12F683 interrupt on change improvement?

[achilles03]

I have a project using three 12F683s controlled by a 16F883 master. The goal of the project is to track the RPM of 4 independant propellers on a quadcopter using an IR photodiode and emitter (i.e. a beam breaker). When the propeller blade crosses between the IR photodiode and emitter, the voltage at the interrupt pin drops to ~0.7V (a 3.3k resistor to GND). When the blade moves out of the way, the voltage at the interrupt pin increases to ~4.8V. The IR setups for the 16F883 and the 12F683s are effectively identical (same wire lengths, same IR components, resistors, etc). The 16F883 drives an 8Mhz xtal osc with the osc2 pin tied to the osc1 pins of the 12F683s (short distance). The 16F883 starts the process and takes a pin high that tells the 12F683s to start logging data. The 16F883 also begins logging data. I opted to use 4 PICs as the props can spin around 9000RPM, which is ~300 interrupts per second (2 blades per prop) and I'm not sure how I'd get it to work with interrupts occuring that frequently and occasionally falling on top of each other.

My problem is that the 12F683s are not that reliable and the data is poor, however the 16F883 seems to be logging the blade interrupts great. Below are 2 examples of a 25 second run:




As is apparent, the 883 is doing great, but the 12F683s are not (data from all 12F683s is similar). The IR max and min voltages are meeting the high/low logic requirements (0.7V low, 4.8V high) and the IR setups are effectively the same for all 4 PICs, so I'm wondering if there's some register or code modification I can do to improve the 12F683 interrupts? Or is this more of a hardware issue between the 16F883 and 12F683?

Below is the code for the 12F683 PICs. The code and interrupt for the 16F883 is similar (identical interrupt routine in fact). Thanks in advance for any help or suggestions!
Dave

'PIC-12F683
#CONFIG
__config _FOSC_EC & _WDT_OFF & _CP_OFF & _MCLRE_OFF & _PWRTE_ON & _CPD_OFF &_FCMEN_OFF &_IESO_OFF 
#ENDCONFIG 

DEFINE OSC 8

'Initialize Regsters:
TRISIO =%101111 'I or O; MCLR is pin3
CMCON0 = 7 'Analog comparators off
ADCON0 = 0
ANSEL = 0 'all inputs digital, the adcin command automatically converts it to analog
CCP1CON=%00000000 'disable PWM mode
IOC=%00000100
OPTION_REG=%11000000 ' Interrupt on rising edge INTEDG bit, disable internal pullups

'pins and variables
EE_DAT     var GPIO.1
EE_CLK     var GPIO.0                                              
INT_PIN    VAR GPIO.2
MODEPIN    VAR GPIO.3  'MCLR
OUTPIN     VAR GPIO.4  'OUTPIN also hooked up to an LED

wsave       var    byte $20 SYSTEM
wsave1      var    byte $A0 SYSTEM
pausetime1  var    word
pausetime2  var    word
hbfix       var    byte
ibit        var    bit
n           var    byte
wconfig     var    byte
address     var    word
wbit        var    bit

INCLUDE "DT_INTS-14.bas" ' Base Interrupt System
INCLUDE "ReEnterPBP.bas" ' Include if using PBP interrupts

ASM
INT_LIST macro ; IntSource, Label, Type, ResetFlag?
INT_Handler GPC_INT, _PULSE_WIDTH, PBP, yes
endm
INT_CREATE ; Creates the interrupt processor
ENDASM

@ INT_DISABLE GPC_INT ; disable external (INT) interrupts      

wconfig=%10100000

'At 8Mhz with 1:1 prescaler 
T1CON = %00000000 ' Prescaler = 1:1, timer off

low OUTPIN
pause 500

waitforstart:
OUTPIN=INT_PIN  'toggles LED on OUTPIN to make sure IR sensor is reading high (clear) or low (blade in the way)
if MODEPIN=1 then waitforstart

high OUTPIN
wbit=0 'initial write bit setting to make sure eeprom is written every other interrup
TMR1H = 0
TMR1L = 0
ibit=0
address=0
@ bsf     T1CON, TMR1ON   ' Start timer
@ INT_ENABLE GPC_INT ; enable external (INT) interrupts

