On my list of upgrades to my Prusa i3 I have dual extruders (which is being worked on currently), and auto bed leveling (next on the list).

I'm seeing something that hopefully isn't contradictory.

For dual extruders, I've changed motherboard type to 34 - which disables the fan control in lieu of power for a second hot end. The fan extender then controls dual fans via D4/D5, with 12v power coming from the 12v lead next to the X axis stepper driver.

To enable power to the servos section of the ramps, it appears that D12 and VCC need to be jumpered (PS-ON and VCC to the left of the reset button on the Ramps board).

My concern is that A: I'm feeding power to the fan extender via the 12v lead, and B: I'm "enabling power" to the servo's via jumpering D12.

Would I only need to do one of these to accomplish my goal of supplying power for fans and the bed leveling servo or am I OK with both of these?

Thanks in advance.

I got this working by connecting the servo to one of the unused pins (D40) and modifying the firmware.

Here is the G+ post with some details:
[plus.google.com]
Here is the commit with the changes I made to marlin:
[github.com]

I basically connected the fan extender to the normal place (and did not jumper the 5V header next to it, just connected 12V to the extra board according to the docs).
I then modified marlin to define a new motherboard type, which basically just looks like nr 34, but additionally places the normal fan on pin 6 and servo on D40.
Additionally I also run the e3d hotend fan on the other fan extender output (d11) with the extruder auto-fan functionality in marlin, so it automically turns on/off above/under 35C on the hotend. That way I don't have the e3d fan running all the time.

Hi

Excellent post, now i updating my prusa i3 with two extruders and the servo autoleveling,i have the same problem and i wanna try this solution but i have a question, from where do you take the gnd and 5v for the servo?.

Thanks