I am reading data from a serial port, sent by an arduino.
I have two files, which I use separately to write some code and try differents things. In one of them, I read the data and I draw it using a matplotlib figure. After I finish using it, it remains connected to my computer and sending data. So, what i need to do is to "reset" the port. This is, close the opened port and open it again, and stop it from sending data so I can use the arduino to try some modifications in the code of this file.
So to accomplish this, i mean, to reset the port, i created another file and wrote this code:
import serial
print "Opening port"
try:
serial_port = serial.Serial("com4", 9600)
print "Port is open"
except serial.SerialException:
serial.Serial("com4", 9600).close()
print "Port is closed"
serial_port = serial.Serial("com4",9600)
print "Port is open again"
print "Ready to use"
But this code does not seems to work.The port is still connected and sending data. So, it means that I can not close the port with my code,and then reopen it again.
What am i doing wrong? How can I stop the arduino from sending data? Or how can I reset thw arduino, maybe?
Hope you can help me.
----- EDIT -----
I accomplish to identify the real problem that i am having, and it is not what i thought. The problem was not that the port was open despite that i use the closefunction that Pyserial have. The real thing is that the port is closing as I want, but the device (the arduino) is still sending data. So, i changed the code to reproduce the situation.
This is the code:
print "Abriendo puerto"
ser = serial
try:
ser = serial.Serial("com4", 9600, timeout = 1)
serial_port = "Open"
print "The port %s is available" %ser
except serial.serialutil.SerialException:
print "The port is at use"
ser.close()
ser.open()
while ser.read():
print "Sending data"
ser.setBreak(True)
time.sleep(0.2)
ser.sendBreak(duration = 0.02)
time.sleep(0.2)
ser.close()
time.sleep(0.2)
print "The port is closed"
exit()
With this code, what i do is:
1) I open the serial port
2) If the device is sending data, I print "Sending data"
3) After 1 sec, I try to close the port and stop the device from sending data
I tried these last two thing with the close function to close the port, and reading the docs I tried with setBreak and sendBreak as you can see in the code above (i left them on purpose). But the device is still sending the data, which means that the code does not work.
So, is there a way to tell the arduino "stop sending data", or can i reset the device?
I do a very similar thing, two ways with success.
The first way is to let the Arduino send data continuously. The problem here is when your python code wakes up and starts to read from the serial port, the Arduino might be anywhere in its procedures. The simple solution is to modify the Arduino code to send some kind of "restarting" line. All your python code needs to do in this case is wait for "restart", then read real data until it again sees "restart". I had noisy lines so my code read (and parsed) through multiple cycles to make sure it got good data.
resetCount = 0;
while resetCount < 3:
line = s.readline().rstrip("\r\n")
if string.find(line, "restart") != -1 :
resetCount += 1
elif resetCount > 0 :
fields = string.split(line, " ")
dict[fields[0]] = fields
The second way is to implement a command-response protocol with the Arduino, wherein the Arduino sends data only when requested. In this case your python code sends a command to the Arduino ("RT" in the example below) and then reads data from the Arduino until it sees a "completed" line or it times out.
dict = {}
regex = re.compile('28-[0-9A-Fa-f]{12}') # 28-000005eaa80e
s = serial.Serial('/dev/ttyS0', 9600, timeout=5)
s.write("RT\n");
while True:
line = s.readline().rstrip("\r\n")
print line
if string.find(line, "completed") != -1:
break;
fields = string.split(line)
if (regex.match(fields[0]) != None and len(fields) == 4) :
dict[fields[0]] = fields
s.close()
It is possible that when you close the port, data is still coming from the arduino and being buffered by the operating system. There is a short delay between your script calling close() and the device driver actually shutting stuff down.
An immediate re-open may allow the driver to carry on without resetting its buffer. This is the device driver buffer, not the one seen by the Python serial port instance.
If you wait for at least a couple of seconds after the call to close() before you try to call open() then the behaviour should be as you hope.
I have just spent most of the day working out that this is what had been preventing my code from working properly.
I think you have to do a serial_port.open() immediately after creation to actually open the port.
It also looks like it just opens the port and exits if successful. Maybe I'm missing something here. I've never used pySerial, I'm just going by the docs.
Try using the handle to close the port instead of invoking the constructor again.
If you the port is open and you call serial.Serial("com4", 9600) it will attempt to re-open the port again and fail.
If serial_port was assigned successfully then serial_port.close() should close it.
Related
I am writing a program to communicate between my laptop (Python) and an Arduino. The Arduino code, with which I have no issue, reads the serial data form my laptop and returns a reply. The code below works when I am calling the function which starts the serial communication from within the same file. However, when I import the file as a module in another file, using lal the same commands, it does not work!
