RepRap for Science—How to Use, Design, and Troubleshoot the Self-Replicating 3-D Printer - Open-Source Lab: How to Build Your Own Hardware and Reduce Research Costs - page 154

of 0.2 Ω, ultimately the math you need to know to set the right Vref is 0.28× (max current (A)
of your motor). If you purchased the motors recommended in the BOM, it is 0.28 × 1.7 = 0.476.
If you are really curious about the math behind this tuning, the Reprap wiki provides a very
good overview. 15
Turn the trim pot clockwise to turn down the voltage, clockwise to turn it up. Be aware there
is no stopper on the trim pots . It is possible to over turn the trim pots, so please use a multimeter
when adjusting. Read the voltage and adjust until proper Vref is set. You can also overshoot
by a litle bit (roughly within 0.1 V). Finally, plug in the power supply into the Melzi board
and you are ready to start—black is ground.
5.3 Software
The software tool chain consists of three discreet parts: firmware, printer interface and slicing
software (although some interfaces can also provide slicing). In short, the slicing software
takes a 3-D model and converts it to g-code, which is a numerically controlled programming
language that tells the 3-D printer how to make your model. The printer interface sends the
g-code to the printer and the firmware interprets the g-code into movements.
5.3.1 Firmware
Firmware is really a software that resides on the printer controller board (in this case the Melzi).
The firmware (1) interprets g-code into motion, controlling the motors, the temperature of the
hot end and heated build platform, (2) takes notice when limit switches are activated and (3)
echos responses when commands are executed or a problem occurs. Ideally, you will only
need to configure your firmware and upload onto the controller board once and the printer is
then ready for use. If you are using a 3-D printer that is known to be functional already, then
it is unnecessary to complete the following steps pertaining to firmware configuration and up-
loading. Practically, firmware will be occasionally upgraded, so the practice of configuration
and uploading is worth understanding.
5.3.2 Printer interface
The printer interface is software that runs on the host computer atached to the printer via a
USB cable. It provides an interface for controlling the printer: seting temperatures, moving
axes, starting print jobs, etc. The printer interface essentially converts interactions with it into
g-code—when a buton or linked image is clicked or text is entered into the printer interface,
it is converted into g-code that is then sent to the printer firmware for interpretation into some
action.
5.3.3 Slicer
A slicer is software that converts a solid model (typically an STL file type) into the g-code that
the printer firmware can interpret into action. After slicing a model, the g-code is either loaded
onto a micro-SD card, which is then inserted into the printer control board and then activated
through the printer interface or the g-code is loaded into the printer interface and then trans-
mitted to the printer controller board in small chunks over via the USB connection.