Why don't use Arduino Mini or Rasberry Pi instead of Mega

[irresistiblecam]

Why don't use the Arduino Pro Mini instead of Arduino Mega.
It is much cheaper! The best would be use the 3,3V version so I could connect the inexpensive Nokia LCD display.

If the microprocessor of Arduino Pro Mini is too slow, why don't use a Rasberry Pi, the price is almost the same of Mega,
and you already have microsd reader and LAN., And also you could use LinuxCNC and a PC Monitor.

Instead of A4988 why don't use the DRV8825, that for almost the same price, manage more current?

[Turnkey]

I suspect it's due to all the firmware (Marlin) that has been written in C to run on Arduino which probably wouldn't be compatible with RasPi without extensive rewriting. Granted the Mega is a little slow, I wish I was able to raster faster but it does the job for me as a hobbyist laser cutter/engraver.

Marlin was originally written for 3D printers, and those didn't need much computer processing power to run.

[irresistiblecam]

If Arduino Mega is slow then the arduino pro mini is not to keep in consideration.

I am newbe, but I think that if you use Raspberry you don't need Marlin firmware, just because already a good
opensource software that read g-code.
The only thing to do is to configure it, for raspberry and for k40 laser, so you can manage the power of the k40 laser with gcode, maybe different in the same file.

http://funofdiy.blogspot.it/2013/10/a-raspberry-pi-controlled-mini-laser.html

look the speed of engraving, what do you thing, is it faster than Mega?
http://www.yoursse.com/watch?v=WEVeHWpXeF4

[Turnkey]

Looks like the same speed as we can do on the mega.

[John Dickinson]

You can't use the Raspi with the normal OS because the kernel will not support real time and that is needed for accurate stepper motor control. If you want to do it with a Raspi then all of the OS will need to be written with that in mind as it is with Marlin for the Arduino. It is also much more expensive. You can buy the Marlin compatible board with driver board, stepper drivers and LCD for around £20, the Raspi alone is more than that.

[John Dickinson]

The 2560 will go faster than the K40 can handle, a lot faster. You run out of laser power and mechanical ability long before you reach maximum speed on the Arduino.

[irresistiblecam]

Good. So i declined the idea about Raspberry/odroid

What about to use Arduino Pro Mini instead of Arduino Mega?

What is the speed difference?

With arduino Pro mini, do you  run out of laser power and mechanical ability long before you reach maximum speed on the Arduino Pro mini?

[Turnkey]

I find with the mega I can run rasters at around 4500 mm per minute feed rate reliably, and up to 5500 mm per minute where it develops some strange artifacts at the left and right sides of the burn where the laser head is decelerating. Though that last issue may be code related.

What I have found though is there is a limit in the current setup in how much data I can send the system for rastering and have it burn it without running out of buffered data or similar. Not really a big issue since 4500 is still pretty damn fast for most things and we're talking about a machine that costs sub $600 all up to build.

For vector cuts the above isn't an issue at all, it's just rastering that could be optimised in the future.

[irresistiblecam]

Thank you for your infos.

But what about my question?

[John Dickinson]

If no one here has ever used one then you are going to have to get paper, pencil and calculator and then you can work out how fast it can cope with.

[Chad Davis]

GRBL was created for an Uno and took a good bit of engineering to pull off. A pro mini has half the flash and half the SRAM of the Uno. Doubt someone will take on that even greater challenge to save just a few dollars and a few square inches.