To provide more detail, although Python thinks it has connected and even prints out the correct port number, it does not really connect. I know this because in the scenario that does work, when the serial communication is open, the Arduino IDE cannot speak to the Arduino as the Arduino is busy. However in the scenario which is not working, even after Python thinks it has opened serial communication, the Arduino IDE can still communicate with the Arduino.
Is there a way to pass the ser variable when called from a function in an imported module?
def connect():
for n in range(0,21):
try:
ser = serial.Serial('COM'+str(n), 115200 ,timeout=0.1)
status=1
port=n
return ser,port,status
except:
pass
time.sleep(0.05)
return 0, 0, 0
if __name__ == "__main__":
ser,port,status=connect()
n=0
while n<3:
num = input("Enter a word: ") # Taking input from user
ser.write(bytes(num, 'utf-8'))
time.sleep(0.05)
data = ser.readline()
print(data) # printing the value
n+=1
ser.close()
print('closed')
I have found the reason my code was not working! Notice in the code I posted, I use the input function to get a user input which is sent to the Arduino. This effectively results in a delay. In the scenario that was not working, I did not use the input function and so my code went straight from serial.serial to serial.write. The Arduino runs at 16 MHz and just couldn't keep up! All I needed to do was add a delay and now it works!
I'm having a weird issue with pyserial, using Python 3.6.9, running under WSL Ubuntu 18.4.2 LTS
I've set up a simple function to send GCODE commands to a serial port:
def gcode_send(data):
print("Sending: " + data.strip())
data = data.strip() + "\n" # Strip all EOL characters for consistency
s.write(data.encode()) # Send g-code block to grbl
grbl_out = s.readline().decode().strip()
print(grbl_out)
It sort of works, but every command I send is 'held' until the next is sent.
e.g.
I send G0 X0 > the device doesn't react
I send G0 X1 > the device reacts to G0 X0
I send G1 X0 > the device reacts to G0 X1
and so on...
My setup code is:
s = serial.Serial(com, 115200)
s.write("\r\n\r\n".encode()) # Wake up grbl
time.sleep(2) # Wait for grbl to initialize
s.flushInput() # Flush startup text in serial input
I can work around the delay for now, but it's quite annoying and I can't find anyone else experiencing the same. Any idea what could be causing this?
There might be a lot of problems here, but rest assured that the pyserial is not causing it. It uses the underlying OS's API to communicate with the UART driver. That being said you first have to test your code with real Linux to see whether WSL is causing it. I.e. whether a Linux and Windows UART buffers are correctly synced.
I am sorry that I cannot tell whether a problem is in your code or not because I do not know the device you are using, so I cannot guess what is happening on its end of communication channel. Have in mind that Windows alone can act weirdly in best of circumstances, so, prepare yourself for some frustrations here. Check your motherboard or USB2Serial converter drivers or whatever hw you are using.
Next thing, you should know that sometimes, communication gets confusing if timeouts aren't set. Why? Nobody really knows. So try setting timeouts. Check whether you need software Xon/Xoff turned on or not, and other RS232 parameters that might be required by the device you are communicating with.
Also, see what is going on with s.readline(), I wouldn't personally use it. Timeouts might help or you can use s.read(1024) with timeouts. I do not remember right now, but see whether pyserial supports asynchronous communication. If it does, you can try using it instead of standard blocking mode.
Also, check whether you have to forcefully flush the serial buffer after s.write() or add a sleep after it. It might happen that the device doesn't get the message but the read request is activated. As the device didn't receive the command it doesn't respond. After you send another command, IO buffer is flushed and the previous one is delivered and so forth. Serial communication is fun, but when it hits a snag it can be a real P in the A, believe me.
Ow, a P.S. Check whether the device sends "\r\n\r\n" or "\r\n" only, or "\r" or "\n" in response. s.readline() might get confused. For a start, try putting there two s.readline()s one after another and print out each output. If the device sends double EOL then the one s.readline() is stopping on the empty line and your program receives an empty response, when you send another command s.readline() goes through the buffer and returns a full line that is already there but not read before.
Here it goes. The code promissed in the comment. Big portions of it removed and error checks too.
It is a typing terminal for using PyS60 Python console on Nokia smartphones in the Symbian series via bluetooth. Works fantastically.
from serial import *
from thread import start_new_thread as thread
from time import sleep
import sys, os
# Original code works on Linux too
# The following code for gettin one character from stdin without echoing it on terminal
# has its Linux complement using tricks from Python's stdlib getpass.py module
# I.e. put the terminal in non-blocking mode, turn off echoing and use sys.stdin.read(1)
# Here is Win code only (for brevity):
import msvcrt
def getchar ():
return msvcrt.getch()
def pause ():
raw_input("\nPress enter to continue . . .")
port = raw_input("Portname: ")
if os.name=="nt":
nport = ""
for x in port:
if x.isdigit(): nport += x
port = int(nport)-1
try:
s = Serial(port, 9600)
except:
print >> sys.stderr, "Cannot open the port!\nThe program will be closed."
