I finally went ahead and did it. I forced my DRV8825 drivers into fast decay mode. I've been thinking of doing this for a while. I tried the whole freewheeling diode thing (made things worse).
After looking at many other mods and the Texas Instrument datasheet, this is what I came up with.
Bringing the DECAY pin (pin 19 on the IC) to logic high (5v) sets the driver in fast decay mode. Pin 18 (nFAULT) isn't used in this configuration. It is tied to the SLEEP pin via a resistor (1.5kohm I think). Under normal operation, the FAULT pin isn't held at 5V.
That being said, the M3 pin on the top is right next to the FAULT pin. The M3 pin is at 5v when in 1/32 stepping mode. I tied the M3 and FAULT pins together on the topside.
[attachment 84673 drv8825_top.jpg]
Ignore the brown/orange color - that is from the liquid flux I was using. I'm too lazy to clean it up with some denatured alcohol.
This puts 5v on the FAULT pin, which sends 5v to the nFAULT pin on the IC. I then tied pins 18 & 19 together on the IC.
[attachment 84672 drv8825_underside.jpg]
Success. Drivers are in Fast decay mode. Definitely a different noise. More high pitched and annoying, even though it seems 'quieter' and the motors seem to run smoother. I have not had a chance to really put it through the paces to see how it affects print quality.
After looking at many other mods and the Texas Instrument datasheet, this is what I came up with.
Bringing the DECAY pin (pin 19 on the IC) to logic high (5v) sets the driver in fast decay mode. Pin 18 (nFAULT) isn't used in this configuration. It is tied to the SLEEP pin via a resistor (1.5kohm I think). Under normal operation, the FAULT pin isn't held at 5V.
That being said, the M3 pin on the top is right next to the FAULT pin. The M3 pin is at 5v when in 1/32 stepping mode. I tied the M3 and FAULT pins together on the topside.
[attachment 84673 drv8825_top.jpg]
Ignore the brown/orange color - that is from the liquid flux I was using. I'm too lazy to clean it up with some denatured alcohol.
This puts 5v on the FAULT pin, which sends 5v to the nFAULT pin on the IC. I then tied pins 18 & 19 together on the IC.
[attachment 84672 drv8825_underside.jpg]
Success. Drivers are in Fast decay mode. Definitely a different noise. More high pitched and annoying, even though it seems 'quieter' and the motors seem to run smoother. I have not had a chance to really put it through the paces to see how it affects print quality.