Capacitive sensing with the CSM module, 16F1823 & learning about interrupts

[Max Power]

so, this is a continuation of the thread started by ero, named 'Capacitive Touch Button by using ADC channel (the CVD system)' that I sort of hijacked. HankMcSpank helped me out a ton. Many thanks to him. He left enough clues in his code snippits to point me in the right direction, but if you blindly copy and paste his code, you'll be using timer0 for both cap sense counting, and timing, which is not going to work. Once I figured that out, that was my 'Ah-Ha' moment!

I've been avoiding interrupts like the plague, so this will, I'm sure, help me (and maybe somebody else)learn something about them. I'll be thinking out loud some of my questions, like, how often is this interrupt firing, and how fast is the cap sensor oscillating? but for now, I'm going to bed! (with a big smile on my face, cuz this thing is working now!)

I get about 19000 with nothing near the sensor, and about 7500 with my fingers covering as much of the sensor as possible, and about 6000 if I actually touch the copper tape.

I couldn't program the chip with my PICKIT2, I needed the PICKIT3. So I program with the PICKIT3 and then connect the PICKIT2 to use the UART tool. Doesn't the PICKIT3 have a uart monitor?

I'm guessing I don't have to clear the timer0 registers at the end of the interrupt routine...

here is the code


'MPLAB 8.70, PICBASIC PRO Compiler 2.60C, Darrel Taylor Instant Interrupts-14_V110 (http://darreltaylor.com/DT_INTS-14/intro.html)
'PIC16F1823 14 PIN dip package


@ __CONFIG _CONFIG1, _FCMEN_OFF & _FOSC_INTOSC & _WDTE_SWDTEN & _MCLRE_OFF & _CP_OFF & _IESO_OFF & _BOREN_OFF & _PWRTE_OFF
@ __CONFIG _CONFIG2, _LVP_OFF

DEFINE OSC 8 'tell picbasic what speed the oscillator is

DEFINE DEBUG_REG PORTA ' asyncronous bit-banged RS-232 output on PORTA...
DEFINE DEBUG_BIT 0 ' bit 0, which can be seen with the PICKIT2 UART tool, but you can't program this chip with the PICKIT2?!?!
DEFINE DEBUG_BAUD 9600 ' 9600 Baud,
DEFINE DEBUG_MODE 0 ' 1 = inverted, 0 = true,like for using max232, or pickit2
DEFINE DEBUG_PACING 1000 ' 1mS delay

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

OSCCON = %01110010
'0 = 4x PLL is disabled
'1110 = 8 MHz
'0 = unused
'1X = Internal oscillator


ANSELA = %00000000 'make port A pins digital
TRISA = %00000000 'make port A pins outputs

ANSELC = %00000010 'make pin 9 (RC1) (CPS5) analog
TRISC = %00000010 'make pin 9 (RC1) (CPS5) input


OPTION_REG = %10000111
'1 = All weak pull-ups are disabled (except MCLR, if it is enabled)
'0 = Interrupt on falling edge of RB0/INT pin
'(TMR0CS) 0 = Transition on RA4/T0CKI pin
'0 = Increment on low-to-high transition on RA4/T0CKI pin
'0 = Prescaler is assigned to the Timer0 module
'111 = 1:256 Timer0 prescaler rate

T1CON = %11000001 'enable timer 1 (bit 0) & source the clock from the CPS module (bit 6 & 7 =11

CPSCON0 = %10001100 'set the CPS module highest frequency availabe (for vcc mode) + timer0 clock sourced from CPS module. (BIT 1)
'1 = CPS module is enabled
'0 = CPS module is in the low range. Internal oscillator voltage references are used.
'00 = unused
'11 = Oscillator is in High Range. Charge/Discharge Current is nominally 18 μA
'0 = Capacitive Sensing Oscillator Status bit (only readable)
'0 = Timer0 clock source is controlled by the core/Timer0 module and is FOSC/4

CPSCON1 = %00000101 '0101 = channel 5, (CPS5)

CM1CON0 = 0 ' COMPARATOR OFF
CM1CON1 = 0 ' COMPARATOR OFF

DEBUG "Starting Up",13,10

CPS5_PRESENTCOUNT var WORD
CPS5_THRESHOLD var WORD
CPS5_LASTCOUNT var WORD

ASM
INT_LIST macro ; IntSource, Label, Type, ResetFlag?
INT_Handler TMR0_INT, _Timer0_Int, pbp, yes
endm
INT_CREATE ; Creates the interrupt processor
ENDASM

TMR0 = 0 'clear TIMER0
@ INT_ENABLE TMR0_INT 'enable timer0 interrupts

main:
pause 100
@ INT_DISABLE TMR0_INT ' stop timer0 interrupts
DEBUG DEC CPS5_PRESENTCOUNT,13,10
@ INT_ENABLE TMR0_INT ' re-enable timer0 interrupt

goto main

'************************************************* *************************************************
Timer0_Int:
@ INT_DISABLE TMR0_INT ' stop timer0 interrupts while we're in here
CPS5_PRESENTCOUNT = TMR1 ' take a snapshot of Timer1's present count.

