Here's my try:
Connect a SPST N.O. momentary from pin 8 to GND with no resistor.
Connect an LED from pin 9 to an LED in series with a current-limiting resistor (220 to 330 ohm) to GND.
My code:
int but = 8;
int led = 9;
int val = 0;
void setup()
{
pinMode(but, INPUT_PULLUP);
pinMode(led, OUTPUT); // not needed, but I like to be explicit
}
void loop()
{
if(digitalRead(but) == LOW)
{
//here: the button is pushed
val += 20; // increment the brightness of the LED by 1/24th
val = min(val, 255); // maximum PWM value is 255
}
else
{
//here: the button has been released
val = 0; // turn the LED OFF
}
analogWrite(led,val); // adjust the PWM
delay( 250 ); // give yourself a chance to see the result
}
should take about 3 seconds from OFF to full brightness. If you need it to be quicker, adjust the delay time
the delay also tends to debounce the switch too