✨ PELTIER_BED (MarlinFirmware#27334)

Co-authored-by: Scott Lahteine <[email protected]>

Marlin/Configuration.h

@@ -802,6 +802,40 @@
   //#define BED_LIMIT_SWITCHING   // Keep the bed temperature within BED_HYSTERESIS of the target
 #endif
 
+/**
+ * Peltier Bed - Heating and Cooling
+ *
+ * A Peltier device transfers heat from one side to the other in proportion to the amount of
+ * current flowing through the device and the direction of current flow. So the same device
+ * can both heat and cool.
+ *
+ * When "cooling" in addition to rejecting the heat transferred from the hot side to the cold
+ * side, the dissipated power (voltage * current) must also be rejected. Be sure to set up a
+ * fan that can be powered in sync with the Peltier unit.
+ *
+ * This feature is only set up to run in bang-bang mode because Peltiers don't handle PWM
+ * well without filter circuitry.
+ *
+ * Since existing 3D printers are made to handle relatively high current for the heated bed,
+ * we can use the heated bed power pins to control the Peltier power using the same G-codes
+ * as the heated bed (M140, M190, etc.).
+ *
+ * A second GPIO pin is required to control current direction.
+ * Two configurations are possible: Relay and H-Bridge
+ *
+ * (At this time only relay is supported. H-bridge requires 4 MOS switches configured in H-Bridge.)
+ *
+ * Power is handled by the bang-bang control loop: 0 or 255.
+ * Cooling applications are more common than heating, so the pin states are commonly:
+ *   LOW  = Heating = Relay Energized
+ *   HIGH = Cooling = Relay in "Normal" state
+ */
+//#define PELTIER_BED
+#if ENABLED(PELTIER_BED)
+  #define PELTIER_DIR_PIN           -1  // Relay control pin for Peltier
+  #define PELTIER_DIR_HEAT_STATE   LOW  // The relay pin state that causes the Peltier to heat
+#endif
+
 // Add 'M190 R T' for more gradual M190 R bed cooling.
 //#define BED_ANNEALING_GCODE
 

Marlin/Configuration_adv.h

@@ -203,7 +203,7 @@
 //
 #if DISABLED(PIDTEMPBED)
   #define BED_CHECK_INTERVAL 5000   // (ms) Interval between checks in bang-bang control
-  #if ENABLED(BED_LIMIT_SWITCHING)
+  #if ANY(BED_LIMIT_SWITCHING, PELTIER_BED)
     #define BED_HYSTERESIS 2        // (°C) Only set the relevant heater state when ABS(T-target) > BED_HYSTERESIS
   #endif
 #endif

Marlin/src/inc/Conditionals-5-post.h

@@ -3039,7 +3039,7 @@
 #endif
 
 /**
- * Heated bed requires settings
+ * Heated Bed required settings
  */
 #if HAS_HEATED_BED
   #ifndef MIN_BED_POWER
@@ -3049,6 +3049,14 @@
     #define MAX_BED_POWER 255
   #endif
   #define WRITE_HEATER_BED(v) WRITE(HEATER_BED_PIN, (v) ^ ENABLED(HEATER_BED_INVERTING))
+  #if ENABLED(PELTIER_BED)
+   /**
+    * A "Heated Bed" Peltier device needs a direction (heat/cool) to be
+    * implemented by a relay (single pin) or H-bridge (2 or 4 pin).
+    * H-Bridge can also perform PWM. (Not recommended for Peltier devices).
+    */
+    #define WRITE_PELTIER_DIR(v) WRITE(PELTIER_DIR_PIN, (v) ? PELTIER_DIR_HEAT_STATE : !PELTIER_DIR_HEAT_STATE)
+  #endif
 #endif
 
 /**

Marlin/src/inc/Warnings.cpp

@@ -921,3 +921,10 @@
 #if defined(ARDUINO_ARCH_HC32) && F_CPU == 200000000
   #warning "HC32 clock is assumed to be 200MHz. If this isn't the case for your board please submit a report so we can add support."
 #endif
+
+/**
+ * Peltier with PIDTEMPBED
+ */
+#if ALL(PELTIER_BED, PIDTEMPBED)
+  #warning "PELTIER_BED with PIDTEMPBED requires extra circuitry. Use with caution."
+#endif

Marlin/src/module/temperature.cpp

@@ -1882,7 +1882,7 @@ void Temperature::mintemp_error(const heater_id_t heater_id OPTARG(ERR_INCLUDE_T
       static bool last_pause_state;
     #endif
 
-    do {
+    do { // 'break' out of this block
 
       #if DISABLED(PIDTEMPBED)
         if (PENDING(ms, next_bed_check_ms)
@@ -1908,38 +1908,63 @@ void Temperature::mintemp_error(const heater_id_t heater_id OPTARG(ERR_INCLUDE_T
         constexpr bool bed_timed_out = false;
       #endif
 
