FR: better event detection via dual moving average cross-over

[Andrei-Pozolotin]

1. currently "tare" happens once, on setup: https://github.com/IvDm/Z-probe-on-smd-resistors-2512/blob/master/strain_gage_switch_ATtiny85.ino

2. this does not reflect environment changes during long operation:

   • parameters temperature drift,
   • parameters mechanical creep, etc.

3. a better way is to use dual moving average cross-over approach, and eliminate dependency on environment changes i.e.:

   // detect touch events
   void process_trigger() {
   const int32_t fast = moving_fast.average();
   const int32_t slow = moving_slow.average();
   const int32_t delta = fast - slow;
   if (delta > 0) {  // react only on proper direction
       if (has_trigger) {
           if (delta < DELTA_PASSIVE) {  // detect turn off
               has_trigger = false;  // remember state
               moving_slow.setup(trigger_slow);  // recover to event start
               process_output (LOW);  // issue turn off
               time_passive = millis();  // report event finish
           }
       } else {
           if (delta > DELTA_ACTIVE) {  // detect turn on
               has_trigger = true;  // remember state
               trigger_slow = slow;  // remember till event finish
               process_output (HIGH);  // issue turn on
               time_active = millis();  // report event start
           }
       }
   }
   }

4. here is full sketch for arduino/nano: https://gist.github.com/Andrei-Pozolotin/e7bf413e2438863a04c2497258662bec