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-   -   LimitSwitch as Command Button (http://www.chiefdelphi.com/forums/showthread.php?t=112359)

notmattlythgoe 30-01-2013 11:07
LimitSwitch as Command Button
 
Is there a way to set a command to fire on the push of a limit switch in a similar way to the way joystick buttons are linked to commands?

BigJ 30-01-2013 12:02
Re: LimitSwitch as Command Button
 
there is a subclass of Button called DigitalIOButton that should do what you want.

notmattlythgoe 30-01-2013 12:16
Re: LimitSwitch as Command Button
 
Quote:
Originally Posted by BigJ (Post 1224509)
there is a subclass of Button called DigitalIOButton that should do what you want.
Awesome, I knew it was somewhere but I couldn't find it. Thank you.

Joe Ross 30-01-2013 12:16
Re: LimitSwitch as Command Button
 
Quote:
Originally Posted by BigJ (Post 1224509)
there is a subclass of Button called DigitalIOButton that should do what you want.
That is designed for a driver station digital i/o, not on the robot. To do it on the robot, it would not be hard to create a class to extend Button that reads from a digital i/o on the robot. Alternately, you could create an InternalButton object and periodically call the setPressed method with the state of the limit switch.

notmattlythgoe 30-01-2013 12:24
Re: LimitSwitch as Command Button
 
Quote:
Originally Posted by Joe Ross (Post 1224516)
That is designed for a driver station digital i/o, not on the robot. To do it on the robot, it would not be hard to create a class to extend Button that reads from a digital i/o on the robot. Alternately, you could create an InternalButton object and periodically call the setPressed method with the state of the limit switch.
My only worry is getting multiple triggers with one press from noise on the channel. We're trying to implement a frisbee counter that count frisbees coming in and leaving the robot. We tried using the Counter class, but we kept getting random increases in the count from the limit switches. I'm assuming there was noise as the switch was pressed which made it think that there were multiple presses.

BigJ 30-01-2013 12:46
Re: LimitSwitch as Command Button
 
Whoops, my bad. Yeah you should be able to extend Button then and use your own like Joe said. If you only want one activation in a certain amount of time you could make a Timer object internal to your class to make sure only one activation happens per amount of time.

Joe Ross 30-01-2013 12:48
Re: LimitSwitch as Command Button
 
Quote:
Originally Posted by notmattlythgoe (Post 1224522)
My only worry is getting multiple triggers with one press from noise on the channel. We're trying to implement a frisbee counter that count frisbees coming in and leaving the robot. We tried using the Counter class, but we kept getting random increases in the count from the limit switches. I'm assuming there was noise as the switch was pressed which made it think that there were multiple presses.
The counter class acts as an interrupt and counts every single edge of the switch bounce, which isn't what you want.

The simplest method for dealing with switch bounce is to poll the switch slower then the duration of the switch bounce. This works as long as the process actuating the switch is "slow", which my guess is that a frisbee counter is. For example, if the switch bounces for 10ms, polling it every 20ms will give you at worst one reading during switch bounce. If you happen to sample low during the bounce, you're reading of the switch will be delayed 20ms (the next sample will be high). If you happen to sample high during the switch bounce, you will react immediately (and the next sample will be high). If you extend button to read the switch, it would automatically get called at 20ms.

The following paper has lots of examples of switch bounce, as well as examples of both hardware and software debouncing, if you determine you do need to debounce. http://www.eng.utah.edu/~cs5780/debouncing.pdf

If you extend Button, you could implement your debouncing algorithm in get method.

gixxy 30-01-2013 12:51
Re: LimitSwitch as Command Button
 
It is quite easy actually. You just extend Button and implement your own get() method to return the limit switch input. Add your own debouncing and you are good.

Here is my code (I haven't implemented any debouncing)

Code:
/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package edu.wpi.first.frc3946.MyTest;

import edu.wpi.first.wpilibj.DigitalInput;
import edu.wpi.first.wpilibj.buttons.Button;

/**
 *
 * @author Gustave Michel
 */
public class IOButton extends Button {
    DigitalInput button;
   
    public IOButton(int port) {
        button = new DigitalInput(port);
    }
   
    public boolean get() {
        return button.get();
    }
   
}

notmattlythgoe 30-01-2013 12:52
Re: LimitSwitch as Command Button
 
Quote:
Originally Posted by Joe Ross (Post 1224538)
The counter class acts as an interrupt and counts every single edge of the switch bounce, which isn't what you want.

The simplest method for dealing with switch bounce is to poll the switch slower then the duration of the switch bounce. This works as long as the process actuating the switch is "slow", which my guess is that a frisbee counter is. For example, if the switch bounces for 10ms, polling it every 20ms will give you at worst one reading during switch bounce. If you happen to sample low during the bounce, you're reading of the switch will be delayed 20ms (the next sample will be high). If you happen to sample high during the switch bounce, you will react immediately (and the next sample will be high). If you extend button to read the switch, it would automatically get called at 20ms.

The following paper has lots of examples of switch bounce, as well as examples of both hardware and software debouncing, if you determine you do need to debounce. http://www.eng.utah.edu/~cs5780/debouncing.pdf

If you extend Button, you could implement your debouncing algorithm in get method.
You can set the Counter class up to only read the leading or trailing edges, so that isn't a worry. We'll probably end up extending the Button class and doing it that way. We might end up with IR pairs as the counters so the Button class would give us the most flexibility. Thanks for the info.

notmattlythgoe 01-02-2013 08:11
Re: LimitSwitch as Command Button
 
Thanks guys, overriding the Button class worked great, and there was no bouncing at all. The thread must process slower than the bounce happens so we didn't have to worry about it.


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