Help with signal conditioning

Using Arduino Sensors
3 
if (derivative > 0) Serial.println(100);
  else Serial.println(0);

you can of course also use newval in this comparison to suppress some noise.

if (derivative > 0  && newval > 40) Serial.println(100);
  else Serial.println(0);

Multiple analog reads and averaging them also suppresses some noise of the ADC (==analogRead().
I often average 4, 8 or 16 reads as this divides fast.