I'm building an embedded device with a couple of sensors. The device will 'stream' digital data from these sensors over Bluetooth or USB.
Most of the communication will be from the embedded device to the host. The host will infrequently be sending control messages, to control the gain etc.
Since the physical and data link layers are taken care of, I'm looking for a simple message protocol that will make it easy to develop user applications to process/display data on the host computer. Does anyone have any suggestions?
A simple text protocol may be the best for this application.
Use the communication channel as a bi-directional serial pipe.
The device can stream sensor values in ASCII (text) format, separated by commas, with each set separated by the newline character. The rate is preferably set by the host.
For example,
21204,32014 (new line character '\n' - 0x0A) at the end of each line
21203,32014
21202,32011
....
This makes it easier to test, to stream the values to a file, import in to a spreadsheet etc.
Similarly commands to the device too, is best done in text.
SET GAIN_1 2 ( sent by host )
OK ( reply by device )
SET GAIN_2 4 (sent by host )
OK ( reply by device )
SET GAIN_9 2 (sent by host )
ERROR ( reply by device if it does not understand)
SET RATE 500 ( set the sensor dump rate to every 500 ms )
OK
Related
I have been trying to inject raw UBX data which I gather from UBXReader library into my Pixhawk. For this, I use a GPS module to extract UBX data and a serial to USB converter to stream data into my Pixhawk. Here is what my setup looks like:
Using my other USB port, I gather GPS data and try to stream it into pixhawk as seen above. For this task, I use python.
from serial import Serial
from pyubx2 import UBXReader
stream = Serial('/dev/ttyUSB0', 38400, timeout=3)
stream2 = Serial('/dev/ttyUSB1', 38400, timeout=3)
while 1:
ubr = UBXReader(stream)
(raw_data, parsed_data) = ubr.read()
output = parsed_data.serialize()
stream2.write(output)
From MAVLink, I can see location and altitude data but I fail to stream HDOP and VDOP messages into my Pixhawk. What might be causing this and how should I proceed on fixing it?
You need to ensure your external GPS is outputting the requisite UBX message types - not all UBX messages contain hDOP or vDOP data. For example:
The NAV-PVT message contains lat, lon and pDOP but not vDOP or hDOP.
The NAV-DOP message contains hDOP and vDOP but not lat or lon.
So you may need to enable the NAV-DOP message on your external GPS using uCenter or PyGPSClient.
I am trying to establish a bluetooth serial communication link between a Raspberry Pi Zero W, running Raspbian Jessie [03-07-2017], and an Arduino (UNO).
I am currently able to write data to the Arduino using bluetoothctl.
The application requires that we are able to write data to a particular BLE Slave. There are multiple [HM-10] Slaves to switch between, the Slave needs to be chosen during the program execution.
There is no BAUD rate preference. Currently, we are using 9600 universally.
Functions have been created that automatically connect and then write data to an "attribute", this shows up as data on the Serial Monitor of the Arduino.
Python Code - using BlueZ 5.44 (manually installed):
import subprocess
from subprocess import Popen, PIPE
# Replaces the ':' with '_' to allow the MacAddress to be in the form
# of a "Path" when "selecting an attribute"
def changeMacAddr(word):
return ''.join(c if c != ':' else '_' for c in word)
# Connects to a given MacAddress and then selects the attribute to write to
def connBT(BTsubProcess, stringMacAddr):
BTsubProcess.stdin.write(bytes("".join("connect "+stringMacAddr +"\n"), "utf-8"))
BTsubProcess.stdin.flush()
time.sleep(2)
stringFormat = changeMacAddr(stringMacAddr)
BTsubProcess.stdin.write(bytes("".join("select-attribute /org/bluez/hci0/dev_"
+ stringFormat +
"/service0010/char0011" + "\n"), "utf-8"))
BTsubProcess.stdin.flush()
# Can only be run once connBT has run - writes the data in a list [must have numbers 0 - 255 ]
def writeBT(BTsubProcess, listOfData):
stringList = [str('{0} ').format(elem) for elem in listOfData]
BTsubProcess.stdin.write(bytes("".join("write " + "".join(stringList) + "\n"), "utf-8"))
BTsubProcess.stdin.flush()
# Disconnects
def clostBT(BTsubProcess):
BTsubProcess.communicate(bytes("disconnect\n", "utf-8"))
# To use the functions a subprocess "instance" of bluetoothctl must be made
blt = subprocess.Popen(["bluetoothctl"], stdin=subprocess.PIPE, shell=True)
# blt with then be passed into the function for BTsubProcess
# Note: the MacAddresses of the Bluetooth modules were pre-connected and trusted manually via bluetoothctl
This method works fine for small sets of data, but my requirements require me to stream data to the Arduino very quickly.
