Slow PWM fan @ 62.5Hz

Firmware/Configuration.h

@@ -477,7 +477,8 @@ your extruder heater takes 2 minutes to hit the target on heating.
 // Use software PWM to drive the fan, as for the heaters. This uses a very low frequency
 // which is not ass annoying as with the hardware PWM. On the other hand, if this frequency
 // is too low, you should also increment SOFT_PWM_SCALE.
-//#define FAN_SOFT_PWM
+#define FAN_SOFT_PWM
+#define FAN_SOFT_PWM_BITS 4 //PWM bit resolution = 4bits, freq = 62.5Hz
 
 // Incrementing this by 1 will double the software PWM frequency,
 // affecting heaters, and the fan if FAN_SOFT_PWM is enabled.

Firmware/temperature.cpp

@@ -1024,7 +1024,7 @@ void tp_init()
     setPwmFrequency(FAN_PIN, 1); // No prescaling. Pwm frequency = F_CPU/256/8
     #endif
     #ifdef FAN_SOFT_PWM
-    soft_pwm_fan = fanSpeedSoftPwm / 2;
+    soft_pwm_fan = fanSpeedSoftPwm / (1 << (8 - FAN_SOFT_PWM_BITS));
     #endif
   #endif
 
@@ -1600,11 +1600,14 @@ ISR(TIMER0_COMPB_vect)
     soft_pwm_b = soft_pwm_bed;
     if(soft_pwm_b > 0) WRITE(HEATER_BED_PIN,1); else WRITE(HEATER_BED_PIN,0);
 #endif
+  }
 #ifdef FAN_SOFT_PWM
-    soft_pwm_fan = fanSpeedSoftPwm / 2;
+  if ((pwm_count & ((1 << FAN_SOFT_PWM_BITS) - 1)) == 0)
+  {
+    soft_pwm_fan = fanSpeedSoftPwm / (1 << (8 - FAN_SOFT_PWM_BITS));
     if(soft_pwm_fan > 0) WRITE(FAN_PIN,1); else WRITE(FAN_PIN,0);
-#endif
   }
+#endif
   if(soft_pwm_0 < pwm_count)
   { 
     WRITE(HEATER_0_PIN,0);
@@ -1623,7 +1626,7 @@ ISR(TIMER0_COMPB_vect)
   if(soft_pwm_b < pwm_count) WRITE(HEATER_BED_PIN,0);
 #endif
 #ifdef FAN_SOFT_PWM
-  if(soft_pwm_fan < pwm_count) WRITE(FAN_PIN,0);
+  if (soft_pwm_fan < (pwm_count & ((1 << FAN_SOFT_PWM_BITS) - 1))) WRITE(FAN_PIN,0);
 #endif
   
   pwm_count += (1 << SOFT_PWM_SCALE);
@@ -1810,8 +1813,8 @@ ISR(TIMER0_COMPB_vect)
 #endif
   
 #ifdef FAN_SOFT_PWM
-  if (pwm_count == 0){
-    soft_pwm_fan = fanSpeedSoftPwm / 2;
+  if ((pwm_count & ((1 << FAN_SOFT_PWM_BITS) - 1)) == 0)
+    soft_pwm_fan = fanSpeedSoftPwm / (1 << (8 - FAN_SOFT_PWM_BITS));
     if (soft_pwm_fan > 0) WRITE(FAN_PIN,1); else WRITE(FAN_PIN,0);
   }
   if (soft_pwm_fan < pwm_count) WRITE(FAN_PIN,0);