I am doing a serial communication in python between a RPi and a camera. I send some data from the RPi using ser.write() and read data from the camera in the RPi using ser.read(). Then I would like to know what would ser.flush(), ser.flushinput() and ser.flushoutput() do if I add these after the read command.
I assume ser.flush() will make the program wait till all data from buffer memory is read. But I don't understand what the other two will do
Can someone tell me, what is the difference between these three when used in serial communication and what will happen when I use each of them separately after the ser.write() or ser.read().
Related
I am using PYSerial to read a Arduino which outputting data through serial to a Raspberry PI. On the PI, I'm running Python script that reads the data using pyserial. I want to run another python scripts that also reads the the same data on the same serial. Would they interfere with each other? I've tested and both scripts seam to read data and it does not crash or lock the port but wondered if problems would occurs? Both scripts perform different functions and I want to keep them separate. Both scripts start with the following code and then do something different when it gets to ##do something##
import serial
ser = serial.Serial('/dev/ttyACM1', 115200) # just change the port number to the appropriate
while True :
line = ser.readline().decode("utf-8").rstrip()
##do something##
If two scripts read exactly the same data on the serial port, then the second one will have nothing to read, because after reading a byte, it is removed from the RX buffer.
My issue is to make a serial communication between raspberry pi and another hardware. The recommended connection for this hardware is as shown on the manual, I have to connect, RX, TX, GND, RS, and CS.
But on raspberry pi we have only RX, TX so I connected RX and TX and The GNG of Pi to this hardware.
I modified Pi's parameters as shown on the link : here
Then I maked a simple python program that initialize the communication, and send data.
Here is the code :
import serial,os
port=serial.Serial("/dev/ttyAMA0",baudrate=9600)
print ('port is ok')
port.write('Command')
rcv=port.read(10)
print rcv
after running this code on pi, I got ('port is ok'), But the problem is that this hardware don't respond correctly to the command, and as respoce it gave me normally OK, but I got some extra caracter( non readable).
Is that a problem of encoding? Can some one help about this?
You need to check the baud rate on the other hardware
or make sure that the length of the received message = to the printed message.
In a serial communication, there are two important things to be careful :
The two devices have to work with the same baudrate IF the link is bidirectional.
When writing data on serial, you have to flush data just after the write().
refer to here for it.
In a lot of case, flush isn't needed, but when two different devices have to communicate, it could unlock the comm'.
If it's not efficient, try to set up your other device with the same conf (no flow control, etc)
I want to transmit AVR or Arduino etc by I2C from Raspberry pi.
I am writing in Python.
I already successeded communication using write_data() function in smbus module.
But I want to transmit multiple bytes data consecutively.
Please tell me how to transmit multiple bytes data in i2c communication.
I find write_block_data() function, but I don't understand the second parameter CMD.
What is the CMD?? Should I specify the value of CMD?
thank you.
Communicating between an RPi and an Arduino on I2C is a big mess if you are using Wire.h library. The short answer is that RPi is using a repetitive start signal while Arduino is not using it.
Repetitive start signal on I2C interface tells the slave to start answering for the call. In case of the Arduino asking and answering is in two separated calls. Therefore you cannot send block
I made two blog posts to interface the two architecture through I2C. First one is for using a remote controller PWM: http://distantorion.com/2014/10/24/rc-signals-pwm-to-i2c-with-arduino/
The second one is for driving a 128x64 LCD display on I2C: http://distantorion.com/2014/11/01/i2c-display-with-arduino/
In the second one I'm using block data in python:
bus.write_i2c_block_data(0x05,0x10,buff)
0x05 is the device address, 0x10 is the "command", buff containd the characters to display.
Regarding the commands. In I2C a slave works in a way of commands or registers. Both method looks like the same. If you are using a repetitive start signal the communication seems to be reading and writing registers. When you have no repetitive start signal, the communication looks like a command - answer system. In my example I'm sending 0x10 what is "put the characters from to the display". And 0x01 is a clear screen command, while 0x02 turns on the backlight.
