using all 4 servo pins
July 21, 2015 10:21AM
I have a duel head water cooled machine that I designed and built myself. While the machine is working great I seam to be running out of features on the Ramps boards. I was hoping to use all 4 Servo pins to drive fans. I purcahsed an RRD board to attach to the servo's pins but I see it only has circuity to control fans on pins D6 and D11. How do I control Fans on D4 and D5? Do I need to get a second RRD board and modify them to work on the other 2 pins or is there a RRD board out there that allows all 4 pins. I'd like to attach a cooling fan to each extruder (2) a cooling fan on the Radiator of the liquid cooling system, and then have LED lights attached to the 4th one.
Re: using all 4 servo pins
July 21, 2015 12:50PM
The RRD expansion board is a bad design if you want to use all 4 ports. Build your own extender or there are ready-made alternatives.

Edited 1 time(s). Last edit at 07/21/2015 12:51PM by cdru.
Re: using all 4 servo pins
July 21, 2015 02:55PM
Yeah someone needs to make a 4 output RRD board! I'm amazed one doesn't exist already! There is no reason for me to make single channel boards when I can make a 4 channel one. I'll probably whip one up and send it to OSH park.
Re: using all 4 servo pins
July 21, 2015 05:41PM
Does anyone have the schematic for the RRD fan extender board? I can't seam to find the EAGLE Files anywhere.
Re: using all 4 servo pins
July 24, 2015 02:27PM
Just look at the pictures here - []

If you're able to send off a design to OSH Park you're capable of looking at the photo and recreating the traces. It's not a very complicated circuit board. The only thing you might not be able to make out is the MOSFET and that's a IRF8313PBF.
Re: using all 4 servo pins
July 25, 2015 12:28PM
No office cdru but yes I am fully capable of designing my own. I wanted to see what they had created and the eagle files for the RRD would have had board dimension and pin locations already there saving times. Degrading comments and shark attitudes are what drive people away from on line forums. This is suppose to be an open source community sharing ideas and designs not telling people to go do it yourself and not ask for what is already done. While I thank you for your input I thing consideration of what is written should always be examined before posting on line.
Re: using all 4 servo pins
July 28, 2015 09:56AM
Slow down there turbo. I wasn't trying to office [sic] you. I was just trying to point out that it's a simple design and that if you're capable enough to send something off to OSH Park to be produced, just recreating the design won't be a problem and probably be faster. It's a really simple circuit. (Here's the schematic btw: [] I doubt you'll find actual Eagle files) Board dimensions won't be that much help if you're trying to double the amount of usable outputs as the board real estate is already almost completely utilized. Similarly, the output pins position doesn't matter much since you're doubling those as well. The input pins are just standard .1 spaced female headers in a 3x4 grid.

But feel free to jump all over me for pointing out that just recreating it probably would take less time than posting for the files that likely don't publicly exist.
Re: using all 4 servo pins
July 17, 2016 10:50PM
I figured out something that I think is worth sharing. As stealthtransam said, the RRD fan extender only uses pins 6 and 11. The current Marlin actually uses 4 and 5 as the default with the fan extender physically shifted up two pins to align with those two pins. This means the two servos (6 and 11) are still available.

To use 4 fans we should be able to just use a second fan extender board with the configuration above. Just use jumper pins to connect the second extender with the first shifted up. I'll try that now because I have an extra, but I'm thinking of using these to add the third/fourth (and maybe the first/second later since it can handle a little higher current [0.5-1.0+A] and I need ~700 mA):

I was considering this one, but it seems like it has to have a signal voltage of >9V and arduino uses 5 if I understand correctly since it's outputting for a servo:

And I also found a way to make my own (but the individual modules cost less than the parts):
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