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Control digital output using nidaqmx in python

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Hello

 

I am new to the combination of python and NI Daqmx. I managed to downlaod all needed packages/libraries and want to controll 3 digital outputs using python.

I am aware that the page http://nidaqmx-python.readthedocs.io/en/latest/index.html

exists, however, the syntax there is unclear to me and I would need some examples in order to understand the syntax on that webpage.
I am familiar with C, C++, and Matlab.

 

System:

Device: NI USB-6008

Python 3.6.4 (using PyCharm)

Windows 7

 

What I want to control: port 0 line 0:2 as digital output

What should it do: Set digital output on or off in order to switch connected relais.

 

My questions:

1) How can I address a channel? e.g. port 0 line 0

2) How do I tell a channel whether it is input or output?

3) How do I tell the Daqmx that I want to switch the state (off -> on)?

 

Thank you very much for your attention and I am glad upon each feedback.

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Message 1 of 7
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Solution
Accepted by ucalmonte

Hi,

 

I think you will find this example helpful:

https://github.com/ni/nidaqmx-python/blob/master/nidaqmx_examples/do_sw_timed.py

Best Regards,
TK
Certified LabVIEW Architect (CLA)

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Message 2 of 7
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Hi,

 

thanks for the hint, however, in my opinion these examples are not that helpful for a beginner as there is no prober explanation of the code.

best regards

uc

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Message 3 of 7
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# Each port has 8 lines. This function will take each port it's activated lines.
# Assuming the lines start from 0 to 7
def activate_lines(mod_name, port1_lines, port2_lines, port3_lines):
sum_port1_line = 0
for i in range(0, len(port1_lines)):
val = port1_lines[i];
sum_port1_line += 2**val;

sum_port2_line = 0
for i in range(0, len(port2_lines)):
val = port2_lines[i];
sum_port2_line += 2**val;

sum_port3_line = 0
for i in range(0, len(port3_lines)):
val = port3_lines[i];
sum_port3_line += 2**val;

#Set all channels to output channels (standard configured as input at start-up of module)
# Module1, 2742xxxx
with nidaqmx.Task() as task:
task.do_channels.add_do_chan(mod_name + '/port0/line0:7')
task.do_channels.add_do_chan(mod_name + '/port1/line0:7')
task.do_channels.add_do_chan(mod_name + '/port2/line0:7')
List = [sum_port1_line, sum_port2_line, sum_port3_line]
print("Binary values for each port:")
print(List)
task.write(List)
time.sleep(0.200)
return


def get_lines_forSpecificCase(case_num):
return {
# CaseNum: [[port_0],[port1],[port2]]
# Keep in mind index starts from 0, I have 18 test cases in total with 20 relays to be controlled(0-17), in each case I have to control certain line with NI6501 

# so lets take case zero as an example, 0 : [[4], [1,6], [3]],  [4] means that I am making line 0.4 (port 0) high output and other lines are low and so on for the other ports(1,2)
0 : [[4], [1,6], [3]],
1 : [[4,5,6], [1,6], [3]],
2 : [[4], [1,6], [1,2,3]],
3 : [[1,2,4], [1,6], [3]],
4 : [[0,4], [1,6], [3]],
5 : [[4,7], [1,6], [3]],
6 : [[3,4], [1,6], [3]],
7 : [[3,4], [1,6], []],
8 : [[7], [1,6], [3]],
9 : [[4], [], [3]],
10: [[], [1,6], [3]],
11: [[4], [1,6], []],
12: [[7], [1,6], [0]],
13: [[4], [3], [1,2]],
14: [[5,6], [0,4], [3]],
15: [[7], [1,3,6,7], [0]],
16: [[7], [0,1,4,6], [0]],
17: [[1,2,7], [1,6], [0]],
}[case_num]

 

#Unique serial number NI digital I/O modules NI6501
serial_nr1 = 2742xxxx #Module 1 Hexadecimal number 1A28250
#find and assign the I/O modules to the correct Dev_numbers
system = nidaqmx.system.System.local()
a = system.driver_version
print(a)
print('')

 

device_dict = {} #empty dictionary for devices that are going to be found

for device in system.devices:
print(device.name)
print('Device Name: {0}, Product Category: {1}, Product Type: {2} Serial Number: {3}'.format(
device.name, device.product_category, device.product_type, device.dev_serial_num))
print('')
if device.dev_serial_num == serial_nr1:
device_dict['module1'] = device
print('I/O Module 1 with serial nr {0} assigned as {1}'.format(serial_nr1, device_dict['module1'].name))
print('')

test_cases_user_input = input("Type the case numbers in this format. eg: 1,2,3 .... 17 \n")
test_cases_user_input = test_cases_user_input.split(',')
# For each test case, we print all the lines
for i in range(0,len(test_cases_user_input)):
case_num = int(test_cases_user_input[i])
lines_port = get_lines_forSpecificCase(case_num)
print(get_lines_forSpecificCase(case_num))

 

Regards,

Murak ALmuairki,

Message 4 of 7
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Hi,

I have a similar problem using digital output to control a stepper motor in python.

