I'm trying to add a cooling fan on PWM but it doesn't work. The yellow graph is the PWM signal (50% duty cycle and period \$3\tau=30ms\$) and the purple one is the speed of the motor. They only make this noise when not running on 100% fan speed. Also, If i turn up the fan speed on the ramps when running a print, nothing. The PWM period is now \$0.1\tau=1ms\$ and duty cycle is still 50%. 50% 24v pwm is not the same as 50% 12v pwm. So in theory we could run. The following is my code for the fan that is at the bottom of your config.h . Now let's increase the PWM frequency. THE PROBLEM: on my board the pin dedicated to regulate the fan speed (via pwm) gets its current from an unregulated source. // If all hotends and bed temperature and temperature setpoint are < 54C then the BLUE led is on. // Increase the FAN pwm frequency. I sent M106 code from Repetier but nothing happened. No difference. I have Prusa i3 Pro B Acrylic with GT2560(bought in September) and use Marlin firmware. The fan works if it's connected to fan 1-3 slots, so the fan is working. I have checked all these options. Pin16 is used for LCD panel. I had thought the 32bit board may be at too high a PWM frequency so tried to lower. // Otherwise the RED led is on. Try a lower PWM frequency. Figure 7. I'm running a SKR mini E3 v1.2 with Marlin 2.0.3 Is this fixable by increasing the PWM frequency in Marlin? There is 1C hysteresis. (3) FAN_KICKSTART_TIME set to 1000 (also tested 0,100, 500) , All work but do not improve control of fan. If the fan is mechanically good and there is still noise, then it is the PWM frequency emitted by the fan. Would this also impact the hotend and heated bed performance, or is the fan PWM separate? Unfortunately, hardly anything has changed in the result. Although these fans are relatively new to the market, they are rapidly becoming more popular. 12v fan with a buck converter and ground to the fan. Figure 7 depicts the circuit used for high-frequency PWM. In Marlin, it will be a setting ... You may need to experiment a bit. The Marlin firmware offers several options to reduce noise by software. That's why I developed this hardware solution. I assume it has to do with math and frequency. The external control circuit is simpler with high-frequency PWM, but it can only be used with 4-wire fans. #2 dc42, May 10, 2018. gonzalo Well-Known Member. The issue is the way pwm works. Removes the PWM noise but increases heating in the FET/Arduino //#define FAST_PWM_FAN // Temperature status LEDs that display the hotend and bet temperature. Circuit for driving a fan with high-frequency PWM. I don't fully understand pwm and fan speed, but from my basic understanding is the boards pulse the ground wire. The Ultimaker board uses pin 7 to control the fan speed, but this pin has not a 12v maximum tension, instead it gets it power … - //#define FAN_SOFT_PWM and #define SOFT_PWM_SCALE 0 - are the lines to look for. // Increase the FAN pwm frequency. 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