using a stepper motor

[peekaybee]

Hi There,
I am a newbie so please forgive me.
I have to learn python fast for a project and I need to control a stepper motor.
I use the command import usb.core
but I just get the NameError: name 'usb" is not defined
how can I import the usb.core?
thank you

[joan]

Windows or Linux?

[peekaybee]

Linux I guess....
I have a RaspberryPi 2
Should I use python 2 or 3
IDLE?

in a nutshell this is what I am trying to do

control a moving slit (aperture)
display a sequence of images on a screen.
open and close a shutter

1) Home the aperture
variables are: width of aperture (2,3,or 4mm)
distance aperture travels (= number of exposures).

2) display image

3 initial wait time (1min to 30min)

4) open shutter (exposure time 10 secs to 2 mins approx)

5) close shutter

6) advance aperture (2,3 or 4mm)

7) advance image

8) frame settle time (prob about a min)

repeat stages 4 to 8 twenty to sixty times

easy peasy right?

I have got the pi, control board, stepper motor and shutter

[danjperron]

What kind of stepper?

What is your control board?

Maybe an A4998 stepper controller will be easier.

[peekaybee]

Hi there
have a got a stepperbee+ control board and the large stepper motor that goes with it.
pc-control.co.uk
they supplied some code to go with it but get the error message as before.

[danjperron]

I check the website and looks like the stepper b+ is for a X86 windows operating.

Unless they have the driver for linux arm, you won't be able to use it.

Check for a A4998 stepper driver.

[ghp]

Hello,
I browsed the website of the company, and hidden somewhere I found the page about connecting to raspberry.
If your python source file is named 'usb.py', this could cause the error. Just rename it to something else.
And did you install pyusb ?

sudo apt-get update
sudo apt-get install python-pip
sudo pip install pyusb

Hope this helps.
Gerhard

[danjperron]

I browsed the website of the company, and hidden somewhere I found the page

Do you have the link of that hidden webpage ?

[joan]

http://pc-control.co.uk/control/raspi/r ... perbee.php

[peekaybee]

sudo apt-get update
sudo apt-get install python-pip
sudo pip install pyusb

tried running this and I just get the invalid syntax message

[davef21370]

Can you post your code?
Be sure to put it between the code tags in the editor so it looks something like...

Code: Select all

if my_code == dodgy:
    seek_help()

Dave.

[peekaybee]

$ sudo apt-get install pyusb
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package pyusb

[peekaybee]

o.k have downloaded the pyusb programe
but can't seem to install it

this is from the terminal window. The pyusb programme is in downloads

pi@raspberrypi ~ $ sudo apt-get install pyusb
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package pyusb
pi@raspberrypi ~ $ sudo apt-get install pyusb
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package pyusb
pi@raspberrypi ~ $ sudo apt-cache search pyusb
python-usb - USB interface for Python
pi@raspberrypi ~ $

How do I instruct the pi to find and install the programme that is now in downloads?
Any help greatly appreciated.
cheers

[ghp]

Hello,
I got a barcode scanner connected to python and then to scratch.

The usual pyusb-install did not workwith „pip install pyusb“. This resulted in a ‘backend not found’ exception and „undefined symbol: libusb_strerror“
When I tried to download walac-pyusb-50b1490 from https://github.com/walac/pyusb, this worked, but I had to uninstall the pip-installed code first „sudo pip uninstall pyusb“.

The needed backend packages are already available in raspbian, you can check this with
apt-cache pkgnames | grep libusb

You should find libusb-1.0-0 in the list.

Good luck,
Gerhard

[peekaybee]

o.k found that & installed!
thank you for your help, I will try this out now!

[ghp]

Hello,

think this is the 'hello world' for USB.
Is from the pyusb code. Should list up all your connected devices and when this works, most of trouble is solved ? upfront ?

