Pushbutton-controlled blinking LED

i new arduino programming, , excercise in asynchronous digital i/o, i've extended "blinking led without using delay" tutorial example read input button.  i thought might helpful others.

--randy

/* pushbutton-controlled blinking led
* ----------------------------------
*
* reads pushbutton determine rate @ led should
* blink.  if hold pushbutton down x milliseconds, the
* led blink on , off every x milliseconds.
*
* created 25 september 2006
* randy cox
*
* extension of 1 of tutorial examples
* arduino website (http://www.arduino.cc/en/main/learnarduino):
*
* blinking led without using delay
* --------------------------------
*
* turns on , off light emitting diode(led) connected digital  
* pin, without using delay() function.  this means other code
* can run @ same time without being interrupted led code.
*
* created 14 february 2006
* david a. mellis
* http://arduino.berlios.de
*/

int ledpin = 13;                // led connected digital pin 13
int ledvalue = low;             // previous value of led
long ledstarttime = 0;          // store last time led updated
long ledblinkinterval = 1000;   // interval @ blink (milliseconds)

int buttonpin = 2;              // active-high momentary pushbutton on pin 2
int buttonvalue = high;         // current state of button
long buttonpresstime = 0;       // store time button pressed


void setup()
{
 pinmode(ledpin, output);      // sets digital pin output
}

void loop()
{
 // check see if button pressed.  if so, mark time.  when the
 // button released, calculate how long pressed, , make led
 // blink @ same rate.
 buttonvalue = digitalread(buttonpin);

 // button press
 if (buttonvalue==low && buttonpresstime==0) {
   buttonpresstime = millis();  // capture time of press
 }

 // button release
 if (buttonvalue==high && buttonpresstime!=0) {
   ledblinkinterval = millis() - buttonpresstime;  // set new flash interval
   buttonpresstime = 0;                            // clear button press time
 }

 // check see if it's time blink led; is, difference
 // between current time , last time blinked led bigger than
 // interval @ want blink led.
 if (millis() - ledstarttime > ledblinkinterval) {
   ledstarttime = millis();   // remember last time blinked led

   // if led off turn on , vice-versa.
   if (ledvalue == low)
     ledvalue = high;
   else
     ledvalue = low;

   digitalwrite(ledpin, ledvalue);
 }
}

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