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Is a microcontroller best for this?

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:

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. 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

Reply to
Eric R Snow
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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....

Reply to
BobG

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

Reply to
Sambo

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

Reply to
Eric R Snow

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

Reply to
Eric R Snow

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

Bye. Jasen

Reply to
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

Reply to
Eric R Snow

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.

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

Bye. Jasen

Reply to
jasen

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