4095 Step Grayscale

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rwensley
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4095 Step Grayscale

Postby rwensley » Mon Nov 09, 2015 4:08 pm

Greetings,

I have developed and presently testing, a DAC interface with 4095 step. (Actually 4096 when counting 0).
I am setting the Max 3rd Axis Depth to -0.4095, the steps per mm, set in grbl, is 10000.

Seems to be working well however; as I said I am presently testing this out. Is this of interest to PicEngrave or others on this forum?

Ron Wensley

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Re: 4095 Step Grayscale

Postby Picengravertoo » Mon Nov 09, 2015 6:53 pm

Hi Ron,

Is that depth setting in Inches or mm?

Jeff

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Re: 4095 Step Grayscale

Postby rwensley » Mon Nov 09, 2015 8:22 pm

Hi Jeff,

I am using mm.

Ron

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Re: 4095 Step Grayscale

Postby Picengravertoo » Tue Nov 10, 2015 7:17 am

Hi Ron,

For a metric depth value, should it not be a 3rd Axis Depth of -.6477 which is equivalent to -.0255 in inches for 8bit? (256 .0001" inc. steps when counting 0)

Jeff

rwensley
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Re: 4095 Step Grayscale

Postby rwensley » Tue Nov 10, 2015 8:23 am

Hi, Jeff,

Hmmm... That is interesting. I will need to noodle on that for a while. If there are 10000 steps in one mm then would not 0.4095 mm be 4095 steps? Likewise if there are 10000 steps per inch would not 0.4095' take 4095 steps? Either way 1 step equals 1 bit on the DAC.
I must be missing something in the way grbl utilizes mm and inches. More research is needed.

Ron

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Re: 4095 Step Grayscale

Postby Picengravertoo » Tue Nov 10, 2015 8:59 am

Hi Ron,

When we use a 8bit digital potentiometer for a DAC that takes the step & direction signals from an axis, it requires 393.7 a steps/mm for that axis in grbl for the -0.0255 3rd axis depth which is equivalent to 10,000 steps per inch. If you are setting the axis to 10000 steps/mm in grbl, it will run very slow or maybe not at all trying to process that many steps.

Your stating you accomplished 12bit resolution with your DAC, so unless your using another method then the step & direction signals, even Mach3 can not handle processing 10000 steps/mm for an axis.

Jeff

rwensley
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Re: 4095 Step Grayscale

Postby rwensley » Tue Nov 10, 2015 9:12 am

Jeff,

Perhaps that is explaining my locking up of the system on the other thread. I am using direction and step to drive the 12 bit DAC and as I said I am still testing. Maybe the testing is over with this revelation. If I infer correctly it is not the actual number of steps, 4095 in this case, that is the issue. Rather it is the fact the grbl can not process the steps ate a rate equivalent to 10000 steps per unit. When it tries to do so it gets 'tongue tied' so to speak and losses control. Interesting. More experimenting/research required.

Ron

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Re: 4095 Step Grayscale

Postby Picengravertoo » Tue Nov 10, 2015 10:22 am

I was told on the Shapeoko forum that my 10bit MA3 analog shaft encoder method was so Rube Goldbergish by a moderator there compared to using an electronics means to control the lasers intensity. By us using a timing belt configuration & ratio change from the stepper to the encoder, we are able to keep the steps per low enough and still have the 10bit resolution with the 0-5v analog out to the Flexmod P3 laser driver.

We tested a 10bit DAC from J-Tech Photonics with Mach3 and it required 40000 steps per inch and it would lose position/steps because of the very high and fast stepping it had to process even when setting Mach3 to a high Kernel Speed. The 10bit MA3 shaft encoder works very good with Mach3 too. US Digital does offer a 10bit & 12bit PWM version also.

http://www.usdigital.com/products/encod ... /shaft/ma3

Jeff

rwensley
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Re: 4095 Step Grayscale

Postby rwensley » Tue Nov 10, 2015 10:31 am

Jeff,

I see the advantage of the encoder. I may well end up there at some point. Using the DAC does have challenges.

I found a reference that grbl can handle a stepping frequency of 30kHz reliably. 38kHz seems to be the fringe limit.

So looking at the numbers if I set this
Z max depth = 1 mm
Z step/mm 4095
Z Max feed rate = 439.5604 mm/min = 7.326 mm/sec
The step frequency = 30kHz
So travel time full scale should be 55.9 mS

Ron

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Re: 4095 Step Grayscale

Postby Picengravertoo » Tue Nov 10, 2015 12:20 pm

Ron,

Mach3 can be set up to 100khz Kernel Speed and is a PP CNC controller. The Min is 25khz.

Jeff


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