Python Serial How Many Lines to Read?
Python Datalogger - Using pySerial to Read Series Information Output from Arduino
After I became skillful with Arduino I establish myself trapped in its evolution environment (IDE). I needed to escape from the simplicity of the serial port and transform the platform into a usable engineering tool. I tried saving to SD cards, only decided adding more than hardware was superfluous; I tried Bluetooth and WiFi, but over again, barring specific Internet of Things applications, I found those to exist roundabout ways of achieving what I wanted: a simple datalogging system. I ultimately arrived at Python's pySerial library, which reads direct grade the serial port and was a complete solution to my predicament.
Using pySerial is much easier than one might wait, as the most fundamental implementation consists of merely three lines of lawmaking:
import serial ser = serial.Serial('/dev/ttyACM0') ser_bytes = ser.readline()
These three simple lines read a unmarried row of data from the serial port. In the example of Raspberry Pi, the serial port (on my Arduino) is located at '/dev/ttyACM0'. You may also find yours there, or at an integer increment (ttyACM1, ttyACM2, etc.), or peradventure a different address completely. Check your Arduino IDE serial port for the exact location. Afterwards successfully reading a line from your Arduino, verify that information technology is in the desired format. I chose to impress and read a unmarried line, merely yous may prefer comma separated or like formats. The code above isn't particularly interesting, merely it verifies that pySerial is working and that you are parsing information correctly from your serial port. In one case the method above is understood, nosotros can advance onto loops and recording information in existent-time.
NOTE: I volition exist using a DHT11 temperature sensor to produce data on the Arduino stop. Since this is a tutorial on reading data from the serial port using Python, not Arduino, I recommend visiting a DHT11 tutorial to larn how to print temperature information from the sensor to the series port (see here, or here).
Serial Read Loop
I volition be using a while loop and keyboard interrupt (CTL-C) to loop and halt the datalogging. The data from the series port likewise needs to be converted from unicode to float (or another datatype) so that the data tin be processed in Python. In my instance, I am using "utf-8" to decode, which is Arduino'south default encoding and the near normally used character encoding format. You may also notice the 'ser.flushInput()' command - this tells the serial port to clear the queue then that data doesn't overlap and create erroneous information points. Sometimes the conversion via float() can create errors, but this is due to overprinting from the Arduino'due south end. If you receive such an error, restart the python script and try again.
import serial ser = serial.Serial('/dev/ttyACM0') ser.flushInput() while Truthful: try: ser_bytes = ser.readline() decoded_bytes = float(ser_bytes[0:len(ser_bytes)-2].decode("utf-8")) print(decoded_bytes) except: print("Keyboard Interrupt") break
Now we accept a working existent-time data printer in Python. Decidedly, this isn't particularly interesting because we aren't saving or plotting the data, and so nosotros'll cover how to do both of those adjacent.
Saving Serial Data to CSV File
In the code below I have implemented a style to salvage the serial information in real-time to a .csv file.
import serial import time import csv ser = series.Series('/dev/ttyACM0') ser.flushInput() while True: try: ser_bytes = ser.readline() decoded_bytes = float(ser_bytes[0:len(ser_bytes)-2].decode("utf-eight")) print(decoded_bytes) with open up("test_data.csv","a") every bit f: writer = csv.writer(f,delimiter= ",") writer.writerow([time.time(),decoded_bytes]) except: print("Keyboard Interrupt") break
At present we accept a working datalogger! This is every bit uncomplicated every bit information technology gets, and it's remarkably powerful. The iii lines that outset as: '' with open("test_data.csv","a") every bit f: '' look for a file chosen 'test_data.csv' and create information technology if it doesn't exist. The "a" in parentheses tells Python to suspend the serial port information and ensure that no data is erased in the existing file. This is a k result because information technology not only takes intendance of saving the information to the .csv file, merely it creates one for united states of america and prevents overwriting and (most times) abuse. How considerate!
Live Plotting Serial Data Using matplotlib
To take things a bit farther, I decided to aggrandize the content here and include a real-time plot. I observe existent-time plotting a useful tool when acquiring data of any kind. It is much easier to find faults in visualizations than information technology is to discover them in streaming values.
NOTES: while I was using Raspberry Pi, I came across an issue betwixt reading the serial port, saving to .csv, and updating the plots. I institute that updating the plot occupied a lot of processing time, which resulted in slower reading of the serial port. Therefore, I advise anyone who is using the method below to assess whether you are reading all the bytes that are being outputted by the Arduino. I establish that I was missing bytes or they were getting backed upwards in the queue in the buffer. Do some tests to verify the speed of your loop. This will prevent lost bytes and dropouts of data. I found that my loop took roughly half a second to complete, which means that my serial port should non be outputting more than 2 points per second. I actually used 0.8 seconds as the time betwixt data records and it appeared to grab all information points. The wearisome loop is a result of the plotting, so once you annotate out all of the plot code, you will get a much higher information rate and .csv save rate (just as higher up).
import serial import fourth dimension import csv import matplotlib matplotlib.use("tkAgg") import matplotlib.pyplot as plt import numpy as np ser = serial.Series('/dev/ttyACM0') ser.flushInput() plot_window = 20 y_var = np.array(np.zeros([plot_window])) plt.ion() fig, ax = plt.subplots() line, = ax.plot(y_var) while True: try: ser_bytes = ser.readline() endeavour: decoded_bytes = float(ser_bytes[0:len(ser_bytes)- 2].decode("utf-viii")) print(decoded_bytes) except: continue with open("test_data.csv","a") as f: writer = csv.writer(f,delimiter= ",") writer.writerow([time.time(),decoded_bytes]) y_var = np.suspend(y_var,decoded_bytes) y_var = y_var[1:plot_window+ 1] line.set_ydata(y_var) ax.relim() ax.autoscale_view() fig.canvas.describe() fig.canvass.flush_events() except: print("Keyboard Interrupt") break
Figure ane: DHT11 Live Plot from Serial Port
Plot produced by matplotlib in Python showing temperature information read from the serial port. During this plot, the sensor was exposed to a oestrus source, which can be seen hither every bit an increment from 31 to 35 degrees C.
Conclusion
This tutorial was created to demonstrate that the Arduino is capable of acting every bit an independent information logger, separate from wireless methods and SD cards. I found Python's pySerial method a while agone, and I wanted to share its capabilities with makers and engineers that may exist having the same problems that I was encountering. Printing data to Arduino'south series port and then reading it through Python gives the user the liberty to investigate the data farther, and have reward of the advanced processing tools of a figurer, rather than a micro controller. This method likewise allows the user to span the gap betwixt live data and laboratory measurements. With existent-fourth dimension datalogging via the series port, i tin can mimic the laboratory setup of acquisition, analysis, and live observation. Often, with Arduino the user is trapped in the series port, or is relegated to communication via protocols, which tin take time and energy. Nonetheless, importing the data into Python frees the user of center-men and allows the data to be processed in whatsoever manner preferred. I use pySerial often, whether for recording temperature data using thermocouples, or high-frequency hall sensor measurements to monitor moving parts. This method can be used to take force per unit area measurements in the laboratory, or even tape calibration data to amend your instrumentation accuracy; the possibilities are truly countless.
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Source: https://makersportal.com/blog/2018/2/25/python-datalogger-reading-the-serial-output-from-arduino-to-analyze-data-using-pyserial
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