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What's the best way to write this code?

 
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david90



Joined: 25 Feb 2006
Posts: 23

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What's the best way to write this code?
PostPosted: Tue Nov 25, 2008 1:57 am     Reply with quote
I'm using PIC16F676 so I have limited resources.

What I'm trying to make is a digital lock that has 4 buttons. 3 buttons are used to enter the code and the last button is used as an "unlock" button.

One of the features that I want to do is when you hold the "unlock" button for 5 sec, the circuit will go into code change mode where you can change your unlock code.

What's the best way to detect when a user holds down the unlock button for 5 sec or more? I can't dedicate a timer to this feature.
RLScott



Joined: 10 Jul 2007
Posts: 465

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Re: What's the best way to write this code?
PostPosted: Tue Nov 25, 2008 7:39 am     Reply with quote
david90 wrote:
I'm using PIC16F676 so I have limited resources.

What I'm trying to make is a digital lock that has 4 buttons. 3 buttons are used to enter the code and the last button is used as an "unlock" button.

One of the features that I want to do is when you hold the "unlock" button for 5 sec, the circuit will go into code change mode where you can change your unlock code.

What's the best way to detect when a user holds down the unlock button for 5 sec or more? I can't dedicate a timer to this feature.

First you must consider debouncing. If the code has nothing else to do when buttons are pushed, then you can poll for buttons and busy-wait whenever a button is pressed. During the busy-wait, you can use instruction timing or a hardware timer to determine how low a button is held down. Integrate debouncing into that busy-wait so that when a button is first detected as pressed or released, the press or release recognition should be delayed until the press or release has continued for a certain minimum period. A good way to do this is to increment a variable with a ceiling limit whenever the button is detected as pressed and decrement that variable with a floor limit whenever the button is detected as released. When the variable hits the ceiling or the floor you can take whatever recognition action is required.
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