Develop Reference

Adafruit MAX 31856 communicating with raspberrypi

I have been trying to read a thermocouple temperature on my raspberrypi however cant get the raspi to communicate with the adafruit MAX 31856. I have downloaded necessary libraries and checked that all connections are secure and correct however keep running into this error when I try to execute this code.
Any help is greatly appreciated!!
CODE
import board
import digitalio
import adafruit_max31856
spi = board.SPI()
cs = digitalio.DigitalInOut(board.D5)
cs.direction = digitalio.Direction.OTUPUT
thermocouple = adafruit_max31856.MAX31856(spi,cs)
print(thermocouple.temperature)
ERROR:
Traceback (most recent call last):
File "/home/pi/test4.py", line 6, in <module>
spi = board.SPI()
File "/usr/local/lib/python3.7/dist-packages/board.py", line 299, in SPI
return busio.SPI(SCLK, MOSI, MISO)
File "/usr/local/lib/python3.7/dist-packages/busio.py", line 289, in __init__
self._spi = _SPI(portId)
File "/usr/local/lib/python3.7/dist-packages/adafruit_blinka/microcontroller/generic_linux/spi.py", line 25, in __init__
self._spi = spi.SPI(device=(portid, 0))
File "/usr/local/lib/python3.7/dist-packages/Adafruit_PureIO/spi.py", line 167, in __init__
raise IOError("{} does not exist".format(device))
OSError: /dev/spidev0.0 does not exist
Code
Errors

Most probably there is a device driver loaded for spi0-0 and that removes /dev/spidev0.0 device.
check your /boot/config.txt for overlays loading MAX 31856 driver module.
if you want to use adafruit_max31856 lib you shouldn't be loading this driver. hope that helps

How to solve "control message failed, win error: A device which does not exist was specified" error PyUSB

I'm trying to connect a POS receipt printer to python and have been using python-escpos to do so. I'm running windows 10.
My code in my file 'print.py' is:
from escpos.printer import Usb
p = Usb(0x0456,0x0808)
p.text('Hello World\n')
but when i run it i get the following error log:
Traceback (most recent call last):
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\core.py", line 223, in get_interface_and_endpoint
return self._ep_info[endpoint_address]
KeyError: 1
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "print.py", line 5, in <module>
p.text('Hello World\n')
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\escpos\escpos.py", line 437, in text
self._raw(txt.encode())
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\escpos\printer.py", line 73, in _raw
self.device.write(self.out_ep, msg, self.timeout)
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\core.py", line 940, in write
intf, ep = self._ctx.setup_request(self, endpoint)
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\core.py", line 102, in wrapper
return f(self, *args, **kwargs)
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\core.py", line 215, in setup_request
intf, ep = self.get_interface_and_endpoint(device, endpoint_address)
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\core.py", line 102, in wrapper
return f(self, *args, **kwargs)
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\core.py", line 225, in get_interface_and_endpoint
for intf in self.get_active_configuration(device):
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\core.py", line 102, in wrapper
return f(self, *args, **kwargs)
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\core.py", line 239, in get_active_configuration
bConfigurationValue=self.backend.get_configuration(self.handle)
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\backend\libusb0.py", line 510, in get_configuration
100)
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\backend\libusb0.py", line 593, in ctrl_transfer
timeout
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\backend\libusb0.py", line 431, in _check
raise USBError(errmsg, ret)
usb.core.USBError: [Errno None] b'libusb0-dll:err [control_msg] sending control message failed, win error: A device which does not exist was specified.\r\n\n'
Does anyone know what i need to do to make this work.
I have installed libusb into my System32 and SysWOW64 folders, aswell as installing a libusb-32 driver for my printer with zadig.
The printer i'm using is a 'Hoin 58mm POS Printer'.
I would be grateful if someone could explain to me why i'm having this error and how to solve it!