 

System:

Windows 7, Python 3.7, NI USB-6009

 

The code:

import nidaqmx
import time
from nidaqmx.constants import (
    LineGrouping)

with nidaqmx.Task() as task:
	task.do_channels.add_do_chan('Dev1/port1/line0:3')
	task.start()
	while True:
		task.write([8,0,0,0])
		time.sleep(.002)
		task.write([0,8,0,0])
		time.sleep(.002)
		task.write([0,0,8,0])
		time.sleep(.002)
		task.write([0,0,0,8])
		time.sleep(.002)

 When running the code, the stepper motor will vibrate (presumably meaning that the writing to digital output works), but it will not rotate like I want it to. Any suggestions to fix this problem?

 

For reference, here is a version of the code in matlab that works like it is supposed to on the same computer/system:

 

clear all
close all
clc
pt=2/100;

s=daq.createSession('ni')
%%
addDigitalChannel(s,'Dev1','Port1/Line0','OutputOnly');
addDigitalChannel(s,'Dev1','Port1/Line1','OutputOnly');
addDigitalChannel(s,'Dev1','Port1/Line2','OutputOnly');
addDigitalChannel(s,'Dev1','Port1/Line3','OutputOnly');

n=0
while(n<100)
outputSingleScan(s,[1 0 0 0]);
pause(pt)
outputSingleScan(s,[0 1 0 0]);
pause(pt)
outputSingleScan(s,[0 0 1 0]);
pause(pt)
outputSingleScan(s,[0 0 0 1]);
pause(pt)
n=n+1
str='loop'
end

clear all
close all

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Message 5 of 7
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Thank you, this was very helpful to me.  For your stepper you might want to try using 8,2,4,1 in the write statement.  You have to do the bit field yourself.:

 

import nidaqmx
import time
from nidaqmx.constants import (
    LineGrouping)

with nidaqmx.Task() as task:
	task.do_channels.add_do_chan('Dev1/port1/line0:3')
	task.start()
	while True:
		task.write([8])
		time.sleep(.002)
		task.write([4])
		time.sleep(.002)
		task.write([2])
		time.sleep(.002)
		task.write([1])
		time.sleep(.002)

 

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Message 6 of 7
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I have the same error message WITH the sowftware controlled version ... any ideas ?

 

the exact error message is:

 

1 Channel 1 Sample Write:
Traceback (most recent call last):
File "ao_voltage_sw_timed.py", line 8, in <module>
print(task.write(1.0))
File "C:\Users\od_19\AppData\Local\Programs\Python\Python38\lib\site-packages\nidaqmx-0.5.7-py3.8.egg\nidaqmx\task.py", line 1169, in write
channels_to_write = self.channels
File "C:\Users\od_19\AppData\Local\Programs\Python\Python38\lib\site-packages\nidaqmx-0.5.7-py3.8.egg\nidaqmx\task.py", line 167, in channels
return Channel._factory(
File "C:\Users\od_19\AppData\Local\Programs\Python\Python38\lib\site-packages\nidaqmx-0.5.7-py3.8.egg\nidaqmx\_task_modules\channels\channel.py", line 118, in _factory
check_for_error(error_code)
File "C:\Users\od_19\AppData\Local\Programs\Python\Python38\lib\site-packages\nidaqmx-0.5.7-py3.8.egg\nidaqmx\errors.py", line 127, in check_for_error
raise DaqError(error_buffer.value.decode("utf-8"), error_code)
nidaqmx.errors.DaqError: Requested value is not a supported value for this property. The property value may be invalid because it conflicts with another property.
Property: DAQmx_AO_Max
Requested Value: 10.0
Maximum Value: 5.0
Minimum Value: 0.0
Channel Name: Dev1/ao0

Task Name: _unnamedTask<0>

Status Code: -200077

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Message 7 of 7
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