Subject:
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Re: How2 'count' in NQC
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 3 Nov 2000 06:03:08 GMT
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Original-From:
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Steve Baker <sjbaker1@airmail#Spamless#.net>
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Reply-To:
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sjbaker1@%nomorespam%airmail.net
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Viewed:
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737 times
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Jerry Kalpin wrote:
> I have spent about 4 hours discovering that a touch sensor can count many
> times where you expect it to count *once*.
The sensor returns 1 for as long as it's held down.
In your code:
> #define BUMPER SENSOR_2
> #define LAMP OUT_B
> #define FLASH_TIME 10
> #define DELAY 50
>
> int counter;
>
> void check_switch()
> {
> if (BUMPER == 1)
> {
> counter += 1;
> Wait (DELAY); //to register 1 count only
> }
> }
You are actually counting how long the switch is held down - in units of about
a half second. So if you press and hold the switch for ten seconds, you'll get
a count of about 20 in 'counter.
Perhaps you want this:
int last_bumper_state ;
int counter ;
void check_switch ()
{
int bumper_state ;
bumper_state = BUMPER ;
if ( last_bumper_state == 0 && bumper_state == 1 )
counter++ ;
last_bumper_state = bumper_state ;
}
...this will now count only when the routine sees that the last time it was called,
the bumper was NOT pushed - but now it IS pushed. Hence the counter will count just
once when you push the button - and not change again until you release the button and
then press it a second time.
> void check_counter()
> {
> if (counter > 5) //light flashes after the 6th actuation
> {
> On (LAMP);
> counter = 0;
> Wait (FLASH_TIME);
> Off (LAMP);
> }
> }
It's better to try to avoid delays like this since while this task is
delaying, it can't be doing anything else. If someone pressed the
button (and immediately released it again) while you were in
"Wait(FLASH_TIME);" then you'd miss it!
A better solution would be this program:
#define BUMPER SENSOR_2
#define LAMP OUT_B
#define FLASH_TIME 100
int last_bumper_state ;
int counter ;
int lamp_time_left ;
void check_switch ()
{
int new_bumper_state ;
new_bumper_state = BUMPER ;
if ( last_bumper_state == 0 && new_bumper_state == 1 )
counter++ ;
last_bumper_state = new_bumper_state ;
}
void update_lamp ()
{
if ( counter > 5 ) //light flashes after the 6th actuation
{
On ( LAMP ) ;
lamp_time_left = FLASH_TIME ;
counter = 0 ;
}
else
if ( lamp_time_left < 1 )
Off ( LAMP ) ;
else
lamp_time_left -- ;
}
task main()
{
counter = 0 ;
last_bumper_state = 0 ;
lamp_time_left = 0 ;
SetSensor ( BUMPER, SENSOR_TOUCH ) ;
while ( true )
{
check_switch () ;
update_lamp () ;
Wait ( 1 ) ;
}
}
This program will flash the lamp on for a whole second after every sixth
sensor press...but it won't miss *any* sensor presses unless they are less
than 1/100th second in duration.
Actually, an even easier way would be to run two tasks at once - one
monitoring the switch and the other flashing the light.
#define BUMPER SENSOR_2
#define LAMP OUT_B
#define FLASH_TIME 100
int last_bumper_state ;
int counter ;
void check_switch ()
{
int new_bumper_state ;
new_bumper_state = BUMPER ;
if ( last_bumper_state == 0 && new_bumper_state == 1 )
counter++ ;
last_bumper_state = new_bumper_state ;
}
task update_lamp ()
{
while ( true )
{
if ( counter > 5 ) //light flashes after the 6th actuation
{
counter = 0 ;
On ( LAMP ) ;
Wait ( FLASH_TIME ) ;
Off ( LAMP ) ;
}
else
Wait ( 1 ) ;
}
}
task main()
{
counter = 0 ;
last_bumper_state = 0 ;
SetSensor ( BUMPER, SENSOR_TOUCH ) ;
start update_lamp () ;
while ( true )
check_switch () ;
}
This should be even better than the previous program because the time-critical
switch testing loop has no delays in it at all.
Anyway, there are yet more levels of sophistication that could be employed if you
truly utterly *had* to flash the light *EXACTLY* on every sixth push for even VERY
short/rapid clicks...however, events that short are rare with physical/mechanical
systems such as are found in Lego robots.
--
Steve Baker HomeEmail: <sjbaker1@airmail.net>
WorkEmail: <sjbaker@link.com>
HomePage : http://web2.airmail.net/sjbaker1
Projects : http://plib.sourceforge.net
http://tuxaqfh.sourceforge.net
http://tuxkart.sourceforge.net
http://prettypoly.sourceforge.net
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Message has 2 Replies:
 | | Re: How2 'count' in NQC
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| Steve, this is the third time you have helped me, and this time you obviously spent a lot of time working out the alternatives. First of all, the Wait (DELAY); in my inept code was not to flash every half second. It was to prevent additional counts (...) (24 years ago, 3-Nov-00, to lugnet.robotics)
| | | Re: How2 'count' in NQC
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| I have noticed this ongoing thread about the difficulties of debouncing and counting switch closures, and I must say that it is a very real problem anywhere electromechanical switches are interfaced to electronics which is orders of magnitude (...) (24 years ago, 3-Nov-00, to lugnet.robotics)
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Message is in Reply To:
| | How2 'count' in NQC
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| In NQC you count by adding 1 to a variable like this: int counter; counter += 1 But it's hard to know *how much* you have counted; however, you can build a little program to (say) flash a light when you reach a certain count. I have spent about 4 (...) (24 years ago, 2-Nov-00, to lugnet.robotics)
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