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step/direction before drivers

Posted by Ubermeisters 
step/direction before drivers
January 29, 2014 06:41PM
Hi all,
I have some servo motors that I would like to use for a 3d printer, the man who designed them has specified that in order to accomplish this, I need to wire them to the step/direction commands coming from the atmel, before the driver. These motors will be powered via a common hub, and feature eeprom/driver chips. I have ordered a sainsmart ramps 1.4, but due to either bad documentation, or my obvious lack of experience with electronics, I have been unable to figure out where I need to connect the motors to. Any feedback would be appreciated, please keep in mind that I am not terribly familiar with electronics in general.
Re: step/direction before drivers
January 30, 2014 12:00AM
for anyone who may wish to know, i believe i have found the relevant information, in the driver socket diagram provided by the Pololu chip.

[b.pololu-files.com]

now that i see this, i can also verify against the schematics listed on the wiki page for ramps 1.4

does anyone know if there are any additional steps i should be taking in my firmware (repetier) for this type of operation? if the board is epecting signal in one place or another, but not getting it due to the lack of a driver board, will that cause issues?
Re: step/direction before drivers
January 30, 2014 05:47PM
You only need to worry about the step/dir/enable pins, and they're all outputs. RAMPS and the attached Arduino won't be expecting anything from the drivers in that respect.

Just a note about firmware: If the drivers have opto-coupled inputs, they will require longer pulse lengths than the on-board drivers. You will need to configure this in your firmware (Marlin has it at least, I don't know about repetier).
Re: step/direction before drivers
January 31, 2014 12:39PM
The Manual for the control chip (driver) states the following:

Step and Direction Signal Timing
The step pulse should be a rising pulse with a duration of at least 0.2 microsecond. The direction signal should be stable for at least 6 microseconds from the rising edge of the step pulse.If you have an indexing system that does not hold the SDIR signal stable for at least 6 microseconds, you can fix it by running the direction signal into the D input of a D-style flip-flop and clocking the flip-flop with the rising edge of the step pulse.

The only good information i have found relating to step pulse length with repetier, is the following link, and to be completely honest, its way above me. this project is way above me as well, haha, but i am determined to make it work!

[forums.reprap.org]
Re: step/direction before drivers
January 31, 2014 12:59PM
[got them working] smiling smiley
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