main:
if MODEPIN=1 then waitforstart
if ibit=0 then main
@ INT_DISABLE GPC_INT ; disable external (INT) interrupts
if pausetime2.lowbyte=0 then pausetime2.highbyte=hbfix
if wbit=1 then                   
I2CWRITE EE_DAT,EE_CLK,wconfig,address,[pausetime1,pausetime2]
endif
pausetime1=pausetime2  
address=address+2 'effectively adding 4 to address between eeprom writes
if address=0 then done  'if 0 at this point, rollover of address has occured and eeprom is full
wbit=~wbit
ibit=0
@ INT_ENABLE GPC_INT ; enable external (INT) interrupts
goto main

done:
input EE_CLK
input EE_DAT
low OUTPIN
pause 10
if MODEPIN=0 then done

goto waitforstart

'---[INT - interrupt handler]---------------------------------------------------
PULSE_WIDTH:     
pausetime2.highbyte = TMR1H
pausetime2.lowbyte  = TMR1L
hbfix = TMR1H
ibit=1
@ INT_RETURN

end

[achilles03]

I had thought - should I be using "INT_INT" instead of "GPC_INT"? It is set up using GPIO.2 as the interrupt pin, which is the dedicated INT pin per the datasheet. Can you set up an interrupt on GPIO.2 as you would any of the other viable GPIOs OR as the dedicated external interrupt? Looking at the INTCON register, seems like you can set bit 3 (GPIE) for any GPIO interrupt or bit 4 (INTE) specific to GP2/INT? Seems to compile OK with "INT_INT"...? I'm trying to understand the differences if they are both viable methods to set it up?

[richard]

should I be using "INT_INT" instead of "GPC_INT"?

i would



you are not using IOC correctly since the gpio is never read in the isr to clear the change condition


4.2.3 INTERRUPT-ON-CHANGE
Each of the GPIO pins is individually configurable as an
interrupt-on-change pin. Control bits IOCx enable or
disable the interrupt function for each pin. Refer to
Register 4-5. The interrupt-on-change is disabled on a
Power-on Reset.
For enabled interrupt-on-change pins, the values are
compared with the old value latched on the last read of
GPIO. The ‘mismatch’ outputs of the last read are OR’d
together to set the GPIO Change Interrupt Flag bit
(GPIF) in the INTCON register (Register 2-3).
This interrupt can wake the device from Sleep. The
user, in the Interrupt Service Routine, clears the
interrupt by:
a) Any read or write of GPIO. This will end the
mismatch condition, then,
b) Clear the flag bit GPIF.
A mismatch condition will continue to set flag bit GPIF.
Reading GPIO will end the mismatch condition and
allow flag bit GPIF to be cleared. The latch holding the
last read value is not affected by a MCLR nor
Brown-out Reset. After these resets, the GPIF flag will
continue to be set if a mismatch is present.

[Aussie Barry]

Hi Dave,

How clean is the output from your photodiode?
I have been working on a similar setup recently using an encoder wheel and photointerrupter.
I had greater success feeding the MCU's input pin via a schmitt-trigger buffer (SN74LVC1G17 or similar).

I hope this helps.

Cheers
Barry

[achilles03]

Yep, that did it! The output is now as smooth as the 16F883's output. The 16F883 used the INT_INT interrupt from the start. The GPC_INT requires the particulars you noted, and additionally it interrupts on rising or falling edges (new to me). I had only use INT_INT before prior to this application, but encountered problems when I tried it on a 12F629 switching to the GPC_INT, which I later switched to the 12F683 but kept the GPC_INT in error.

