Re: Apple II's paddle 3 button

[dalloff@gcfn.org (Dave Althoff Jr)]

Michael J. Mahon (mjmahon@aol.com) wrote:
: Dave Althoff Jr wrote:

: <snip>

: >On a related note...does anyone have any suggestions for the best way to
: >de-bounce the paddle button input?  I've got an IR phototransistor
: >triggering my PB0 input on an old ][e, sensing when the spokes go by on a
: >K'Nex Ferris wheel, but I'm having trouble getting any accuracy out of it
: >because the signal bounces.  And yet, I need fast response...

: Are you sure the problem is bounce?  A phototransistor should faithfully
: sense the instantaneous light level falling on it, and is not subject to
: switch bounce (actual "bouncing" of mechanical contacts, causing noise
: on "make").

: It might be useful to write a short M/L program to sample the button
: input at high speed and record the approximate times between "makes"
: and "breaks".  You might find that some other timing issue is creating
: the problem.

: The general issue of debouncing a switch in software is accomplished
: by:

: 1. Scan until a change is sensed,
: 2. Wait a short period (usually a millisecond or two, depending
:    on the switch characteristics), and
: 3. Re-sample the switch.

: If the resampling shows the same state as the first scan, then it
: is presumed to be a real event, and the bounce has settled.

: It is possible to scan for other events during the waiting period,
: so this can be easily generalized to reading the states of large
: numbers of switches (as in a matrix).  If the full scan takes a
: millisecond or more, then simply finding the same (changed)
: state on two successive scans is equivalent to debouncing.

It is most certainly not a mechanical bounce, as you suggest.  I suspect
the problem is with the edge of the target, complicated further by the
fact that I am shooting through a Ferris wheel structure with *two* spokes
between the emitter and detector.  I'm getting multiple state changes
every time a spoke goes by.  I'm wondering if I should add a cap to the
circuit to slow the hardware response time just a little.

It has been a while since I looked at the program, too.  Conveniently, the
Wheel has 16 seats (identified, of course, as 0-F).  Using the single
detector, I should be able to calculate which seat is approaching the
boarding platform, and even come up with motor control to bring the system
to a smooth stop at each seat.  (I already have a PWM motor control
program...one of the annunciators controls the DC motor switch.  Works
kinda neat!)

I need to get back to work on that thing...!

--Dave Althoff, ][.
-- 
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