Newbie - 16F628A and switch latching

[malc-c]

Hi all,

My first post so be gentile with me

My first project using PBP is for my 12 year old son's model railway. I'm using a 16F628A with the internal 4Mhz OSC as timing is not an issue (and the internal OSC is claimed to be very precise anyway). The project is not rocket science, simply to detect a train via the momentarly activation of a reed switch. This pulse then turns on an LED which is latched on until the same reed switch is activated again.

I have two problems:

1) - The latching is not clean, in that sometimes the LED brightens and remains on when it should be off, or when off it is turned on by the reed switch, but fails to latch

2) - I'm using WinPIC pro to program the PIC. I have set the PIC up for internal OSC no clock out in the code, but I have to change the settings from XT to RC noClockout in the Winpic application. Is the an issue with the Winpic application, or the code (which compiles OK)

Anyway, here is my code.

@INTRC_OSC_NOCLKOUT
@WDT_ON
@PWRT_ON
@MCLR_OFF
@BOD_ON
@LVP_OFF
@CPD_OFF
@PROTECT_OFF

CMCON=7
TRISB=%11101111         'set RB6 as output and the rest input

SW var PORTB.0          'switch input pin 6 (RB0)
LED1 var  PORTB.4       'LED1 on pin 10 (RB4)
Swset var bit

low led1                'RB4 set to LOW (LED1 is off)
Swset=0                 'Var swset is set low

Main:
if SW=0 then            'If switch is LOW (Grounded) then
Toggle Swset            'change swset from 0 to 1
pauseus 200             'debounce delay
endif

If Swset=1 then         'if swset is 1
high led1               'then turn on RB4 (and hence the LED)
else
low led1                'else, LED is off
endif

Goto Main               'go back and keep checking

End

The reason I've only configured one output on port B is purely for testing..once I have this sorted, RB0, RB1, RB2 and RB3 will all be switch inpts, with RB4 - RB7 their coresponding outputs (we have 4 sidings to monitor )

TIA


Malcolm

[Melanie]

Your debounce delay is too short... swap PAUSEUS for a straight PAUSE. 200mS is neither here nor there in the great scheme of a train moving past your reed switch, whereas in 200uS which you have currently, the train would barely have moved a fraction of a millimetre... With some experimentation, you might find that PAUSE 50 will do...

[malc-c]

Thanks for the reply,

I had played with the debounce pause time, but only by a 100's of a uS

I'll increase the delay and see how I get on.

Many thanks

Malcolm

[peterdeco1]

Hi Malcolm. One suggestion is to make all unused ports as outputs. This helps in noisy environments as electric motors drive PIC's crazy even with a separate supply. Make sure portb.0 is held high with a resistor not too high in value. I once had a small hobby motor drive my PIC crazy until I went down to a 1K resistor as a pullup.

CMCON = 7
TRISA = 0
TRISB = 0 'MAKE ALL OUTPUTS
PORTA = 0
PORTB = 0 'ALL OUTPUTS LOW
INPUT PORTB.0 'RB0 SWITCH INPUT

MAIN:
NAP 0 'REDUCE CURRENT DRAIN ON BATTERY
IF PORTB.0 = 0 THEN CHANGELED 'IF REED SWITCH CLOSED CHANGE LED STATE
GOTO MAIN

CHANGELED:
TOGGLE PORTB.4 'CHANGE LED STATE

WAITFORRELEASE:
PAUSE 1000 'WAIT A SECOND
IF PORTB.0 = 0 THEN WAITFORRELEASE 'WAIT HERE FOR REED TO OPEN
GOTO MAIN

[malc-c]

Hi Peter,

Thanks for the advice and I'll make port A all output as I'm only using port B. Oh and yes the inputs on the switches are tied high via a 10K resistor.

[Acetronics2]

Hi,Malc

Have a look to the " BUTTON " command ...it is really very powerful for such application.

Add a DEFINE BUTTON_PAUSE 200 at the top of your program if you want a debounce time of 200 ms ( max 255 ms ...) ... that's all !

read you soon !!!

Alain

PS; if not already done, download this : http://www.melabs.com/downloads/pbpm304.pdf
THE reference manual !!!
Microcode studio : http://www.melabs.com/downloads/mcs2300.zip