-      if (!bed_timed_out) {
-        if (is_bed_preheating()) {
-          temp_bed.soft_pwm_amount = MAX_BED_POWER >> 1;
-        }
-        else {
-          #if ENABLED(PIDTEMPBED)
-            temp_bed.soft_pwm_amount = WITHIN(temp_bed.celsius, BED_MINTEMP, BED_MAXTEMP) ? (int)get_pid_output_bed() >> 1 : 0;
-          #else
-            // Check if temperature is within the correct band
-            if (WITHIN(temp_bed.celsius, BED_MINTEMP, BED_MAXTEMP)) {
-              #if ENABLED(BED_LIMIT_SWITCHING)
+      if (bed_timed_out) break;
+
+      if (is_bed_preheating()) {
+        temp_bed.soft_pwm_amount = MAX_BED_POWER >> 1;
+        break;
+      }
 
-                // Range-limited "bang-bang" bed heating
-                if (temp_bed.is_above_target(BED_HYSTERESIS))
-                  temp_bed.soft_pwm_amount = 0;
-                else if (temp_bed.is_below_target(BED_HYSTERESIS))
-                  temp_bed.soft_pwm_amount = MAX_BED_POWER >> 1;
+      #if ENABLED(PIDTEMPBED)
 
-              #else // !PIDTEMPBED && !BED_LIMIT_SWITCHING
+        //
+        // PID Bed Heating
+        //
+        temp_bed.soft_pwm_amount = WITHIN(temp_bed.celsius, BED_MINTEMP, BED_MAXTEMP) ? (int)get_pid_output_bed() >> 1 : 0;
 
-                // Simple (noisy) "bang-bang" bed heating
-                temp_bed.soft_pwm_amount = temp_bed.is_below_target() ? MAX_BED_POWER >> 1 : 0;
+      #else // !PIDTEMPBED
 
-              #endif
-            }
-            else {
+        //
+        // Range-limited "bang-bang" bed heating
+        //
+
+        // Bed Off if the current bed temperature is outside the allowed range
+        if (!WITHIN(temp_bed.celsius, BED_MINTEMP, BED_MAXTEMP)) {
+          temp_bed.soft_pwm_amount = 0;
+          WRITE_HEATER_BED(LOW);
+          break;
+        }
+
+        #if ENABLED(PELTIER_BED)
+          /**
+           * Peltier bang-bang maintains max bed power but changes
+           * current direction to switch between heating/cooling.
+           */
+          if (temp_bed.target && temp_bed.is_above_target(BED_HYSTERESIS)) {  // Fast Cooling
+            temp_bed.soft_pwm_amount = MAX_BED_POWER;
+            temp_bed.peltier_dir_heating = false;
+          }
+          else if (temp_bed.is_below_target(BED_HYSTERESIS)) {                // Heating
+            temp_bed.soft_pwm_amount = MAX_BED_POWER;
+            temp_bed.peltier_dir_heating = true;
+          }
+          else
+            temp_bed.soft_pwm_amount = 0;                                     // Off (ambient cooling)
+
+        #else // !PELTIER_BED
+
+          #if ENABLED(BED_LIMIT_SWITCHING)
+            if (temp_bed.is_above_target(BED_HYSTERESIS))       // Cooling (implicit off)
               temp_bed.soft_pwm_amount = 0;
-              WRITE_HEATER_BED(LOW);
-            }
+            else if (temp_bed.is_below_target(BED_HYSTERESIS))  // Heating
+              temp_bed.soft_pwm_amount = MAX_BED_POWER >> 1;
+          #else                                                 // Not bed limit switching
+            temp_bed.soft_pwm_amount = temp_bed.is_below_target() ? MAX_BED_POWER >> 1 : 0;
           #endif
-        }
-      }
+
+        #endif // !PELTIER_BED
+
+      #endif // !PIDTEMPBED
 
     } while (false);
   }
@@ -2945,6 +2970,10 @@ void Temperature::init() {
   #endif
 
   #if HAS_HEATED_BED
+    #if ENABLED(PELTIER_BED)
+      SET_OUTPUT(PELTIER_DIR_PIN);
+      OUT_WRITE(PELTIER_DIR_PIN, !PELTIER_DIR_HEAT_STATE);
+    #endif
     #ifdef BOARD_OPENDRAIN_MOSFETS
       OUT_WRITE_OD(HEATER_BED_PIN, ENABLED(HEATER_BED_INVERTING));
     #else
@@ -3926,6 +3955,9 @@ void Temperature::isr() {
 
       #if HAS_HEATED_BED
         _PWM_MOD(BED, soft_pwm_bed, temp_bed);
+        #if ENABLED(PELTIER_BED)
+          WRITE_PELTIER_DIR(temp_bed.peltier_dir_heating);
+        #endif
       #endif
 