Regards,
Gerhard

Code: Select all

import usb.core
import usb.util

devices = usb.core.find(find_all=True)

for p in devices:
    print( p)

[peekaybee]

brilliant. can now see the product is there. just got to control it now!
thanks for your help

[peekaybee]

import usb.core
import usb.util

devices = usb.core.find(find_all=True)

for p in devices:
print( p)
I can see the device

Screen Shot 2015-07-31 at 10.14.30.png (38.82 KiB) Viewed 2004 times

but if I try and run the supplied script I get the error message

Screen Shot 2015-07-31 at 11.56.57.png (11.1 KiB) Viewed 2004 times

and if I type (or copy and paste the script into idle) the “if dev is None” line, the “None” is purple rather than orange.

I have tried this both in Python & Python3


Any help greatly appreciated.

[ghp]

Code: Select all

if dev == None:
    raise ....
else:
   do something else...

Think the 'is None' is not correct ?

Regards,
Gerhard

[peekaybee]

still cant get this code to run:

import usb.core

dev = usb.core.find(idVendor=0x04d8, idProduct=0x005d)

if dev is None:
raise ValueError('Device not found')
else:
try:
dev.detach_kernel_driver(0)
except:
pass
dev.set_configuration()

timeLSB = 100
timeMSB = 1
stepsLSB = 50
stepsMSB = 1
direction = 1
outputs = 0b00000110

data=[2, direction, timeLSB, timeMSB, stepsLSB, stepsMSB, outputs]
dev.write(2,data)
if I run it in idle it says : ValueError: Device not found.
if I write it in the shell, I get as far as the command except: which it describes as "invalid syntax"
I tried writing both dev == None: & dev is None: with the same conclusion.
The device is connected and visible.

any help greatly appreciated

[ghp]

Hello,
could you place code-tags around your code in the post above ? Makes it easier to read it.
see viewtopic.php?f=32&t=84477
Regards,
Gerhard

Then, place a "print (dev)" in the line before the "if dev is None:"-line. Just to see what is going on.

[peekaybee]

Is this o.k?

Code: Select all

import usb.core

dev = usb.core.find(idVendor=0x04d8, idProduct=0x005d)

if dev is None:
    raise ValueError('Device not found')
else:
    try: 
        dev.detach_kernel_driver(0)
    except:
        pass
    dev.set_configuration()

    timeLSB = 100
    timeMSB = 1
    stepsLSB = 50
    stepsMSB = 1
    direction = 1
    outputs = 0b00000110

    data=[2, direction, timeLSB, timeMSB, stepsLSB, stepsMSB, outputs]
    dev.write(2,data)

[peekaybee]

if I type: sudo idle into the terminal window before running the command in the idle environment, I don't get any error messages but a restart in the python prompt.

[peekaybee]

Screen Shot 2015-08-02 at 14.46.38.png (51.79 KiB) Viewed 1770 times

The attachment Screen Shot 2015-08-02 at 14.46.38.png is no longer available

with print (dev) included

[ghp]

Hello, have added some code which I found to work.
Best approach is to copy the code to a leafpad window, and save it to a file, say 'test.py'
Then, in a terminal window, run it by "python test.py".
If there are errors in console. mark them and copy paste here.

Code: Select all

import usb.core
import usb.util


dev = usb.core.find(idVendor=0x04d8, idProduct=0x005d)
print (dev)


if dev is None:
    raise ValueError('Device not found')
else:
    if dev.is_kernel_driver_active(0) is True:
        # tell the kernel to detach
        dev.detach_kernel_driver(0)
        # claim the device
        usb.util.claim_interface(dev, 0)
        
    # most possibly this thing has only one configuration
    # so no need to set it
    # dev.set_configuration()

    timeLSB = 100
    timeMSB = 1
    stepsLSB = 50
    stepsMSB = 1
    direction = 1
    outputs = 0b00000110

    data=[2, direction, timeLSB, timeMSB, stepsLSB, stepsMSB, outputs]
    dev.write(2,data)