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Re: How do you read digital inputs from microswitch, jumpers, dip-switches...?

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On 9/25/18 10:12 AM, Chris wrote:
> On 09/25/18 11:57, Richard Damon wrote:
>> On 9/24/18 11:00 AM, Grant Edwards wrote:
>>> On 2018-09-21, Chris<xxx.syseng.yyy@gfsys.co.uk>  wrote:
>>>> On 09/20/18 10:52, pozz wrote:
>>>>> Often I have digital inputs connected to switches managed by the user.
>>>>> For example: microswitches, tactile switches, push-buttons,
>>>>> dip-switches, simple jumpers and so on.
>>>>>
>>>>> What is your preferred method to read the status of this inputs?
>>>>>
>>>>
>>>>
>>>> Assuming not in an rtos environment, where you have timers,
>>>> a system clock tick and background timer capability, perhaps
>>>> with callback, can make debounce easy.  A simple state
>>>> machine using a switch statement, allows testing the input,
>>>> delaying for a specified time, then reading again before
>>>> acceptance of the change.
>>>
>>> Why delay before accepting the change?
>>>
>>> That sounds like you're trying to ignore noise pulses that appear
>>> spontaneously.  That's a completely different problem from debouncing.
>>>
>>> In my experience, the usual method of debouncing, is to accept the
>>> change immediately then ignore the switch for a period of time (a few
>>> tens of milliseconds is usually sufficient).
>>>
>>
>> For a human, 10s of milliseconds is normally 'instantaneous', so good
>> enough. (In some gaming environment response gets more critical when the
>> user has developed good twitch reflexes). While buttons rarely make a
>> spontaneous make, in some environments they may open momentarily without
>> intentional operation, so ignoring very short signals may be useful.
> 
> Ok, rushed and incomplete description. What I mean is that
> state starts off = idle. On clock tick, input is read and
> compared against the most recent value. If there is no
> change, do nothing. If there is a change, state = pending.
> On next tick, read again and if the same, return new value,
> otherwise state = idle.
> 
> Very simplistic, yes, but using a clock tick to drive such
> code means a keyscanner or hardware input module can run
> in the background at interrupt level. Data from that can
> either use a common variable, or queue...
> 
> Chris

My comment dealt with the fact that for many purposes, that 1-2 clock
tick delay is acceptable because it is 'fast' enough. In some
environments, like gaming, the delay may be unacceptable due to people
working on 'twitch' reflexes. For that sort of environment you need a
slightly more complicated coding which responds immediately to a switch
change, but then doesn't respond if the next sample falls back to the
old state, but delays that reaction for another sample (or two if cheap
bouncy switches). This gives immediate response without a risk of
bouncing. For this case sampling tends to be synchronous with the
display processing, which in some cases may be fast enough to otherwise
detect a bouncing switch. Avoiding a frame delay to denounce may be very
important as often you already have a frame delay from building frame
n+1 while frame n is being displayed to the user, so even instantaneous
reaction without a denounce delay can't affect the screen until frame
n+2. If it didn't happen until n+3, some gamers will notice (they are
actually probably somewhat anticipating), but 'frame perfect' is a thing
for some of them.

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How do you read digital inputs from microswitch, jumpers, dip-switches...? pozz <pozzugno@gmail.com> - 2018-09-20 11:52 +0200
  Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? John Speth <johnspeth@yahoo.com> - 2018-09-20 05:35 -0700
    Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? pozz <pozzugno@gmail.com> - 2018-09-21 09:42 +0200
      Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? David Brown <david.brown@hesbynett.no> - 2018-09-21 11:09 +0200
        Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Grant Edwards <invalid@invalid.invalid> - 2018-09-24 14:53 +0000
          Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? gnuarm.deletethisbit@gmail.com - 2018-09-29 12:34 -0700
      Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Andrew Smallshaw <andrews@sdf.org> - 2018-09-21 09:16 +0000
      Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? gnuarm.deletethisbit@gmail.com - 2018-09-21 06:22 -0700
        Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Robert Wessel <robertwessel2@yahoo.com> - 2018-09-21 10:04 -0500
          Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? lasselangwadtchristensen@gmail.com - 2018-09-21 14:47 -0700
            Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Robert Wessel <robertwessel2@yahoo.com> - 2018-09-22 21:57 -0500
              Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Andrew Smallshaw <andrews@sdf.org> - 2018-09-23 04:55 +0000
              Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? gnuarm.deletethisbit@gmail.com - 2018-09-22 22:55 -0700
          Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? gnuarm.deletethisbit@gmail.com - 2018-09-22 09:27 -0700
          Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Grant Edwards <invalid@invalid.invalid> - 2018-09-24 14:57 +0000
            Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Ed Prochak <edprochak@gmail.com> - 2018-10-05 09:52 -0700
              Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Richard Damon <Richard@Damon-Family.org> - 2018-10-05 14:40 -0400
              Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? gnuarm.deletethisbit@gmail.com - 2018-10-05 12:48 -0700
  Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Robert Wessel <robertwessel2@yahoo.com> - 2018-09-20 23:38 -0500
  Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Chris <xxx.syseng.yyy@gfsys.co.uk> - 2018-09-21 14:43 +0100
    Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Grant Edwards <invalid@invalid.invalid> - 2018-09-24 15:00 +0000
      Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Richard Damon <Richard@Damon-Family.org> - 2018-09-25 06:57 -0400
        Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Chris <xxx.syseng.yyy@gfsys.co.uk> - 2018-09-25 15:12 +0100
          Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Richard Damon <Richard@Damon-Family.org> - 2018-09-28 08:10 -0400
            Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Chris <xxx.syseng.yyy@gfsys.co.uk> - 2018-09-28 15:43 +0100
              Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Richard Damon <Richard@Damon-Family.org> - 2018-09-28 21:23 -0400
              Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Richard Damon <Richard@Damon-Family.org> - 2018-09-28 21:42 -0400
              Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Ed Prochak <edprochak@gmail.com> - 2018-10-05 10:04 -0700

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