       #if HAS_HEATED_CHAMBER
@@ -4392,15 +4424,15 @@ void Temperature::isr() {
 #if HAS_TEMP_SENSOR
   /**
    * Print a single heater state in the form:
-   *        Bed: " B:nnn.nn /nnn.nn"
-   *    Chamber: " C:nnn.nn /nnn.nn"
-   *      Probe: " P:nnn.nn"
-   *     Cooler: " L:nnn.nn /nnn.nn"
-   *      Board: " M:nnn.nn"
-   *        SoC: " S:nnn.nn"
-   *  Redundant: " R:nnn.nn /nnn.nn"
-   *   Extruder: " T0:nnn.nn /nnn.nn"
-   *   With ADC: " T0:nnn.nn /nnn.nn (nnn.nn)"
+   *     Extruder: " T0:nnn.nn /nnn.nn"
+   *          Bed: " B:nnn.nn /nnn.nn"
+   *      Chamber: " C:nnn.nn /nnn.nn"
+   *       Cooler: " L:nnn.nn /nnn.nn"
+   *        Probe: " P:nnn.nn"
+   *        Board: " M:nnn.nn"
+   *          SoC: " S:nnn.nn"
+   *    Redundant: " R:nnn.nn /nnn.nn"
+   *     With ADC: " T0:nnn.nn /nnn.nn (nnn.nn)"
    */
   static void print_heater_state(const heater_id_t e, const_celsius_float_t c, const_celsius_float_t t
     OPTARG(SHOW_TEMP_ADC_VALUES, const float r)
@@ -4418,12 +4450,12 @@ void Temperature::isr() {
       #if HAS_TEMP_CHAMBER
         case H_CHAMBER: k = 'C'; break;
       #endif
-      #if HAS_TEMP_PROBE
-        case H_PROBE: k = 'P'; show_t = false; break;
-      #endif
       #if HAS_TEMP_COOLER
         case H_COOLER: k = 'L'; break;
       #endif
+      #if HAS_TEMP_PROBE
+        case H_PROBE: k = 'P'; show_t = false; break;
+      #endif
       #if HAS_TEMP_BOARD
         case H_BOARD: k = 'M'; show_t = false; break;
       #endif
@@ -4450,6 +4482,17 @@ void Temperature::isr() {
     delay(2);
   }
 
+  /**
+   * Print all heater states followed by power data on a single line.
+   * See print_heater_state for heater output strings.
+   * Power output strings are in the format:
+   *     Extruder: " @:nnn"
+   *          Bed: " B@:nnn"
+   *      Peltier: " P@:H/C"
+   *      Chamber: " C@:nnn"
+   *       Cooler: " L@:nnn"
+   *      Hotends: " @0:nnn @1:nnn ..."
+   */
   void Temperature::print_heater_states(const int8_t target_extruder
     OPTARG(HAS_TEMP_REDUNDANT, const bool include_r/*=false*/)
   ) {
@@ -4481,15 +4524,10 @@ void Temperature::isr() {
       HOTEND_LOOP() print_heater_state((heater_id_t)e, degHotend(e), degTargetHotend(e) OPTARG(SHOW_TEMP_ADC_VALUES, rawHotendTemp(e)));
     #endif
     SString<100> s(F(" @:"), getHeaterPower((heater_id_t)target_extruder));
-    #if HAS_HEATED_BED
-      s.append(" B@:", getHeaterPower(H_BED));
-    #endif
-    #if HAS_HEATED_CHAMBER
-      s.append(" C@:", getHeaterPower(H_CHAMBER));
-    #endif
-    #if HAS_COOLER
-      s.append(" C@:", getHeaterPower(H_COOLER));
-    #endif
+    TERN_(HAS_HEATED_BED,     s.append(F(" B@:"), getHeaterPower(H_BED)));
+    TERN_(PELTIER_BED,        s.append(F(" P@:"), temp_bed.peltier_dir_heating ? 'H' : 'C'));
+    TERN_(HAS_HEATED_CHAMBER, s.append(F(" C@:"), getHeaterPower(H_CHAMBER)));
+    TERN_(HAS_COOLER,         s.append(F(" L@:"), getHeaterPower(H_COOLER)));
     #if HAS_MULTI_HOTEND
       HOTEND_LOOP() s.append(F(" @"), e, ':', getHeaterPower((heater_id_t)e));
     #endif

Marlin/src/module/temperature.h

@@ -437,6 +437,9 @@ typedef struct HeaterInfo : public TempInfo {
   uint8_t soft_pwm_amount;
   bool is_below_target(const celsius_t offs=0) const { return (target - celsius > offs); } // celsius < target - offs
   bool is_above_target(const celsius_t offs=0) const { return (celsius - target > offs); } // celsius > target + offs
+  #if ENABLED(PELTIER_BED)
+    bool peltier_dir_heating; // = false
+  #endif
 } heater_info_t;
 
 // A heater with PID stabilization