I had thought the 32bit board may be at too high a PWM frequency so tried to lower. Unfortunately, hardly anything has changed in the result. I'm running a SKR mini E3 v1.2 with Marlin 2.0.3 THE PROBLEM: on my board the pin dedicated to regulate the fan speed (via pwm) gets its current from an unregulated source. I'm trying to add a cooling fan on PWM but it doesn't work. // Increase the FAN pwm frequency. 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. The fan works if it's connected to fan 1-3 slots, so the fan is working. In Marlin, it will be a setting ... You may need to experiment a bit. // Otherwise the RED led is on. The following requirements are measured at the PWM (control) pin of the fan cable connector see Figure 7 and Table 1: PWM Frequency: Target frequency 25 kHz, acceptable operational range 21 kHz to 28 kHz Maximum voltage for logic low: VIL = 0.8 V Absolute maximum current sourced: Imax = … Would this also impact the hotend and heated bed performance, or is the fan PWM separate? #2 dc42, May 10, 2018. gonzalo Well-Known Member. The issue is the way pwm works. Also, If i turn up the fan speed on the ramps when running a print, nothing. 12v fan with a buck converter and ground to the fan. I sent M106 code from Repetier but nothing happened. Although these fans are relatively new to the market, they are rapidly becoming more popular. Pin 7 is set to PWM and it's not working. // Increase the FAN pwm frequency. Try a lower PWM frequency. I have checked all these options. Is this fixable by increasing the PWM frequency in Marlin? The PWM period is now \$ 0.1\tau=1ms\$ and duty cycle is still 50%. (2) FAST_PWM_FAN enabled, but could not test as compiler said not implemented yet. The following is my code for the fan that is at the bottom of your config.h . As you can see, the speed of the motor swings widely because the frequency of the PWM is not high enough. They only make this noise when not running on 100% fan speed. Circuit for driving a fan with high-frequency PWM. 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 … No difference. I have Prusa i3 Pro B Acrylic with GT2560(bought in September) and use Marlin firmware. 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. 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. - //#define FAN_SOFT_PWM and #define SOFT_PWM_SCALE 0 - are the lines to look for. I assume it has to do with math and frequency. If the fan is mechanically good and there is still noise, then it is the PWM frequency emitted by the fan. The external control circuit is simpler with high-frequency PWM, but it can only be used with 4-wire fans. Figure 7 depicts the circuit used for high-frequency PWM. Figure 7. // If all hotends and bed temperature and temperature setpoint are < 54C then the BLUE led is on. So in theory we could run. That's why I developed this hardware solution. 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. 50% 24v pwm is not the same as 50% 12v pwm. The Marlin firmware offers several options to reduce noise by software. 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