Firstly, you can check this link for the complete thread.
As suggested by KM4YRI,
I ran into the same No backend available exception when trying to follow the tutorial on a Windows 7 machine. The following worked for me, per one of the StackOverflow replies:
1. Download the latest Windows binary: https://sourceforge.net/projects/libusb/files/libusb-1.0/libusb-1.0.21/libusb-1.0.21.7z/download
2. Unzip using 7zip into a temp dir
3. If on 64-bit Windows, copy `MS64\dll\libusb-1.0.dll` into `C:\windows\system32`. If on 32-bit windows, copy `MS32\dll\libusb-1.0.dll` into `C:\windows\SysWOW64`.
I've verified the above answer on Windows-10 64-bit version.

I had a tight experience with that error using at least 3 different USB Storage Devices. After hours of trials I ended up to a feeling that USB transmission errors are the cause of this error.
The USB bus will return it in a random pattern for a low quality connection as if a device remove has presumably happened.
In my scenario I was bulk writing sectors to a \\.\PhysicalDriveN device and I noticed that after a short period the connection reestablished and the file handle was still valid and going.
To overcome the error I've ended up with the following steps:
Seek To File Position;
Write Sector;
For any 433 error:
250 ms delay;
Seek To file Position, ignoring ERROR_NO_SUCH_DEVICE and ERROR_NOT_READY errors and trying for at least 1000 ms before giving up;
Read Sector, ignoring ERROR_NO_SUCH_DEVICE and ERROR_NOT_READY errors and retrying for up to 1000 ms before giving up;
Specially for my scenario: I've compared input buffer and read buffer and stop if matching;
Repeat the whole procedure up to 5 times.
So the idea here is the following: The device driver returns ERROR_NO_SUCH_DEVICE assuming a device remove scenario, but still in a pending state. As the problem is simply quality of physical connection, the link continues and the bus driver starts a renegotiation, in which case a ERROR_NOT_READY is temporarily returned. When the link is stable and negotiated, communication continues without the need to reopen the device handle.

I would recommend adding a sleep statement of a second or two in between the instantiation of the USB printer, and the attempt to print to it. e.g:
from escpos.printer import Usb
from time import sleep
p = Usb(0x0456,0x0808)
sleep(1)
p.text('Hello World\n')

Timeout error with PyVISA -- communicating with Agilent 34970A throug RS232 (USB)

This is my first time i try to use Pyvisa, in order to communicate with an Agilent 34970A, using a RS232 connection(using an USB port).
This is what's happening to me, inserting the basic first lines:
IN: import visa
IN: rm=visa.ResourceManager()
IN: print rm.list_resources()
(u'ASRL4::INSTR',)
IN: inst=rm.open_resource("ASRL4::INSTR")
IN: print inst.query("*IDN?")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "C:\Anaconda2\lib\site-packages\pyvisa-1.8-py2.7.egg\pyvisa\resources\messagebased.py", line 407, in query
return self.read()
File "C:\Anaconda2\lib\site-packages\pyvisa-1.8-py2.7.egg\pyvisa\resources\messagebased.py", line 332, in read
message = self.read_raw().decode(enco)
File "C:\Anaconda2\lib\site-packages\pyvisa-1.8-py2.7.egg\pyvisa\resources\messagebased.py", line 306, in read_raw
chunk, status = self.visalib.read(self.session, size)
File "C:\Anaconda2\lib\site-packages\pyvisa-1.8-py2.7.egg\pyvisa\ctwrapper\functions.py", line 1582, in read
ret = library.viRead(session, buffer, count, byref(return_count))
File "C:\Anaconda2\lib\site-packages\pyvisa-1.8-py2.7.egg\pyvisa\ctwrapper\highlevel.py", line 188, in _return_handler
raise errors.VisaIOError(ret_value)
pyvisa.errors.VisaIOError: VI_ERROR_TMO (-1073807339): Timeout expired before operation completed.
This timeout error happens everytime i try to read a value. I imposed also a larger timeout but nothing, i waited some minutes in vain. Any idea for this problem?

You need to match up your baud rate. Either on your 34970A or in the attributes of pyVisa.
The default that comes with visa is 9600.
https://buildmedia.readthedocs.org/media/pdf/pyvisa/master/pyvisa.pdf
here's an example if you wanted to change it to 115200, the highest baud on the 34970A.
inst = rm.open_resource('ASRL4::INSTR')
inst.baud_rate = 115200

Try changing the RS232 setting protocol to be XON/XOFF.

