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I used to have a 15 deg stepper motor; now I have a 7.5 deg stepper motor.

The ideal thing is to change the software to output the pulse control at double the rate to achieve the same rotation rate. But b/c I don't have the software source I can't easily change it.

To avoid this issue , I would like to create some HW that goes inline with the existing control output that will issue two pulses for each incoming pulse.

Delay based solutions for frequency doubling don't seem to be a good solution as their delay element would have to vary for each input frequency.

Is a PLL a good option? A small micro-controller? Any other suggestions?

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  • \$\begingroup\$ Doubling the pulse won't give you any increased resolution over the \$15^\circ\$ motor. Doubling the pulse can also become tricky as you need to know that your second pulse isn't going to bleed into the first. PLL won't help you as that is for continuous frequencies not control signals. A simple edge detector would probably work, but first more information would be useful. What stepper motor drivers are you using? How are they wired up? \$\endgroup\$ – Tom Carpenter Aug 22 '15 at 17:24
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    \$\begingroup\$ Use a 1:2 gearbox. \$\endgroup\$ – Andy aka Aug 22 '15 at 17:37
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You could use a small microcontroller which doesn't require much external circuitry. One such option is a 8-pin PIC10F200 from Microchip. It's available in 8-pin DIP and 8-pin or 6-pin surface mount packages. It just needs VCC and GND, all remaining pins can be used as GPIO. It's self-timed with a reasonable accuracy, so it doesn't even need a crystal. Using a microcontroller gives you a nice amount of flexibility for solving the problem.

http://www.microchip.com/wwwproducts/Devices.aspx?product=PIC10F200

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