Thanks for the comment!
Dave

[richard]

There are less complicated ways i think

'PIC-12F683#CONFIG
  __config _FOSC_EC & _WDT_OFF & _CP_OFF & _MCLRE_OFF & _PWRTE_ON & _CPD_OFF &_FCMEN_OFF &_IESO_OFF 
#ENDCONFIG 


DEFINE OSC 8
    DEFINE DEBUG_REG GPIO
    DEFINE DEBUG_BIT 0      
    DEFINE DEBUG_BAUD 9600
    DEFINE DEBUG_MODE 0 


'Initialize Regsters:
TRISIO =% 101110 'I or O; MCLR is pin3
CMCON0 = 7 'Analog comparators off


ANSEL = 0 'all inputs digital, the adcin command automatically converts it to analog




OPTION_REG=% 11000000 ' Interrupt on rising edge INTEDG bit, disable internal pullups


'pins and variables
                                             
INT_PIN    VAR GPIO.2
OUTPIN     VAR GPIO.4  'OUTPIN also hooked up to an LED


wsave       var    byte $20 SYSTEM
wsave1      var    byte $A0 SYSTEM
time1       var    word  
time2       var    word  
bvars       var    byte  
ibit        VAR    bvars.0     ; TIME BEGIN
wbit        VAR    bvars.1     ; TIME DONE


INCLUDE "DT_INTS-14.bas" ' Base Interrupt System
INCLUDE "ReEnterPBP.bas" ' Include if using PBP interrupts


ASM
INT_LIST macro ; IntSource, Label, Type, ResetFlag?
 INT_Handler INT_INT, _PULSE_WIDTH, PBP, yes
 endm
 INT_CREATE ; Creates the interrupt processor
ENDASM


   




GPIO.0  = 1    ;DEBUG




T1CON = $10 ' Prescaler = 2:1, off


low OUTPIN
pause 200
debug "ready",13 
high OUTPIN
INTCON=$80   ; CLEAR INTF
@ bsf     T1CON, TMR1ON   ' Start timer
@ INT_ENABLE INT_INT ; enable external (INT) interrupts


main:
    if wbit then 
        @ INT_DISABLE INT_INT ; disable external (INT) interrupts
        time1 = time2 - time1
        DEBUG #TIME1,13          ;  prints out cycle count
         ;time1 = time2  
        ibit=0
        wbit=0
        OUTPIN = !OUTPIN
        @ INT_ENABLE INT_INT ; enable external (INT) interrupts
    endif
goto main






'---[INT - interrupt handler]---------------------------------------------------
PULSE_WIDTH: 
    if  ibit=1   then  
        time2.highbyte = TMR1H
        time2.lowbyte  = TMR1L
        wbit=1
    else
        time1.highbyte = TMR1H
        time1.lowbyte  = TMR1L
        ibit=1
    endif
@ INT_RETURN
end

[achilles03]

The output is pretty clean in my experience. I use my photodiode in photoconductive mode (reverse bias), which makes it faster and supposedly noisier but I haven't noticed any noise except in some applications (I note below). The response time seems to be plenty fast in the applications I've used it.

If I were to give a couple suggestions for a similar beambreaker using a photodiode, here's what I would suggest:

• Use it in photoconductive mode for speed
• You want a good IR source that's not a constraint on your design, so make sure you're getting a strong output from the IR emitter. I typically use something like 500 ohm resistors for mine, which means I'm pushing about 8mA from 5V (~1.2V fwd voltage for the diode). You can go higher, but 500 ohms seems to work for me. Fun fact: you can make sure they're working (or not burned out) by using your cell phone camera, which is filtered for human vision but some near IR gets through and shows up as a hazy purple aura around the LEDs.
• I'd recommend using a potentiometer to ground on the output of the photodiode unless you've already played around with it and know what resistance you need. Getting the voltage low enough to trigger low when it's not exposed, and then high enough to trigger high when it is exposed can take some tweaking. A resistance range on the order of 2k-10k seems to work for me most of the time.
• Distance between the photodiode and emitter is a big factor. In my applications, they are typically 1" to 6" apart. So take my suggestions with a grain of salt depending on how far your photodiode is from your emitter.
• If you're photodiode is anywhere near a motor, then shield the wires, make them twisted pairs, put a faraday cage around the motor, and/or verbally threaten the motor. A powered motor will create a lot of EMI that the wires from the photodiode can pick up and will generate a LOT of noise and false high/low triggers. I made an inertial dynamometer to test some motors for drones, and data from some of the larger motors were initially unusable. Making the wires as short as possible, twisting them, wrapping the wires in foil, adding distance between the motor and photodiode wires, and changing the orientation of the motor with respect to the wires fixed it for me.

Hope that helps!
Dave