Hardware advice

Electronics related to CNC

Hardware advice

Postby Yaro » Wed Jul 16, 2014 7:46 am

Hi, i see a lot of people using differents control boards and programs.
I see all use Mach3, why? i see it also doesn't support usb. Other people use grbl, others use reprap.
Can someone advice me which is better or advantages/disadvantages they have?

Thank you.
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Re: Hardware advice

Postby Techgraphix » Thu Jul 17, 2014 2:55 pm

First: for what kind of machine you want a controller? As you posted it in Home Built CNC Lasers, i suspect you want to control a laser with it?
For a laser are, in fact, only a few controllers fully suitable: lightobject's AWC608, Thunderlaser's DF212, Leetro's MPC6515 to mention a few.
These are dedicated lasercontrollers with engraving possibilities.
Other more CNC-Mill/Lathe oriented soft-and hardware can control a laser but engraving is a problem.
Why Mach3 is widely used over expensive controllerboards... well, because Mach3 is not too expensive, even if you pay for the license.. (the demo is free and does already work for a few people)
Moving the X, Y and Z-axis is not the problem. turn on and of the laser and control the power is something else..

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Re: Hardware advice

Postby Yaro » Fri Jul 18, 2014 7:58 am

So mach3 just a programmable controller like arduino or raspberry but provided with program. But what is the real problem to control engraving? Powersupply haven't already a potenziometer and on/off pins?
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Re: Hardware advice

Postby cvoinescu » Fri Jul 18, 2014 8:52 am

Yaro wrote:But what is the real problem to control engraving? Powersupply haven't already a potenziometer and on/off pins?

This is no 100 mW laser diode we're talking about, it's a 40 W carbon dioxide laser. You have lots of power, so you have to move very quickly to just engrave, and not cut, the material. Sure, you could reduce power a lot and go much slower, but that's a waste of capability, and there's only so much you can reduce it and still have good control. Because you move very quickly, the laser power needs to be modulated, whether analog or PWM, very very quickly; if PWM, the timing has to be accurate too. This is beyond the capabilities of most microcontrollers. With PCs, there are interrupts and other things going on that cause jitter. The best tool for the job is a digital signal processor (DSP), which is what's on those dedicated laser controllers.
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Re: Hardware advice

Postby Yaro » Fri Jul 18, 2014 11:14 am

It's a bit expensive a chinese DSP, i see price starting from 300 dollars. Really no one haven't ever built a DSP with an opensource microcontroller? Otherwise, if you set manually low power and just pulse laser without modulating it, isn't possiblity to dot engrave?(something like a normal printer)
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Re: Hardware advice

Postby cvoinescu » Fri Jul 18, 2014 11:40 am

Yes, it is possible, and people do it, but it's slow, and you can't do grayscale unless you slow down even more. If you want to do 200 DPI grayscale (256 levels) using PWM, you need 1,024,000 clock cycles per square inch -- so if you have an 8" x 8" design to engrave, it takes under a minute if your PWM clock is 2 MHz, but something like an hour if you bit-bang it in software on a 16 MHz CPU.
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Re: Hardware advice

Postby Yaro » Fri Jul 18, 2014 12:56 pm

Ok, thank you. So if you want more speed you will need more expensive cpu. Do you have any project of someone which have tryed homemade pwm and bit-bang for better understanding? I've tryed to google but i didn't find anything.
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Re: Hardware advice

Postby Techgraphix » Fri Jul 18, 2014 5:19 pm

Yaro wrote: I've tryed to google but i didn't find anything.

Because everybody who's building a good laser knows that it will cost several thousands of dollars.. A good controller is a part of that.. you will only find them second hand in very rare occasions. why? beacause once someone bought such a controller, he won't degrade to mach3 anymore.. only upgrade, for instance: from moshi to lightobject... but nobody want to have a moshi, especially nog second hand..

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Re: Hardware advice

Postby sofiabovinoclaudia » Tue Aug 15, 2017 12:54 pm

Do you have any project of someone which have tryed homemade pwm and bit-bang for better understanding? You can read about this crazy bulk review
Last edited by sofiabovinoclaudia on Tue Aug 22, 2017 10:54 am, edited 1 time in total.
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Re: Hardware advice

Postby terjeio » Sun Aug 20, 2017 6:56 am

I have made my own controller, it has a 32-bit ARM MCU as its core processor. I do not use PWM, I have an on-board DAC for controlling the power level. There (IMO) has to be a low-pass filter on the PWM (or rather power level) input the of laser PSU, this will restrict how fast the power may be changed. My controller supports 3 different modes, native bit map engraving with up to 128 gray-levels (bit-banging?), Grbl-mode with additional M-code support for PPI settings etc. and Mach3 mode via a piggyback BOB. I have been considering publishing my design and code on github but have not yet done so as I believe it may be of limited interest...
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