Generation 2 OnABoard
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Release status: Experimental
Description | One board to handle most of the gen 2 electronics.
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License | unknown
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Author | [[User:{{{author}}}]]
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Contributors | |
Based-on | [[]]
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Categories | |
CAD Models | |
External Link |
Contents
Generation 2 OnABoard
This is a single board that contains most of the electronics required to run a RepRap. All the components that require soldering are through-hole. The cost is slightly less than the generation 2 electronics because there is less need for connectors and PCB space to support connectors.
The board uses the ATMega644P. It can be treated as a Sanguino based Gen 2 electronics and will work with existing firmware that supports the Sanguino.
Schematic
Project Files
File:Gen2OnABoard.tar.gz The project archive contains the gEDA and PCB files as well as the Gerber exports required for printing.
Circuit Board
The lower right is an ATMega644P, in a DIP socket. This is the same chip that the Sanguino and the Gen3 motherboard uses. It should be easy to get existing firmware to work with this board.
Near the top I have 4 pololu stepper drivers. See Pololu_Electronics for more information on these boards. Under each stepper driver there are jumpers used to configure the micro-stepping.
On the left side there are three PWM drivers for the fan and two heaters.
On the right, below the stepper drivers is a 24-pin ATX connector. I'm using the 5V standby to power the microcontroller and I have a pin on the Arduino connected to the power switch wire so that the Arduino will be able to turn the power supply on and off. There is also a 30 Ohm load resistor on the 5V line, which is to help the regulator in the power supply.
Between the power connector and the microprocessor there are PTC resettable fuses on each of the 5V and 5V standby lines. These will prevent traces from burning up in the event that something gets connected incorrectly. The 12V and GND lines are not protected in this mannor.
The two temp sensors and the AUX sensor have places for a resistor between +5V and the sensor pin. They also have places for a capacitor between GND and the sensor pin. By populating these components it is possible to connect a thermistor directly without using a thermistor board.
I made all the traces that carry significant current thicker. Most of these are 0.05 inch.
Most of the traces on the top half of the board are on the bottom layer with a ground plane filling the top layer. I hope this will help to cool the stepper drivers, but I am uncertain if I can efficiently transfer heat through the pins from the breakout board.
Since there isn't much going on under the stepper drivers I filled the bottom layer in that area with a +12V power plane. The idea here is to limit interference between the stepper drivers each pulling from the same supply.
I'm estimating this will cost about $100 for the prototype board.
To build a RepRap using this board you will also need a USB-ttl cable, 3 or 6 opto-endstop and an ATX power supply.
Part List
https://spreadsheets.google.com/ccc?key=0Ajao6Zxy4uHGdEJheVBZOVRqSXJkSlNiVDFaTFNvYUE&hl=en
Pin Assignments
usage | Arduino | ATMega644P | Special Function |
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X_STEP | D15 | PD7 | PWM |
X_DIR | D18 | PC2 | TCK |
X_MIN | D20 | PC4 | TDO |
X_MAX | D21 | PC5 | TD1 |
X_ENABLE | GND | ||
Y_STEP | D23 | PC7 | |
Y_DIR | D22 | PC6 | |
Y_MIN | D25 (A6) | PA6 | ADC |
Y_MAX | D26 (A5) | PA5 | ADC |
Y_ENABLE | GND | ||
Z_STEP | D29 (A2) | PA2 | ADC |
Z_DIR | D30 (A1) | PA1 | ADC |
Z_MIN | D2 | PB2 | INT2 |
Z_MAX | D1 | PB1 | INT1 |
Z_ENABLE | D19 | PC3 | TMS |
E_STEP | D28 (A3) | PA3 | ADC |
E_DIR | D16 | PC0 | SCL |
E_ENABLE | GND | ||
HEATER1 | D14 | PD6 | PWM |
TEMP1 | A4 (D27) | PA4 | ADC |
HEATER2 | D4 | PB4 | PWM |
TEMP2 | A7 (D24) | PA7 | ADC |
FAN | D3 | PB3 | PWM |
PS_ON | D17 | PC1 | SDA |
ENCODER | D0 | PB0 | INT0 |
AUX | A0 (D31) | PA0 | ADC |
MOSI | D5 | PB5 | MOSI |
MISO | D6 | PB6 | MISO |
SCK | D7 | PB7 | SCK |
RX (Serial) | D8 | PD0 | RX0 |
TX (Serial) | D9 | PD1 | TX0 |
RS485 IN | D10 | PD2 | RX1 |
RS485 OUT | D11 | PD3 | TX1 |
RS485 Tx Enable | D12 | PD4 | PWM |
RS485 Rx Enable | D13 | PD5 | PWM |