pause()
sys.exit(1)
print "Port ready!"
running = 1
def reader():
while running:
try:
msg = s.read()
# If timeout is set
while msg=="":
msg = s.read()
sys.stdout.write(msg)
except: sleep(0.001)
thread(reader,())
while 1:
try: c = getchar()
except Exception, e:
running = 0
print >> sys.stderr, e
s.write('\r\n\x04')
break
if c=='\003' or c=='\x04':
running = 0
s.write('\r\n\x04')
break
s.write(c)
s.close()
pause()
I'm trying to use hardware serial port devices with Python, but I'm having timing issues. If I send an interrogation command to the device, it should respond with data. If I try to read the incoming data too quickly, it receives nothing.
import serial
device = serial.Serial("/dev/ttyUSB0", 9600, timeout=0)
device.flushInput()
device.write("command")
response = device.readline()
print response
''
The readline() command isn't blocking and waiting for a new line as it should. Is there a simple workaround?
readline() uses the same timeout value you passed to serial.Serial().
If you want readline to be blocking, just delete the timeout argument, the default value is None.
You could also set it to None before calling readline(), if you want to have a timeout for openening the device:
import serial
try:
device = serial.Serial("/dev/ttyUSB0", 9600, timeout=0.5)
except:
#Exception handeling
device.flushInput()
device.write("command")
device.timeout=None
response = device.readline()
print response
I couldn't add a commend so I will just add this as an answer. You can reference this stackoverflow thread. Someone attempted something similar to your question.
Seems they put their data reading in a loop and continuously looped over it while data came in. You have to ask yourself one thing if you will take this approach, when will you stop collecting data and jump out of the loop? You can try and continue to read data, when you are already collecting, if nothing has come in for a few milliseconds, jump out and take that data and do what you want with it.
You can also try something like:
While True:
serial.flushInput()
serial.write(command)
incommingBYTES = serial.inWaiting()
serial.read(incommingBYTES)
#rest of the code down here
This is the code that reads from the z1 mote
while True:
if not ser.isOpen():
try:
ser = serial.Serial(z1port, z1baudrate,timeout=0, parity=serial.PARITY_NONE,
stopbits=serial.STOPBITS_ONE, bytesize=serial.EIGHTBITS)
except:
sys.exit("Error connecting device")
queue = ser.inWaiting()
if queue > 0:
data = ser.read(1000)
print data
time.sleep(0.2)
And this is the code that I have that I use it to write to the mote
# some event-driven code here so that whenever a message is received then do:
print(str(msg.payload))
ser = serial.Serial("/dev/ttyUSB1")
print ser.isOpen()
ser.write(msg.payload)
The output from the second code should be if msg.payload = "hello":
hello
True
But then the read code stops reading from the serial port (the code will run but no input). How do I solve this problem?
You can only create one serial connection to a device. The code in your question creates two connections, one in the main routine and one in the subroutine. In the main routine, you create a connection to establish communication with the device:
ser = serial.Serial(z1port, z1baudrate) # I assume z1port='/dev/ttyUSB1'
Then in your subroutine you also create a connection:
ser = serial.Serial("/dev/ttyUSB1")
So there are now two connections trying to use the same port. This will not work.
Instead, you should use the original connection throughout your program,
and define your subroutines to receive the connection as an input parameter. For example:
ser = serial.Serial(z1port, z1baudrate)
# do whatever to make connection to the device
getMessage(ser) # call subroutine to read data *with the existing connection*
ser.close() # close connection when finished
def getMessage(serConn):
# read data
data = serConn.read(1000)
# send ack
serConn.write(b'OK')
Another option is to open and close serial connections throughout your code, whenever you need to do communication. This is usually much less efficient, and only makes sense if there will only be intermittent communication with the device.
I used the idea by #mhopeng to write a code that implements multithreading programming, where one function handles the reading and the other handles the writing. And before they are both called, I will connect to the serial port and pass it to both of the threads.
I had to use multithreading because I needed a separate thread for writing at any time from the user input.
I am just wondering how the buffers work on a com port.. The code below is a snip of how I am reading a com port. I am wondering if by doing serial_connection.close() and serial_connection.open() I would be losing any data, or would it remain in the buffer? You might ask why I am closing and opening the comport.. The reason being is that it is actually a virtual port and for what ever reason when I stay connected to it for a length of time data stops transmitting...
import serial
serial_connection = serial.Serial(
port = self.SERIAL_PORT,
baudrate = self.BAUD_RATE,
timeout = 10
)
while true:
serial_connection.close()
serial_connection.open()
line = serial_connection.readline()
print line
PySerial has a separate thread that sits there listening for data to make sure that nothing gets lost. However, the OS itself does not buffer data. There is a slim chance that you could lose some data for the brief period of time between when you close the port and open it again.