Fan support?

Would it be possible to use one of the unused ATmega pins on Gen 7 running Teacup firmware as a fan controller pin?

indeed! You can't power the fan directly from that pin but with a circuite similar to the heater controll there is no problem doing that.

Could the pin power a small relay?
Or does it control, not power? Like control a MOSFET?

I am assuming your fan is a 12V DC type.

Even a small relay I would want to control via a transistor. This is quite simple if you don't mind the clicking and don't want PWM.

Using a MOSFET instead of a transistor is almost as simple and is generally better. The trick is to find a "logic level" MOSFET that is commonly available and has a low enough resistance at 5V. My stock favourite is currently IRLB8743, which is overkill for a fan but will work.

A google search for "avr relay control" or "avr mosfet control" provides plenty of examples.

Thank you both. Very helpful.

The SevenSwitch [reprap.org] is a small board implementing the above. Maybe overkill already, but I think having this flowback diode is essential when running coil-based devices, i.e. an DC motor.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

bobc Wrote:
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The trick is to
> find a "logic level" MOSFET that is commonly
> available and has a low enough resistance at 5V.
> My stock favourite is currently IRLB8743, which is
> overkill for a fan but will work.

I can't find one of those near me or on the internet in Australia. Would this work? [www.jaycar.com.au]

That looks almost ideal, I would add a flyback diode as Traumflug suggested. For a small fan you might get away with it, but MOSFETs can be quite sensitive to the "wrong" voltage.

Maybe also try RS [australia.rs-online.com]