Develop Reference

Using serial ports over bluetooth with micro bit

I have correctly got a microbit working with serial communication via COM port USB.
My aim is to use COM over bluetooth to do the same.
Steps I have taken:
(on windows 10) bluetooth settings -> more bluetooth settings -> COM ports -> add -> incoming
in device manager changed the baud rate to match that of the microbit (115,200)
paired and connected to the microbit
tried to write to both the serial and uart bluetooth connection from the microbit to the PC (using a flashed python script)
using Tera Term, setup -> serial port... -> COM(number - in my case 4), with all necessary values (including 115,200 baud rate)
After doing all of these, I see no incoming message on Tera Term. Have I missed anything?

This is not directly possible via BLE UART communication because it uses different protocols (as mentioned above by ukBaz).
You are able to, however, communicate via custom BLE libraries such as bleak.
Bleak has some good examples on its github repo of how to scan GATT characteristics and services to find the TX and RX characteristics of your BLE device.
From there you're able to connect to the microbit directly over bluetooth and read and write to it's GATT table and not using the proprietary BLE protocols etc.
I'll make a tutorial at some point and link it back here when it's done.

python communication MODBUS TCP/IP raspberry pi and HMI - write value

I'm French student and i need your help in Python for my program.
I've got a program in my rapsberry in Python which acquire datas from temperature and hygrometry sensors.
I need to communicate these values to an Human Machine Interface supervisor by the MODBUS TCP/IP PROTOCOL to display and made some graphics of these values in my HMI
The IP adress of the raspberry : 172.16.0.2
The IP adress of the HMI : 172.16.0.10
I think I need to use package like pyModbusTCP or things like that but I don't understand how to use it.
Could you help me to understand how I made the communication between my Rpi and my HMI and for example how I could write the integer value 100 at the address index 1?
Thanks for all!
Antoine

MODBUS is a single-master protocol, meaning that there can only be one master, the rest of attached devices are slaves ( http://www.ni.com/white-paper/52134/en/ , similar to USB protocol, called host and device there ). In addition in MODBUS protocol a slave never starts a communications, slaves only answer to requests. Consequentially the machine on that your HMI runs has to be the MODBUS master /client ( this naming convention is a bit senseless )
For a quick general overview read this https://www.reddit.com/r/PLC/comments/7bqppu/using_raspberry_pi_as_modbus_slave_and/ and http://www.simplymodbus.ca/TCP.htm
pymodbus client / master on HMI machine
From this master / client you can send requests to the RPi ( MODBUS slave / server ) with its sensors using the following code ( if one of the sensors stores its data in a register that is presented to the bus as coil 1 by the pymodbus server that runs on the RPi, see below ). This is only an example there are other data blocks in MODBUS, namely Coils, Discrete Inputs, Input Registers, Holding Registers which of them you use depends on how you configure the MODBUS server on the RPi, normally Discrete Inputs and Input Registers are rarely used :
client = ModbusTcpClient('172.16.0.2')
client.write_coil(1, True)
result = client.read_coils(1,1)
print(result.bits[0])
client.close()
https://github.com/riptideio/pymodbus
pymodbus server / slave on Rpi
For this to work on the RPi has to run software ( pymodbus server ) that enables it as MODBUS slave / server and the sensors have to write their values into specific memory locations that are presented to MODBUS as coils / registers. How this can be done is in https://www.youtube.com/watch?v=p3Dgd0PDjnU and https://jacekhryniewicz.wixsite.com/website/raspberry-pi-with-modbus-tcp ( is a bit outdated )
In https://github.com/riptideio/pymodbus/blob/master/examples/common/asynchronous_server.py is a working example of a MODBUS server that has to run onthe RPi ( read the comments, especially the lines following # initialize your data store )
The word coils has its origin in the past of MODBUS protocol which was developed when electromechanical relays with coils were used in automation technology

Facing problems with socket programming for video streaming

I have two transceivers which support serial communication (UART). I am using socket programming on python for generating UDP data grams. Is there any way to port these datagrams to the serial port on the transmitter and then back from serial port to UDP datagram on the receiver. I am new to this so some examples would be highly appreciated.

Use the point-to-point protocol (PPP). That's what it was designed to do.
If you're running on Linux or some other UNIX-like operating system, you'll use pppd on both ends of the serial connection.
Most of the articles on setting this kind of thing up date back to the dial-up internet days. Here's an example: http://www.tldp.org/HOWTO/PPP-HOWTO/
Essentially, PPP creates interfaces with IP addresses on both ends of your serial connection. Send packets to the remote interface's IP address, and it tunnels them over the serial link.

Use UDP without specifc port for Multicast

IP multicast gives you the ability to send a single packet, which is picked up by multiple interfaces if they are subscribed to that multicast. If I understand it correctly.
Now if I want to use UDP, in combination with IP multicast, I am obligated to assign a port to listen to. But now I understand that I only receive UDP packets on a multicast specifically sent to that port. But I would like to intercept all UDP packets send to a certain multicast IP address, regardless of the port and receive them at my single socket.
Is something like this possible?
Preferably accompanied by a python example, if this is possible.

This isn't possible using the BSD socket API (which is roughly the API Python exposes in its socket module) - except by creating 2 ** 16 - 1 sockets and using them to bind to all ports.
It's possible using lower-level interfaces such as the TUN/TAP system offered by Linux.

Pymodbus (Serial) over a tcp serial connection

I will be creating a connection between my Linux server and a cellular modem where the modem will act as a server for serial over TCP.
The modem itself is connected to a modbus device (industrial protocol) via an RS232 connection.
I would like to use pymodbus to facilitate talking to the end modbus device. However, I cannot use the TCP modbus option in PyModbus as the end device speaks serial modbus (Modbus RTU). And I cannot use the serial modbus option in Pymodbus as it expects to open an actual local serial port (tty device) on the linux server.
How can I bridge the serial connection such that the pymodbus library will see the connection as a local serial device?

There is no straightforward solution to trick your linux server into thinking that a MODBUS RTU is actually of MODBUS TCP connection.
In all cases, your modem will have to transfer data from TCP to serial (and the other way around). So I assume that:
1) somehow you can program your modem and instruct it to do whatever you want
2) the manufacturer of the modem has provided a built-in mechanism to do that.
If 1): you should program your modem so that it can replace TCP ADUs by RTU ADUs (and the other way around) when copying data from the TCP connection to the RS link.
If 2): simply provide your RTU frame to whatever API the manufacturer devised.

I actually was working on something similar and decided to make my own Serial/TCP bridge. Using virtual serial ports to handle the communication with each of the modems.
I used the minimalmodbus library although I had to modify it a little in order to handle the virtual serial ports.
I hope you solved your problem and if you didn't I can try to help you out.