Generation 2 OnABoard

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RepRap Gen 2 OnABoard

Release status: Experimental

Gen2Backplane-v0.1.GL.png
Description
One board to handle most of the gen 2 electronics.
License
unknown
Author
[[User:{{{author}}}]]
Contributors
Based-on
[[]]
Categories
CAD Models
External Link


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.

Circuit Board

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The lower right is an Arduino mini board. I plan to change this to the same chip that is used in a Sanguino, in a DIP socket.

Across the middle I have 4 pololu stepper drivers. available here. This board supports up to 2 A per coil (with proper cooling) and micro-stepping in full, 1/2, 1/4, 1/8 or 1/16 steps. Under each stepper driver there are jumpers used to configure the micro-stepping.

Below that is two PWM drivers for the fan and heater. I hope to add two more to support a heated build platform and a future expansion.

Below that 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 2.7K load resistor on the 5V line, which is to help the regulator in the power supply. There will be a PTC resettable fuse 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 temp sensor has a place for a resistor between +5V and the sensor pin, meaning that a separate thermistor board is not needed.

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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.

Pin Assignments

usage Arduino ATMega644P Special Function
X_STEP D15 PD7 PWM
X_DIR D18 PC2 TCK
X_MIN D20 PC4 TDO
X_MAX D21 PC5 TD1
X_ENABLE
Y_STEP D23 PC7
Y_DIR D22 PC6
Y_MIN D25 (A6) PA6
Y_MAX D26 (A5) PA5
Y_ENABLE
Z_STEP D29 (A2) PA2
Z_DIR D30 (A1) PA1
Z_MIN D2 PB2 INT2
Z_MAX D1 PB1 INT1
Z_ENABLE D19 PC3 TMS
E_STEP D28 (A3) PA3
E_DIR D16 PC0 SCL
E_ENABLE
HEATER1 D14 PD6 PWM
TEMP1 A4 (D27) PA4
HEATER2 D4 PB4 PWM
TEMP2 A7 (D24) PA7
FAN D3 PB3 PWM
PS_ON D17 PC1 SDA
ENCODER D0 PB0 INT0
AUX A0 (D31) PA0
MOSI D5 PB5 MOSI
MISO D6 PB6 MISO
SCK D7 PB7 SCK
RX (Serial) D8 PD2 RX0
TX (Serial) D9 PD3 TX0
RS485 IN D10 PD2 RX1
RS485 OUT D11 PD3 RX2
RS485 Tx Enable D12 PD4 PWM
RS485 Rx Enable D13 PD5 PWM