✨ PELTIER_BED

MarlinFirmware/Marlin#27334

config/examples/TinyBoy2/Configuration.h

@@ -844,6 +844,40 @@
   //#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