Is a microcontroller best for this?

[Eric R Snow]

Greetings All,
I want to build a stepper driven pointer. US Digital sells a chip that
uses the signals from an encoder to output step and direction signals.
Hers's a link: http://www.usdigital.com/products/ls7183-ls7184/ . The
step and direction signals can then be used with another chip, the
UCN5804B for example, to drive a stepper motor. I have built the
circuit and it works well at low speeds. I can spin the encoder too
fast for the stepper to keep up. The top continuous speed of the
stepper is about 1500 ppm. But short, maybe 200 steps maximum, speeds
of 6000 ppm might be encountered. I know this is slow for a 400 step
motor but I'm worried that I might lose a couple steps when reversing
at high step rates. So I'm wondering if a buffer might be in order and
if a microcontroller would be the best device for this. I'm going to
go ahead and build the mechanical part of this. But if the system
loses steps I'd like to have some idea of what to do next.
Thanks,
Eric R Snow

 

[BobG]

I think the answer is 'current mode'... info on the MicroMo and
FraunHofer sites.... run the stepper from a real high voltage and a
series resistor... when the V switches on, a big hi voltage pulse
starts the current flowing, then decays back. 1000s of steps/sec
possible in their graphs....

 

[Sambo]

Greetings All,
I want to build a stepper driven pointer. US Digital sells a chip that
uses the signals from an encoder to output step and direction signals.
Hers's a link: http://www.usdigital.com/products/ls7183-ls7184/ . The
step and direction signals can then be used with another chip, the
UCN5804B for example, to drive a stepper motor. I have built the
circuit and it works well at low speeds. I can spin the encoder too
fast for the stepper to keep up. The top continuous speed of the
stepper is about 1500 ppm. But short, maybe 200 steps maximum, speeds

what are you powering with this ( 1 Kg disk for example? )

of 6000 ppm might be encountered. I know this is slow for a 400 step

motor but I'm worried that I might lose a couple steps when reversing

Are you building XY table where it matters.

at high step rates. So I'm wondering if a buffer might be in order and
if a microcontroller would be the best device for this. I'm going to
go ahead and build the mechanical part of this. But if the system
loses steps I'd like to have some idea of what to do next.
Thanks,
Eric R Snow

At over 3 dollars I'd be prone to go for a PIC because as a byproduct
I'd end up with some code I can hopefully use if I have to use different
motors in the future or for a similar project, (but I am setup for it.)

Cheers, Sam

 

[Eric R Snow]

what are you powering with this ( 1 Kg disk for example? )

Are you building XY table where it matters.

At over 3 dollars I'd be prone to go for a PIC because as a byproduct
I'd end up with some code I can hopefully use if I have to use different
motors in the future or for a similar project, (but I am setup for it.)

Cheers, Sam

Greetings Sam,
I'm only powering a needle about 1.5 inches long. My goal is to
emulate a mechanical dial indicator. It's very hard for me to watch
the digital display to gauge travel when the numbers are changing
rapidly. So I'm thinking that by using the output from the scales on
my machines I can have an analog display as well as the digital
display.
Thanks,
Eric

 

[Eric R Snow]

I think the answer is 'current mode'... info on the MicroMo and
FraunHofer sites.... run the stepper from a real high voltage and a
series resistor... when the V switches on, a big hi voltage pulse
starts the current flowing, then decays back. 1000s of steps/sec
possible in their graphs....

Thanks Bob. I have driven steppers with this method in the past but
had completely forgotten about it.
Eric

 

[jasen]

I'm only powering a needle about 1.5 inches long. My goal is to
emulate a mechanical dial indicator. It's very hard for me to watch
the digital display to gauge travel when the numbers are changing
rapidly. So I'm thinking that by using the output from the scales on
my machines I can have an analog display as well as the digital
display.

If you've got PWM output to spare use it to drive an ordinaryy needle
indicator.

Bye.
Jasen

 

[Eric R Snow]

If you've got PWM output to spare use it to drive an ordinaryy needle
indicator.

Bye.
Jasen

Greetings Jasen,
How do I position the needle exactly with PWM? With the encoder setup
I have now the scales output 5 pulses per .001" travel. Using the
aforementioned chips,a stepper motor, and the proper gearing the
indicating needle sweeps .100" with 500 steps. This results in .0002"
resolution. I really don't need the indicator to be that fine because
I use the digital display for exact positioning. However, all the
steps make for smoother motion of the needle. Will PWM do this also?
Fairly simply? I'm open to other methode.
Cheers,
Eric

 

[jasen]

Greetings Jasen,
How do I position the needle exactly with PWM?

you have to calculate how far you want the needle positioned at and then
set the pwm to a proportional level.

what you do is rig your meter up as a voltmeter that reads full scale when
the the supply voltage is applied to it then just hook it to the PWM output,

then just set the pwm's output compare register to whatever fraction of full
you want and turn the pwm circuit in the microcontroller on, hanve have the
meter attached to the appropriate output and the meter needle will go to the
corresponding poosition on the dial.

a small capacitor across the meter movement can help is there's any wiggle
left after the pwm.

With the encoder setup
I have now the scales output 5 pulses per .001" travel. Using the
aforementioned chips,a stepper motor, and the proper gearing the
indicating needle sweeps .100" with 500 steps. This results in .0002"
resolution. I really don't need the indicator to be that fine because
I use the digital display for exact positioning. However, all the
steps make for smoother motion of the needle. Will PWM do this also?
Fairly simply? I'm open to other methode.

if you have the hardware working stick with it... no point junking
soomething that works.

Bye.
Jasen