using the unused arduino pins

I notice on the RAMPS board that a large number of arduino pins are not being used. I even have an LCD on my printer and there still is a large number of pins seemingly available.

I know I would be subject to current limitations, but am I right in assuming that I can use these pins for my own purposes? It would be great if this were so because, for marlin at least, I can control these pins via code and, therefore, very easily from my host software. I believe there are even some PWM pins available which would make it relatively simple, with a small transistor circuit, to control the speed of a couple more fans.

Sure. With Teacup firmware you can configure an unlimited number of devices, see the DEFINE_HEATER section in config.h. And no, _HEATER_ doesn't mean the device has to actually heat something, it can also be a fan or a lamp or a refrigerator Works for PWM and non-PWM, the corresponding G-code is M104.

In Sprinter and Marlin, you have M42 to turn arbitrary pins on and off.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

im beginning to understand how these things work ...


but i got lost when i hear you guys say M104, M42 ... what are these?

These are g code commands. G code normally consists of the movement and extruding commands that your slicer produces, but there are many other commands available (and not all of them start with G) that let you do things like turn arduino pins on and off, set firmware parameters, etc. Most host software provides some mechanism where you can enter g code interactively to directly control you printer.

A description of most (all?) available G-codes is here: [reprap.org]

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

k im just intrigue by this part ... how does 1 use this? if i guess ... there is 1 pin thats a trigger ...

G29-G32: Bed probing
G29 Detailed Z-Probe
probes the bed at 3 points.
G30 Single Z Probe
probes bed at current XY location.
G31 Report Current Probe status
reports whether Z probe is triggered.
G32 Probe Z and calibrate with FPU
probes the bed at 3 points and updates transformation matrix for bed leveling compensation.