------------------
For CounterA = 0 to (16 - 1)
ADCON0 = %00000101 ' Select Channel, Turn-On A/D
' 7=0 Unused
' 6=0 Unused
' 5=0 )
' 4=0 )
' 3=0 ) selects AN1
' 2=0 )
' 1=0 Go-done Bit
' 0=1 switch-On ADC Module
Pauseus 50 ' Wait for channel to setup
ADCON0.1 = 1 ' Start conversion
While ADCON0.1=1:Wend ' Wait for conversion
' DataW.HighByte=ADRESH
' DataW.LowByte=ADRESL
DataW = ADRESH ' Read variable from ADC and save
RawData(CounterA) = DataW
Next CounterA
' Sort ADC Input
' --------------
CounterA = 0
GetADCSortLoop:
If RawData(CounterA + 1) < RawData(CounterA) then
DataW = RawData(CounterA)
RawData(CounterA) = RawData(CounterA+1)
RawData(CounterA+1) = DataW
If CounterA > 0 then CounterA = CounterA - 2
endif
CounterA=CounterA+1
If CounterA < (16 - 1) then goto GetADCSortLoop
' Quanticise, discarding top and bottom FOUR elements
' ----------------------------------------------------
DataW = 0
For CounterA = 4 to 11
DataW = DataW+RawData(CounterA)
Next CounterA
ADCInVal = DataW>>3 ' Divide Result by EIGHT
return
'*********** Map Vref to PWM step **************************************
Map_ADCInVal_to_PWM_Steps:
' Map ADC value to the range of accetable PWM steps, as the two ranges may
' not be the same( e.g. ADC: 0-255, PWM: 50-100)
' Arduino Map function to emulate:
' ===============================
' map(value, fromLow, fromHigh, toLow, toHigh)
' long map(long x, long in_min, long in_max, long out_min, long out_max)
' {
' return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
' }
' Need to split up the operations to get full value using DIV32
' 50% PWM step range
'LEDBrIndx = ((compVal - 0) * (numSteps - numSteps/2))
'LEDBrIndx = DIV32 (MaxADCVal - 0) + numSteps/2
' 90% PWM step range
LEDBrIndx = ((compVal - 0) * (numSteps - numSteps/10))
LEDBrIndx = DIV32 (MaxADCVal - 0) + numSteps/10
RETURN
'*********** Set duty registers ****************************************
ChngLEDBrightness:
CCP1CON.4 = PWMDuty.0
CCP1CON.5 = PWMDuty.1
CCPR1L = PWMDuty >> 2
RETURN
