DT averaging of interrupt driven cap sensor

[Darrel Taylor]

Well, I think the purpose of averaging with the CSM module is a little different than the Running average routine was written for. But maybe with a couple changes ...

But first, a few other changes are in order.

• Use the USART with HSEROUT for serial comms. It is unaffected by interrupts.
• If you do disable Timer0 to do something else, make sure the Timers get reset, because they will still be counting during that period which could give bad values.
• Stop Timer1 before trying to read the value so the lowbyte can't overflow in-between reading the 2-bytes.
• There is no need to disable Timer0 interrupts in the interrupt handler. Hardware interrupts on 16F1's cannot be interrupted since the GIE bit is cleared by hardware.

Now back to the CSM.
The purpose of averaging the readings is to maintain a baseline of the frequency when it's not being touched. The reading will vary over time due to humidity and temperature.

When you "press" a button, your finger adds capacitance which lowers the frequency. So you can use the FASpread to detect that change, but you don't want to keep averaging or it will change the "baseline" reading.

If you set the FASpread much lower than you have it, I'd guess around 2000 (but try different values). Then change the FastAvg section to ...

; ...
Pressed = 0
GoTo AVGok
FastAvg:
IF Value < AVE THEN 
 Pressed = 1
ELSE
 AVE = Value
ENDIF
GoTo AVGok
RealClose:
Pressed = 0
; ...

[HankMcSpank]

If you look at what I think will be you your proper baseline readings (i.e. once you've addressed a couple of those issues mentioned by Darrel)...

14409 
14439 
14437 
14435
14432
14423 
14433
14440 
14432 
14432 
14426
14435 
14434 
14430 
14429 
14431

they're only varying by about 0.00x% per sample period (interrupt)...and when your finger is pressed on the sensor, you should see the value drop by at least 20% (probably 50% or more if your sensor is decent enough), so there's really no need for averaging.

[Max Power]

thank you so much for the insight. that got rid of the erratic readings. I was able to set a threshold, and not update the average during a button press, and also count the amount of time that the button is pressed. I'm pleased.

but I'm having trouble with the HSEROUT command - I feel so silly, I've never used it before. I saw that the tx pin is the same one as I was using before, so I was encouraged, but all I got in the PICKIT2 UART tool was '????????????????????' and jiberish

I put these two defines up top, I tried 20h and 24h, 9600 baud and 19200
DEFINE HSER_TXSTA 24h ' high speed (BRGH = 1)
DEFINE HSER_BAUD 19200 ' 19200 BAUD rate

and then I had these in my code
Hserout ["Hello World", 13, 10]
HSEROUT [DEC VALUE, ", ", DEC AVE, 13,10]

[HankMcSpank]

This is what gets me there on an 16f1828 @115,200 baud (16Mhz Osc)...

Osccon = %01111010   'sets the internal oscillator to 16Mhz
DEFINE  OSC 16
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 34  ' 115200 Baud @ 16MHz, -0.79%
SPBRGH = 0
BAUDCON.3 = 1         ' Enable 16 bit baudrate generator
RCSTA.7 = 1             ' Enable RB7 for TX USART (not sure if this is needed - needs removing one day to see!)
TrisB.7 = 0                ' set pin 10 RB7 to be an output

MrE's picmulticalc utility helps a lot wrt setting defines for your required serial speed...

http://www.picbasic.co.uk/forum/show...5639#post65639

your command usage looks fine - have you tried scoping the hserout pin?

[Max Power]

yes! I got it working. Thanks for pointing me to the pic multi calc program, what a life saver. I used it for figuring out my interrupt timing, but I didn't see that it also did EUSART settings. It didn't start working until I set the appropriate bit in the APFCON register.

[Ioannis]

I am thinking of using the Cap sensor idea on a project to be battery powered in the middle of the sea.

Considering that there are no 50/60Hz power lines, will this work?

Ioannis

[HankMcSpank]

Considering that there are no 50/60Hz power lines, will this work?

I don't know what you mean wrt power lines bit (grounding?), but I see no reason why it wouldn't work - as far as I recall cap touch works with batteries too. (though now having a little bit of doubt in that all my exploits where on breadboard & mains sourced power!)