To read single byte from serial device. Data = ser.read to read given number of bytes from the serial device. Data = ser.read(size=5) to read one line from serial device. Data = ser.readline to read the data from serial device while something is being written over it. Code for python: import serial ser = serial.Serial('COM3', 9600, timeout=0) while 1: var = rawinput('Enter 0 or 1 to control led: ') ser.write(var) Reading data from sensor and printing that to computer. In this code we are going to use unknown light sensor for arduino.
In this tutorial we will see how to use the serial port on Raspberry Pi. We will use the serial port available on Raspberry with a RS232/TTL 3-5,5V adapter and a USB-serial adapter. By default the Raspberry Pi’s serial port is configured to be used for console input/output. This can help to fix problems during boot, or to log in to the Pi if the video and network are not available.
To be able to use the serial port to connect and talk to other devices (e.g. a modem a printer.. ), the serial port console login needs to be disabled.
Here we use Raspberry Pi 2, and we connect a RS232/TTL 3-5,5V adapter to pins 4 (5V), 6 (GND) ,8 (TX),10 (RX) of Raspberry, obviously connect tx with rx and vice versa.
To search for available serial ports we use the command
The output is something like this
Last line indicates that the console is enabled on the serial port ttyAMA0, so we disable it
Run the configuration command and follow the instructions below
Reboot and try with
output now is
Now we can use the serial ttyAMA0. We connect an adapter usb / serial, then we will try to establish a communication between the two serial ports; obviously in a practical application to every serial we could connect a device, for example a modem, a printer a RFID reader etc.
After connecting the second serial port we launch the command to find the name that Raspberry gives him
The output is something like this
Ok, now we create two files, one who writes something on the ttyAMA0 port and the other that reads on the ttyUSB0 port.
serial_write.py
serial_read.py
If we run both files, serial_read.py will read what serial_write.py writes
This is just a small example but it can serve as a starting point to send a print to an old printer or read data from a router or a gps.
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I'm not sure about how to properly handle timing readings from serial inside a Python script. I need to read a value every 5 seconds.
From Arduino I could do,
Inside Python script I could do,
EDIT: Apart from that, the first reading is always wrong, like if there was something in the reading buffer.I've found out that to solve that I should add
arduino.flushInput()
just after opening the port.whitenoisedb
whitenoisedbwhitenoisedb
1 Answer
The answer is that it depends on what you are actually trying to accomplish. If there is nothing else to be done on the Arduino then it is fine to have it sit and wait; on the other hand if there is nothing else for the python script to do then it is fine for it to sit and wait, but there is no reason for both of them wait.
Arduino delay
s
You don't need to deal with the timing delay in python if the Arduino is
delay
ing. According to the documentationreadline
will wait until it has received a value or until the timeout is reached. That said, I would make the timeout slightly longer than the delay on the Arduino side of things.Note that
readline
will block your program from doing anything else while it waits. As such, It is pretty useful to explore python threading
when you are writing a program which collects data over a serial stream unless the program is only collecting data. Python sleep
s
If there is other stuff to be done on the Arduino (perhaps if you are doing some filtering of the temperature data using the Arduino so as to reduce noise) then it might make more sense for it to push data to the serial stream at the end of each
loop
, and for the python script to only read the data every 5 seconds. In this case you could have python sleep
and use no delay (or a shorter delay) on the Arduino. You can achieve this behavior without resorting to using sleep
by using a timer
object to periodically call a function that open
s the serial stream (possibly flush it), reads the data, processes it, and closes the serial stream. ThismattersThismatters