detecting switch release.

[jmgelba]

Greetings all,

I'm trying to get a push button switch to only increment a variable on release. I've tried a few.loops but can't seem to get it working right. Anyone have a code sample I can pick over?

Thanks.

[mackrackit]

Look up interrupt on change in you chips data sheet.

[peterdeco1]

Try this

input portb.0 'input with pullup resistor
clear 'all variables = 0

start:
if portb.0 = 1 then start 'stay here until pushbutton pushed

waitforrelease:
if portb.0 =1 then pause 50 ‘debounce
if portb.0 = 0 then waitforrelease 'stay here until button released
let (your variable) = (your variable + 1) 'button released
goto start 'wait for another push

[Mike, K8LH]

I would recommend using a switch state latch bit and simple logic to filter out all but a "new press" or "new release" state without having to wait for the opposite state. You didn't mention if you're using active-low or active-high switch signals so I'll provide (C code) examples for both using parallel switch state logic (below).

   /*
    *  K8LH parallel switch state logic
    *
    *  sample active lo switches with a "new press" filter or
    *  sample active hi switches with a "new release" filter
    *
    *  swnew  ___---___---___---___  sample switches
    *  swold  ____---___---___---__  switch state latch
    *  swnew  ___-__-__-__-__-__-__  changes, press or release
    *  swnew  ___-_____-_____-_____  filter for desired state
    *  flags  ___------______------  toggle flag bits for main
    *
    */
    swnew = ~portb;               // sample active lo switches
    swnew ^= swold;               // changes, press or release
    swold ^= swnew;               // update switch state latch
    swnew &= swold;               // filter for desired state
    flags ^= swnew;               // toggle flag bits for main

   /*
    *  K8LH parallel switch state logic
    *
    *  sample active hi switches with a "new press" filter or
    *  sample active lo switches with a "new release" filter
    *
    *  swnew  ___---___---___---___  sample switches
    *  swold  ____---___---___---__  switch state latch
    *  swnew  ___-__-__-__-__-__-__  changes, press or release
    *  swnew  ___-_____-_____-_____  filter for desired state
    *  flags  ___------______------  toggle flag bits for main
    *
    */
    swnew = portb;                // sample active lo switches
    swnew ^= swold;               // changes, press or release
    swold ^= swnew;               // update switch state latch
    swnew &= swold;               // filter for desired state
    flags ^= swnew;               // toggle flag bits for main

Execute this code in an ISR or in a main program loop at some "debounce" interval, typically 10 to 20 milliseconds. Test "flags" bit 4 in the main program for a "new press" or "new release", whichever you're using, for the switch connected to RB4. Clear the flag bit after using it.

To emulate a toggle switch, where you press a switch to toggle its flag from on-to-off or from off-to-on, simply test the flag bit for that switch without clearing the flag afterwards.

The switch state latch variable (swold) represents the real time (plus debounce interval) debounced state of the switches on portb and can be used for selective "repeat" key operation, if desired.

Good luck with your project and Happy Holidays to everyone.

Cheerful regards, Mike

[jmgelba]

Thank you for the responses. I now have a functioning routine and everything is working perfectly.

On to the next issue: how to display text on an LCD from a word or byte.

[mackrackit]

Have you seen the LCDOUT command?