'CPS5_THRESHOLD = CPS5_LASTCOUNT - ((CPS5_LASTCOUNT/100)*2) ' this sets the 'trigger' up for a 20% diversion (finger press)
''CPS5_LASTCOUNT = CPS5_PRESENTCOUNT ' store away the present timer0count for the next time we come into the interrupt routine
'if CPS5_PRESENTCOUNT < CPS5_THRESHOLD then 'if the present incoming timer0 count is 20% below the last count, then a finger has been placed on the sensor

TMR0 = 0 ' clear TIMER0
TMR1 = 0 ' clear TIMER1
@ INT_ENABLE TMR0_INT ' re-enable timer0 interrupt
@ INT_RETURN
end

[HankMcSpank]

Firstly big oops on my part... :o no, you can't use timer0 for both the interrupt AND the CPS oscillator output counting, (like I say, my snippets were from a humungous program that I hacked very quickly & tried to condense as much as possible - got carried away clearly) but hey you got there!!

Any way as you've done, it's best to use timer1 for counting the CPS pulses, and timer0 for the timebase.

You can program the 16f1823 with a Pickit2 (http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en027813) ....just make sure you've the latest PIckit2 device file

Yes, it's best to clear timer0 at the end of the timer0 interupt (though this'll be the point we're the old hands chime in "no need, it gets cleared for you", etc)

The thing about CPS that doesn't get mentioned, is using DT's interrupts coupled with the high interrupt rate normally needed for a decent sensor feel/response, means your little pic is working quite hard just for cap touch alone ...therefore, you want to interrupt as little as you can get away with but still have a decent sensor response feel. For example, if you only interrupt every half second, it might feel sluggish (also the longer you make the period between interrupts, the more you timer1 is gonna count oscillator pulses - watch the timer1 oscillator count doesn't get near 65536 and overflow, if it's getting towards that, take the CPS oscillator frequency down with the CPSCON register setting (bits 4-2)

[HankMcSpank]

I'm wondering if we can tempt one of the experienced assembly guys here, to leverage on the "Automatic Context saving" interrupt capability aspect of these new line of PICs, which would place much less burden on the PIC when cap touch is used for switching.

All we need the associated assembly interrupt to do is this...

1. store the present timer1 count
2. setup a running count 'threshold' (by deducting x% from the last timer1 count)
3. compare present timer1 count with the 'threshold' .....if it is below, then a sensor has been touched, set a 'sensor touched' type flag, if the present timer1 count is not below the threshold, then store 'present timer1 count' away as 'last timer1 count' (for the next interrupt)

job done!

Else, if you have a lot of time sensitive stuff going on in your main loop, I fear you almost need to dedicate one pic (eg a 12f1822) solely to cap touch switching duties, due to the high frequency of interrupts needed & the chunky overhead they presently incur.

[Max Power]

OK. I'm missing something here. How do I make sure I have the latest PICKIT2 device file? will I be able to program the 16F1823 in MPLab, or just the stand alone program?

on Microchip's PICkit 2 Development Programmer/Debugger page, I see the stand alone program v2.61, then the device file, which gives me the PK2DeviceFile-1.62.09.dat file. I deleted the -1.62.09 from the name and replaced the old file with the new one in the program files\Microchip\PICkit 2v2 directory.

Then when I run the stand alone PICkit2 v2.61 program, I still don't see the 16F1823 in the drop down menu. and MPLAB still has the PICKIT2 greyed out when I load my workspace.

THen, back to the Microchip PICkit 2 Development Programmer/Debugger page I see the PK2CMDv1.20 - do I need to put that somewhere?

[HankMcSpank]

It sounds like you've done everything right, but the only thing I do different is not try & select it in the Pickit standalone app device drop down list (cos it's not listed there!). When you connect your pickit2 to your PIC, then start the pickit2 standalone application, it should detect it.

If not, try....

In the pickit2 app, select 'device family' - 'midrange' - '1.8V min

then 'tools' - 'check communication ...and it should then find it (ie you should see your PIC listed next to the device field)

re MPLab....still finding my feet with that interface, I don't go there much for now, but here the pickit2 is greyed out too....go figure, the pickit2 standalone app works, but microchips IDE doesn't!

re the Pickit3...in my opinion it blows (for a start, there's no UART tool)

[igeorge]

I try to use the CVD method on a pic18f but i did not have any luck
The 18f does not have CSM , they have only mtouch
The issue with mtouch is that you must touch the sensor to get a response, and if you put a piece of plastic 2-3 mm no way to get it working
Does anybody has a pieces of working code for pic18f so i can experiment wit capacitive voltage divider method ?
Thank you