Say I have the following python script to read in serial data from my Arduino:
import serial
ser = serial.Serial("dev/ttyACM1", 9600)
ser.timeout = 2
ser.readlines()
On the other end I've flashed my Arduino with a program that sends 20 voltage readings every 0.5 seconds. The Arduino starts sending those readings from the moment it's hooked up, then after 20 seconds it stops and sends nothing.
Now what I've noticed is that I can read those 20 voltage values using the first script whenever I want. That is, I can hook up the Arduino, wait a couple of minutes then read in the values. This makes me think that the data is getting stored somewhere. I'm inclined to think that it's not being stored on the Arduino but on my laptop somewhere.
I've come up with a few questions that I hope the community could help me with:
Where is PySerial getting the data from (the Arduino or some buffer on my laptop)?
For how long is the data stored in this place?
Is there a way to clear this space before reading in values?
How much storage space is there?
When you set the baud rate in PySerial (second line in script), is this the rate that
PySerial reads data from the storage area (not the Arduino)?
I've noticed that if I set the baud rate in PySerial too high the first few lines of data are fragmented and sometimes completely wrong, why?
Not exactly related but when you set serial.Serial.timeout are the
units in seconds?
I appreciate your time.
Have you tried using a terminal program like TerraTerm (windows) or GTKTerm (linux) to open the same port to the arduino? I think this would be helpful to answer some of your questions.
Some quick answers to your questions that I can dump off the top of my head.
From the port specified, I'm guessing you are asking something deeper than this?
If you do a
x = ser.readlines()
then the data will be in x as long as you'd like.
There is a flush function defined in PySerial
Not sure. You can specify how many characters you would like to read though
example:
x = ser.read(number)
The pyserial documentation states the following
Read size bytes from the serial port. If a timeout is set it may return less characters as requested. With no timeout it will block until the requested number of bytes is read.
http://pyserial.sourceforge.net/pyserial_api.html
This is the clock rate of the port you are opening, ie /dev/ttyACM1, most serial comms are at 9600, if you happen to be using a USB to serial you'll need 115200
Clock rate mismatch. You're computer is sampling data at a rate higher than the arduino is providing it, causing it to be incorrectly displayed.
Seconds, quote from Pyserial documentation : "timeout = x: set timeout to x seconds (float allowed)" Same link as number 4
Hope that helps some!
All right, so I am positive my Arduino circuit is correct and the code for it. I know this because when I use the serial monitor built into the Arduino IDE and send 'H' an LED lights up, when I send 'L' that LED turns off.
Now I made a Python program
import serial
ser = serial.Serial("COM4",9600)
ser.write("H")
When I run the code the LED blinks on for a second then goes back off.
However when I do each of these lines separately in the shell it works just like it is supposed to.
Any ideas?
When you open the serial port, this causes the Arduino to reset. Since the Arduino takes some time to bootup, all the input goes to the bitbucket (or probably to the bootloader which does god knows what with it). If you insert a sleep, you wait for the Arduino to come up so your serial code. This is why it works interactively; you were waiting the 1.5 seconds needed for the software to come up.
I confirmed that opening the serial port resets my Arduino Uno; I flashed a program which will blink the LED from the setup() routine -- calling open("/dev/ttyACM0") was sufficient to trigger the reset. This is IMHO a confusing and undocumented wrinkle in the serial support.
I had the same problem and it works if I add a delay of about 2 seconds from opening the serial connection to writing on it, 1 second was not enough.
Just to make it a bit more clear I'll modify the code so everyone can see what needs to be added!
import serial
import time
ser = serial.Serial("COM4",9600)
time.sleep(3)
ser.write("H")
Adding in a sleep statment helps to let the serial open up without any problems!
Assuming you are using an Arduino Uno
The USB port and the Uno serial bus exposed on pins 1 and 0 share the same RX/TX lines. I suggest getting a USB to TTL adapter like the one here so that you can communicate to the Arduino without using the USB port. The Arduino IDE has its own method for disengaging from the USB driver such that a virtual serial port can be created. Have your Ardunio use SoftwareSerial instead.
Here is an example I found on the internet where somebody had clashing bus issues.