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WI-FI Stepper (WSX100)-SW behavior  

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Modelman
(@modelman)
Active Member
Joined: 3 months ago
Posts: 9
2020-08-05 9:00 pm  

Hi all,  I just got a WI-FI Stepper kit (WSX100) from Crowd Supply a couple of days ago.  Included with the kit is a board containing an ESP8266 MCU and a PowerStep01 driver, among other chips.  So far I have confirmed that all modes work with the supplied NEMA17 stepper motor.  However there is one issue that I have encountered with the SW Pin that I would like to run by anyone who has worked with the WSX100.

The goal of my project is to remotely control a stepper motor.  The stepper motor will turn a vacuum variable capacitor which will tune a small transmitting loop antenna to resonance.  To avoid accidental damage to the capacitor, I will stop the stepper motor when a limit switch is tripped.  The limit switch is connected to the SW Pin on the board.  According to the WSX100 documentation, the SW Pin is pulled to 3.3V when the limit switch is open, and the pin is pulled to ground when the switch is closed.  The data sheet (P13) for the PowerStep01 driver, from its manufacturer - ST Microelectronics, states that the SW Pin is pulled high by an internal 80K ohm resistor.  However I find that the resistance (with the WSX100 un-powered) between the SW Pin and Vcc is about 8M ohm, which results in the SW Pin reaching only about Vcc/2 when the limit switch is open;  current through the pull-up is insufficient to overcome leakage currents trying to pull the pin to ground.

I have attached an external 10K ohm pullup resistor to the SW Pin.  With the external resistor in place the SW Pin  gets pulled to Vcc within about a microsecond after the switch is open.  The state of the SW Pin ("switch") is correctly indicated on the browser.  Without the external resistor, opening the switch is insufficient for tripping the switch state from closed to open.  It appears that my WSX100 requires an external pullup resistor.

I would greatly appreciate if someone who has a WSX100 would run a test similar to what is described above to see if the state of the SW Pin could be cycled between closed, open, and back to closed by toggling the SW Pin from ground to float and back to ground without the inclusion of an external pull-up resistor.

It's no big deal if I have to use an external resistor.  I just want to determine if there is a discrepancy between  the actual hardware and what is written in the specifications.

Thanks much.

Modelman

 

 

 

 

 


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JoeLyddon
(@joelyddon)
Reputable Member
Joined: 1 year ago
Posts: 342
2020-08-06 5:36 am  

Look at all of Bill's videos on youtube...  Search Youtube for "dronebot steppers", etc.   He shows you exactly how to do it...

 

I think Paul McWhorter covers it too...  see page 28...

 

 

Have Fun,
Joe Lyddon

www.woodworkstuff.net


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Modelman
(@modelman)
Active Member
Joined: 3 months ago
Posts: 9
2020-08-06 2:46 pm  

@joelyddon

I watched Bill's video and read his presentation on the WSX100.  Bill does mention that the SW pin on the POWERSTEP01 has an internal pull-up resistor; I don't know if Bill confirmed that by measurement. 

Bill, if you are reading this post, please tell me if you have checked to see if the open SW Pin is pulled up to Vcc (3.3V). An internal pull-up resistor of 80K is specified in the POWERSTEP01 datasheet document (on page 13 of 92 pages).

What I'm looking for from forum members who have the WSX100 is whether their WSX100 has an internal pull-up resistor on the SW pin.  It appears that my SW pin does not have an 80K internal pull-up resistor.

Joe, please tell me where McWhorter addresses this issue.  I haven't found it.

Modelman

 


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JoeLyddon
(@joelyddon)
Reputable Member
Joined: 1 year ago
Posts: 342
2020-08-06 6:42 pm  

@modelman

Sorry, I missed that it was JUST for this...

I did a google search on it and found this...  Maybe there is something there that will help you...  (??)

  https://www.google.com/search?q=WSX100&oq=WSX100&aqs=chrome..69i57j69i60.4236j0j8&sourceid=chrome&ie=UTF-8

Thank you for letting us know how you make out, OK?

Later...  & have fun!

 

Have Fun,
Joe Lyddon

www.woodworkstuff.net


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