RepRap electronics systems

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This page is outdated, maybe look at List of electronics

Contents

Interfaces

One of the things we've striven for in this project to achieve modularity with our designs. The way this is achieved is through interfaces. You can basically think of the electrical connection between different components as an interface. There are major parts in the systems where it makes sense to have a modular interface. The electronics system is one area where this makes a lot of sense. There are basically two interfaces between the electronics: the computer/reprap interface and the electronics/machine interface. These are generally the same regardless of which system of electronics you are using.

Computer / RepRap interface

The way the RepRap machine talks to your computer is over a standard serial connection. In the generation 1 electronics, this is achieved through the Power/Comms board with either a real serial connection, or a USB->Serial converter cable. Either way works the same. Within the Generation 1 electronics, the boards communicate via a token ring which the host computer is a part of.

In the second generation electronics, it works in much the same way. The Arduino is the entry point for the serial link. A standard arduino uses a USB cable and has the USB->Serial chip onboard. Some Arduino clones such as the Boarduino omit the chip to save costs and require you to use a USB->Serial cable as well. The Arduino then internally emulates the token ring network in order to talk with the host software.

Electro-Mechanical Interface

The RepRap machine itself consists of a variety of electromechanical components. Each of these has the same interface, regardless of the electronics driving them. Both the generation 1 and 2 electronics have been designed to accept and control the same electromechanical components. The major difference between the versions of electronics is the microprocessor controlling them, and the way in which the electronics drive the components. Below, we'll look at the various parts.

Stepper Motors

Stepper motors are the drive system for each axis of a RepRap machine. The connectors are different, but you still hook up steppers to the stepper controller board in each system.

Opto Endstops

The opto endstops are the same in both systems. They both simply plug into the stepper controller boards which then interpret the signals.

DC Motors

A DC motor is used to drive the extruder. You simply hook it up to the proper board.

Heater

A heater is used to heat up the heater barrel in order to extrude plastic. It is simply a wire that current is passed through. It is also simply hooked up to the appropriate board.

Temperature Sensors

The temperature sensing is currently done with a thermistor. Both systems have a circuit board that the thermistor must be wired to in order to sense the temperature. They do however use differing methods for measuring the temperature.

Electronics Versions

As the project grows, we make mistakes and learn lessons. The electronics have gradually evolved over time due to this influx of knowledge. We have tried our best to keep everything compatible, and I believe we've done a good job. Here is the current status of the various electronics setups.

Generation 3: Sanguino Based Electronics

Pros

  • easy programming through Arduino
  • rock solid compiler (avr-gcc)
  • chopper-style stepper driving
  • ADC temperature readings
  • based on other open source projects (Arduino, avr-gcc)
  • modular on network and peripheral level
  • more powerful atmega644p chip
  • rs485 comms network for robust comms
  • multiple, modular tool system
  • simplified connectors / wiring

Cons

  • Software still under development
  • Majority of parts are SMT only


Generation 2: Arduino Based Electronics

Pros

  • easy programming through Arduino
  • rock solid compiler (avr-gcc)
  • chopper-style stepper driving
  • ADC temperature readings
  • based on other open source projects (Arduino, avr-gcc)
  • modular on network and peripheral level
  • more powerful atmega168 chip

Cons

  • More circuit boards to deal with
  • more centralized to one processor (may be pro or con depending on the person)
  • Shortage of I/O pins (though the sanguino addresses this)

Generation 1: PIC Based Electronics

Pros

  • software that currently works
  • relatively large base of users who have them built and are actively using them.
  • modular design at network level

Cons

  • lack of easy programing
  • lack of a reliable compiler (SDCC issues)
  • very rough stepper driving
  • poor temperature measurement, etc.