Using numdisplay, "An existing connection was forced to close by the remote host"

I've been learning to use python in astronomy and for that I'm following this notes. In the very beginning the author does the following example:
>>> im = pyfits.getdata('http://das.sdss.org/www/cgi-bin/drC?RUN=3630&RERUN=40&CAMCOL=3&FIELD=83&FILTER=r')
>>> numdisplay.display(im,z1=1000,z2=1500)
I try to replicate it and I get:
>>> numdisplay.display(im,z1=1000,z2=1500)
Image displayed with Z1: 1000 Z2: 1500
Traceback (most recent call last):
File "<pyshell#13>", line 1, in <module>
numdisplay.display(im,z1=1000,z2=1500)
File "C:\Mine\Python\lib\site-packages\numdisplay\__init__.py", line 446, in display
_d.writeImage(bpix,_wcsinfo)
File "C:\Mine\Python\lib\site-packages\numdisplay\displaydev.py", line 513, in writeImage
self.writeData(_lx,_ydisp,_fpix[block,:])
File "C:\Mine\Python\lib\site-packages\numdisplay\displaydev.py", line 379, in writeData
self._writeHeader(opcode,self._MEMORY, -nbytes, x, y, frame, 0)
File "C:\Mine\Python\lib\site-packages\numdisplay\displaydev.py", line 542, in _writeHeader
self._write(a.tostring())
File "C:\Mine\Python\lib\site-packages\numdisplay\displaydev.py", line 580, in _write
nwritten = self._socket.send(s[-n:])
error: [Errno 10054] An existing connection was forced to close by the remote host
I don't understand what I'm doing wrong. I mean if I write numdisplay.open() everything is fine... I'm thinking that it might be my antivirus or something that doesn't let python to communicate with ds9... Can somebody help me?
Edit: Well it doesn't seem to be the antivirus. I stopped it and run the script and I got the same error.

I was getting similar error messages, and I just tried adding a non-'None' argument to the bufname argument and it works (my image is about 4096.4096):
numdisplay.display(data,bufname='imt4096')

NI-VISA 5.1.2 + python 2.7 + OS 10.6.8 TCPIP ERROR

I have a Keithley 2701 DMM and I am trying to communicate with it via TCPIP using python 2.7 and pyVISA. I am running python 2.7 with virtualenv and wxPython. I know the device is active because I can ping the IP address, I am trying to access the machine using the following code:
from pyvisa.vpp43 import visa_library
visa_library.load_library("/Library/Frameworks/Visa.framework/VISA")
import visa import instrument
Keithley = visa.instrument("TCPIP::192.168.0.2::INSTR")
when I run the code I get the following error:
Traceback (most recent call last):
File "Keithley.py", line 4, in <module>
Keithley = visa.instrument("TCPIP::192.168.0.2::INSTR")
File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/PyVISA-1.4-py2.7.egg/pyvisa/visa.py", line 294, in instrument
return Instrument(resource_name, **keyw)
File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/PyVISA-1.4-py2.7.egg/pyvisa/visa.py", line 358, in __init__
"lock")))
File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/PyVISA-1.4-py2.7.egg/pyvisa/visa.py", line 132, in __init__
keyw.get("lock", VI_NO_LOCK))
File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/PyVISA-1.4-py2.7.egg/pyvisa/vpp43.py", line 753, in open
byref(vi))
File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/PyVISA-1.4-py2.7.egg/pyvisa/vpp43.py", line 398, in check_status
raise visa_exceptions.VisaIOError, status
pyvisa.visa_exceptions.VisaIOError: VI_ERROR_RSRC_NFOUND: Insufficient location information or the requested device or resource is not present in the system.
Any help will be greatly appreciated....
V

I have not played with this particular DMM, but I have connected to several other devices using your same setup.
1) Check your documentation / DMM to ensure that the board number is in fact zero. Otherwise you'll need to change the following line:
Keithley = visa.instrument("TCPIP::192.168.0.2::INSTR")
To something more like
Keithley = visa.instrument("TCPIP1::192.168.0.2::INSTR")
2) Try to use a raw SOCKET connectional rather than the typical INSTR method.
NI Socket Examples
Keithley 2701 Examples
If I can dream up anything else I will update my response.