Ignore spurious MAX31855K / 6675 thermocouple errors (#18039)

Marlin/Configuration_adv.h

@@ -39,6 +39,19 @@
 //=============================Thermal Settings  ============================
 //===========================================================================
 
+/**
+ * Thermocouple sensors are quite sensitive to noise.  Any noise induced in
+ * the sensor wires, such as by stepper motor wires run in parallel to them,
+ * may result in the thermocouple sensor reporting spurious errors.  This
+ * value is the number of errors which can occur in a row before the error
+ * is reported.  This allows us to ignore intermittent error conditions while
+ * still detecting an actual failure, which should result in a continuous
+ * stream of errors from the sensor.
+ * 
+ * Set this value to 0 to fail on the first error to occur.
+ */
+#define THERMOCOUPLE_MAX_ERRORS 15
+
 //
 // Custom Thermistor 1000 parameters
 //

Marlin/src/module/temperature.cpp

@@ -2060,6 +2060,10 @@ void Temperature::disable_all_heaters() {
 
 #if HAS_MAX6675
 
+  #ifndef THERMOCOUPLE_MAX_ERRORS
+    #define THERMOCOUPLE_MAX_ERRORS 15
+  #endif
+
   int Temperature::read_max6675(
     #if COUNT_6675 > 1
       const uint8_t hindex
@@ -2072,6 +2076,8 @@ void Temperature::disable_all_heaters() {
       static uint16_t max6675_temp_previous[COUNT_6675] = { 0 };
     #endif
     
+    static uint8_t max6675_errors[COUNT_6675] = { 0 };
+
     #define MAX6675_HEAT_INTERVAL 250UL
 
     #if ENABLED(MAX6675_IS_MAX31855)
@@ -2144,6 +2150,8 @@ void Temperature::disable_all_heaters() {
     WRITE_MAX6675(HIGH); // disable TT_MAX6675
 
     if (max6675_temp & MAX6675_ERROR_MASK) {
+      max6675_errors[hindex] += 1;
+      if (max6675_errors[hindex] > THERMOCOUPLE_MAX_ERRORS) {
         SERIAL_ERROR_START();
         SERIAL_ECHOPGM("Temp measurement error! ");
         #if MAX6675_ERROR_MASK == 7
@@ -2169,8 +2177,14 @@ void Temperature::disable_all_heaters() {
           #endif
         );
       }
-    else
+      else {
         max6675_temp >>= MAX6675_DISCARD_BITS;
+      }
+    }
+    else {
+      max6675_temp >>= MAX6675_DISCARD_BITS;
+      max6675_errors[hindex] = 0;
+    }
 
     #if ENABLED(MAX6675_IS_MAX31855)
       if (max6675_temp & 0x00002000) max6675_temp |= 0xFFFFC000; // Support negative temperature