Wiring for Load Amplifier to drive extruder

Controllers Smoothie
1

Hi all,

I am working on a printer with a new type of extruder that doesn’t feed material as a linear string but instead
pushes on a spray can, and to have accurate pressure, I am going to use a load cell with its amplifier [1].
I am using a Smoothieboard and will eventually have to add additional modules to the firmware to

  1. read pressure information
  2. adapt extruder position based on the pressure and timing (instead of using simple stepper motor distance)

What pins do you suggest I use for that? I read that I should use GPIO pins, but which ones are these?
There seems to be many (more than 13) free pins around the board, so I am confused as to
which pins are the free GPIO pins.

Thanks for any clarifications and/or hints.

[1] SparkFun Load Cell Amplifier - HX711 (as new user, I cannot post links yet, it’s on sparkfun’s website, product 13230)

Imported from wikidot

2

Hey

This sounds extremely difficult to implement.

Sounds like your sensor board uses TWI for communication, you should read the LPC1769’s datasheet to find how to interface with that.

About free gpio pins, it depends exactly on what you are using on the board, see http://smoothieware.org/lpc1769-pin-usage

Cheers.

3

Thank you for the link.
Would it make more sense to use an Arduino since it’s trivial to communicate with the sensor board with Arduino? Is there an easy way to interface the smoothieboard with an Arduino and use the Arduino as a slave from the Smoothieboard side?
Since the sensor reading will be tightly coupled with the extruder, I guess I either take care of both on the Arduino side, or of both on the Smoothie side. Of course, I’d rather not have to interface with an extra board…

I looked at the LPC1769 datasheet and the pin pairs for I2C (TWI) correspond to the ones in the pin usage list:

  • (p0.0, p0.1) : in smoothieboard, listed as “Internal I2C bus. Used for digipots and port expander.”
  • (p0.10, p0.11) : assigned to beta_en_pin and beta_dir_pin
  • (p0.19, p0.20) : assigned to gamma_en_pin and gamma_dir_pin
  • (p0.27, p0.28) : User i2c port. sd cd on rrd glcd adapter

I am using M1 for X, M2 for Y, M3 for Z and M4 for E. I have the ethernet cable used and the sd card of course.
So it looks like the only available pair is (p0.27, p0.28) (unless I can also use (p0.0, p0.1), but since it reads “internal”, I guess not)
What does User i2c port. sd cd on rrd glcd adapter mean?
Does sd mean it is used for the sd card?

I am not using any display (glcd), so hopefully that pair is free.

4

I am not using any display (glcd), so hopefully that pair is free.

Yep it is.

Would it make more sense to use an Arduino since it’s trivial to communicate with the sensor board with Arduino? Is there an easy way to interface the smoothieboard with an Arduino and use the Arduino as a slave from the Smoothieboard side?

You can communicate any way you want really, it’s all going to depend on how much work exactly you want the arduino to do.