Re: [Emc-users] OT: analog to step/dir

[Gregg Eshelman]

Like this. Could remove the pot and switches to remote mount or connect to 
something else for control inputs. One switch is on/off, other is direction. 
Pot is speed control.
 http://www.ebay.com/itm/311203030663

On Thursday, April 13, 2017, 11:15:13 AM MDT, Jon Elson 
 wrote:On 04/13/2017 05:39 AM, andy pugh wrote:
> On 13 April 2017 at 01:53, Eric Keller  wrote:
>>    USDigital used to have something called an
>> "EPOT" but they got rid of it for some reason.
> https://tinyurl.com/ke75fzx any good?
>
No, not a digital pot, he wants a device that puts out 
step/direction in response to analog input.
I assume to take analog velocity command from some 
controller and drive a stepper motor.

Jon
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Re: [Emc-users] OT: analog to step/dir

[Chris Albertson]

On Thu, Apr 13, 2017 at 10:10 AM, Jon Elson  wrote:

> ...he wants a device that puts out
> step/direction in response to analog input.
> I assume to take analog velocity command from some
> controller and drive a stepper motor.


This is a job for the smallest/cheapest micro controller.   An Arduino
clone could do this

The software could read an analog pin then program a count/timer to make
pulses.  Then while the chip's hardware pulse generator runs, the software
periodically reads an analog pin and re-programs the timer to go faster or
slower.

Details are things like the range of the analog signal the requires D/A
conversion resolution and how many times per second you need to read the
analog signal.


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Re: [Emc-users] OT: analog to step/dir

[Jon Elson]

On 04/13/2017 05:39 AM, andy pugh wrote:
> On 13 April 2017 at 01:53, Eric Keller  wrote:
>>USDigital used to have something called an
>> "EPOT" but they got rid of it for some reason.
> https://tinyurl.com/ke75fzx any good?
>
No, not a digital pot, he wants a device that puts out 
step/direction in response to analog input.
I assume to take analog velocity command from some 
controller and drive a stepper motor.

Jon

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Re: [Emc-users] OT: analog to step/dir

[Gene Heskett]

On Thursday 13 April 2017 08:47:26 Eric Keller wrote:

> On Thu, Apr 13, 2017 at 8:29 AM, andy pugh  wrote:
> > On 13 April 2017 at 13:07, Eric Keller  wrote:
> > > I have a data acquisition device that only puts out analog
> > > voltages.
> >
> > It sounds like almost any motor would be easier to control in this
> > application than a stepper motor.
>
> Right now, I am trying a servo motor.  A lot of motors would be fine
> if I could allow them to spin, but I can't.  Analog control without
> any feedback is a problem, no doubt.

Andy is correct.  Can this job be done by an RC model servo-motor? they 
are controlled by the pulse width, and are fairly accurate, often better 
than 1 or 2 percent of the output range. Typically half a turn range.

Cheers, Gene Heskett
-- 
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 soap, ballot, jury, and ammo. Please use in that order."
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Re: [Emc-users] OT: analog to step/dir

[Gene Heskett]

On Thursday 13 April 2017 08:07:16 Eric Keller wrote:

> On Thu, Apr 13, 2017 at 2:43 AM, Dave Caroline
> 
>
> wrote:
> > You could get an analogue in connected to stepgen.N.position-cmd to
> > do this with any scaling needed. What is the use case?
>
> I have a data acquisition device that only puts out analog voltages. 
> I want to have it control a motor to follow a fairly small magnitude
> sine wave.  The actual amplitude isn't particularly important, but it
> has to stay within set limits and be reasonably repeatable.  I have a
> fairly tight budget, and the USDigital device would have been perfect.
>  I think they used a A/D converter with some sort of logic chips to
> generate step/dir.

If your budget is money, the siggen module is free, as is a sum2. The 
siggen may be able to do it all as it has lots of control pins. The sum2 
can have its individual input gains set to small, even negative values 
in order to subtract one input from the other. The a/d converter, 
depending on the interface card, might have to be an external, costs 
money item. I've not used that input mode myself, but IIRC some of the 
firmware for the Mesa cards can do a 12 bit a/d if thats (0-4095) enough 
resolution.  I do see a possible problem in "homing" the stepper though 
if it operates more than one turn from "zero" when in operation.

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Cheers, Gene Heskett
-- 
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 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 

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Re: [Emc-users] OT: analog to step/dir

[Eric Keller]

On Thu, Apr 13, 2017 at 8:29 AM, andy pugh  wrote:

> On 13 April 2017 at 13:07, Eric Keller  wrote:
> > I have a data acquisition device that only puts out analog voltages.
>
> It sounds like almost any motor would be easier to control in this
> application than a stepper motor.


Right now, I am trying a servo motor.  A lot of motors would be fine if I
could allow them to spin, but I can't.  Analog control without any feedback
is a problem, no doubt.
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Re: [Emc-users] OT: analog to step/dir

[andy pugh]

On 13 April 2017 at 13:07, Eric Keller  wrote:
> I have a data acquisition device that only puts out analog voltages.

It sounds like almost any motor would be easier to control in this
application than a stepper motor.

-- 
atp
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designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1916

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Re: [Emc-users] OT: analog to step/dir

[Eric Keller]

On Thu, Apr 13, 2017 at 2:43 AM, Dave Caroline 
wrote:

> You could get an analogue in connected to stepgen.N.position-cmd to do this
> with any scaling needed. What is the use case?
>

I have a data acquisition device that only puts out analog voltages.  I
want to have it control a motor to follow a fairly small magnitude sine
wave.  The actual amplitude isn't particularly important, but it has to
stay within set limits and be reasonably repeatable.  I have a fairly tight
budget, and the USDigital device would have been perfect.  I think they
used a A/D converter with some sort of logic chips to generate step/dir.
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Re: [Emc-users] OT: analog to step/dir

[andy pugh]

On 13 April 2017 at 01:53, Eric Keller  wrote:
>   USDigital used to have something called an
> "EPOT" but they got rid of it for some reason.

https://tinyurl.com/ke75fzx any good?

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1916

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Re: [Emc-users] OT: analog to step/dir

[Dave Caroline]

You could get an analogue in connected to stepgen.N.position-cmd to do this
with any scaling needed. What is the use case?

Dave Caroline

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