Higher fidelity on PWM on DUEX5

[injoi9000]

I am using the PWM ports on the DUEX5 to control a fan with a speed controller. It appears I only have a resolution of S4... as in there is no change in speed between S70 until S74. Is there a way to get higher fidelity using the PWM M280 commands?

[dc42]

The resolution should be 8 bits, because the SX1509B chip on the DueX provides 8 bit intensity control on the PWM output. Have you measured the output pulse timing using an oscilloscope?

[injoi9000]

@dc42 I don't really understand...Does the 8 bit resolution map to a single "S1" digit?

Unfortunately, I don't have an oscilloscope, is there any other way to debug this?

[dc42]

I am sorry, I misread your post. I now see that you are using the PWM ports, not the fan ports.

Please see this post https://forum.duet3d.com/topic/8453/microsecond-resolution-when-using-m280-for-servo-control. In summary, the following should improve the resolution:

• Use firmware 2.03RC2 instead of firmware 2.02
• Or use a PWM port controlled by a timer channel instead of a PWM channel