Before reading this tutorial, make sure you have read the How to use our PIC Tutorials page!

This is one of my favorite subroutine! When i design a project, i always try to make the user interface minimal. For this, you need to have to buttons doing more than just one click. This tutorial will demonstrate how to distinguish three different button states. Then, according to how the button was pressed, a different routine shall be executed. The three states are:

• Click: A quick button click, faster than 800mSec
• Double Click: Two clicks within 300mSec with max delay between 150mSec
• Long Press: A long press to the button, longer than 800mSec

The mSec times given are fully parametric and can be changed at will. This is important because it it different if the button is mechanical, different if it is a touch button, different for menu systems and different for critical applications such as light control.

The circuit has one button and three LEDs:

Each LED is lit from another subroutine. The RED LED will light on a single click, the GREEN on a long press and the yellow on a double click.

The code is a little bit complicated, as many parameters needs to be taken into account during a click. Also, some extra delays are added for avoiding false triggers (debounce technique).

; RAM preserved -----------------------------------------------------------
	cblock 0x20
		WaitCounter,WaitCounter2
		IntervalCounter
	endc
; Conastants --------------------------------------------------------------
GLDoubleClick_Interval	=	d'15'	;mSec x 10
GLDoubleClick_MaxDelay	=	d'30'	;mSec x 10
GLLongClick_Interval	=	d'80'	;mSec x 10
; Main Program ------------------------------------------------------------

Start
				bank1				;Go to bank 1
				movlw b'11111111'		;
				movwf TRISA			;Set the port pin types of the RA

				movlw b'11111000'		;
				movwf TRISB			;Set the port pin types of the RB
				bank0				;Go to bank 0

				bcf ClickOutput
				bcf DblClickOutput
				bcf LngClickOutput

MainLoop
				btfss ButtonInput
				goto MainLoop
				
				movlw GLLongClick_Interval
				movwf IntervalCounter
CheckForLongClick
				call Wait10mSec
				btfss ButtonInput		;Check if it is a long click
				goto NoLongClick
				decfsz IntervalCounter,f
				goto CheckForLongClick

				;It WAS a long click
				goto Run_Long_Click

NoLongClick							;It was NOT a long click
				movf  IntervalCounter,w
				sublw GLLongClick_Interval	;Check How many mSeconds was the first keypress

				sublw GLDoubleClick_MaxDelay	;Was it MORE thant the max dbl initial click?
				btfss Carry			;If the result is negative
				goto Run_Single_Click		;Then it was a single click.

				;Else, we will wait more to see if it will be a dbl click
				movlw GLDoubleClick_Interval
				movwf IntervalCounter

CheckForDblgClick
				call Wait10mSec
				btfsc ButtonInput
				goto It_Is_A_Dbl_Click

				decfsz IntervalCounter,f
				goto CheckForDblgClick

				;It WAS a Single click
				goto Run_Single_Click				

It_Is_A_Dbl_Click
				call Wait2mSec
				btfsc ButtonInput
				goto It_Is_A_Dbl_Click		;Wait untill the button is released
				goto Run_Dbl_Click

Run_Single_Click
				bsf ClickOutput
				call Wait1Sec
				bcf ClickOutput
				goto WaitForKeyReleaseBeforeReturn
Run_Dbl_Click
				bsf DblClickOutput
				call Wait1Sec
				bcf DblClickOutput
				goto WaitForKeyReleaseBeforeReturn

Run_Long_Click
				bsf LngClickOutput
				call Wait1Sec
				bcf LngClickOutput
;				goto WaitForKeyReleaseBeforeReturn	;This instrruction is not really nesecary here!

WaitForKeyReleaseBeforeReturn
				call Wait4mSec
				btfsc ButtonInput
				goto WaitForKeyReleaseBeforeReturn
				call Wait10mSec
				goto MainLoop

We start by defining the pin types. Right after, we clear the three outputs so that the LEDs are turned off. The MainLoop this time is... 2 instructions long! It checks if the button is pressed. If not, it loops back to MainLoop. If it is, it will continue with the click type check. Trying to describe this subroutine with words would complicate the things even further. Therefore, i have add the following flow chart that describes only this subroutine:

You can download it also as pdf:

Click type check flow chart

So, after this subroutine, one of the three click-subroutines shall run. It will be either a single, a double or a long click. According to the subroutine call, the corresponding LED shall lit. Also, the LED shall remain ON for one second and then it will turn off again. Then, the program flow shall return back to MainLoop. But before this is done, we need to ensure that the button is not still pressed (for example after a double click that the second click could be still active). Therefore, i have add another small subroutine that is called after every click/dbl click/lng click subroutine execution. This subroutine will check every 4mSec the state of the button. If the button is not pressed, then it will wait another 10mSec (for debouncing) and it will go back to MainLoop.

Following are the files for this project:

PIC Tutorial - A Clever Button

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Basics       What will you need       Choosing the right PICThe MPLAB       Getting familiar with the MPLAB environment       Creating a new project       Open and close projects       Creating new files and including them in the project       Your very first assembly program       Compile a program and transfer to the PICSection 1: Beginner's theoryMemory Organization       The Data Memory Organization       The Program Memory OrganizationThe instructions       General knowledge about instructions       Value Loading Instructions       Program Flow Instructions       Mathematic Instructions       Logic Function Instructions       Bit Orientated Instructions       Byte Orientated Instructions       Miscellaneous InstructionsThe Basic Special Function Registers       The Status Register       The Option_Reg Register       The TRIS and PORT registersBeginner's PIC Tutorials       How to use our PIC Tutorials       A Pushbutton turning an LED on and off       A Simple LED Flasher       Interfacing Multiple Switches - The internal Pull-Up resistors       An LED Sequencer       Interface a Single 7seg Digit       Interface Multiple 7seg Digits       A 3-digits Decimal Counter       A Clever ButtonSection 2: Intermediate theory       Instruction Cycle Duration and Calculated Delays       The Timer Modules - Timer0       The Timer Modules - Timer1       The Timer Modules-Timer2

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