The current set up is:
Sensor data (accelerometer, EEG) via USB serial is received by the Pi
The Pi processes the data
Commands are then sent to the Arduino via the in built bluetooth of the Pi Zero W
However, while using this method the bluetooth data transmission would delay (temporarily freeze) when the sensor data changed.
The data transmission was flawless when using two pre-paired HM-10 modules, the Pi's GPIO serial port was configured using PySerial.
The following methods have also been tried:
Using WiringPi to set-up a bluetooth serial port on the /dev/ttyAMA0
using Python sockets and rfcomm
When attempting to use both of these methods. The Python code compiles, however, once the Serial Port is opened the data is seemingly not written and does not show up on the Arduino's Serial Monitor.
This then cripples the previous functions. Even when using bluetoothctl manually, the module cannot be unpaired/disconnected. Writing to the appropriate attribute does not work either.
A restart is required to regain normal function.
Is this approach correct?
Is there a better way to send data over BLE?
UPDATE: 05/07/2017
I am no longer working on this project. But troubleshooting has led me to believe that a "race condition" in the code may have led to the program not functioning as intended.
This was verified during the testing phase where a more barebones code was created that functioned very well.
I have two similar modems, when I insert the SIM in the first modem it connects automatically to the network. But if I insert the same SIM in the second modem, it doesn't connect to the network.
I launched the command: AT&V to read the profile of each modem. I compared the settings and they are all the same except for the following:
+CGDCONT: (1,"IP","cmnet","0.0.0.0",0,0)
+CGDCONT: (1,"IP","internet","0.0.0.0",0,0)
----------------------
+CIND: 0,3,1,0,0,0,1,0
+CIND: 0,0,0,0,0,0,0,0
----------------------
+CGATT: 1
+CGATT: 0
----------------------
+COPS: 1,0,""
+COPS: 0,2,""
----------------------
Q1: Could one of these settings cause the problem?
Q2: Is there a way to save/restore a modem config?
NB. The first setting of each pair is of the working modem.
Looks like the APN of the second modem is different from the first one. The APN of second modem is "internet", while the first one is "cmnet". This can cause the problem (first one is attached while the second one did not: +CGATT 1 vs 0), if the network does not support "internet" APN.
You can set same APN for the second modem as the first one to have a try. i.e.
AT+CGDCONT =1,"IP","cmnet"
But, APN difference is only one of the possible reasons. For analyzing the actual reason of attach failure, logs are needed.
I am trying to find any element refer to IncomingBitrate in webrtc dump file .
Where I can find the incoming bitrate in webrtc-internals?
Also, How I can calculate incoming bitrate from webrtc stats?
In webrtc-internals check the active connection -- it's printed in bold. Usually it is Conn-Audio-1-0. There are two fields bytesSent and bytesReceived which will allow you to calculate the bitrate. Also check the constraints + stats demo for an actual example: https://webrtc.github.io/samples/src/content/peerconnection/constraints/
In getStats, iterate the reports until you find one of kind googCandidatePair with .stat('googActiveConnection') === 'true'. That is giving you the same information as webrtc-internals. If you want per-track/stream values, reports of type ssrc have bytesSent or bytesReceived, depending on whether they are sent or received.
Then calculate the bitrate by dividing the bytes sent/received by the time difference between the getStats calls.
I have a VW Golf 4, which is quite old and talks KWP 2000 (ISO 9141) on its CAN bus. I use a dongle powered by ELM 327, connected to the OBD-2 port of the car.
I am trying to send messages individually to each ECU. I tried to change the header of the messages:
AT SH 48 XX F1 (I hoped XX would be the ECU ID; 48 is the flag for "use physical addressing"). Any command I issue (e.g. tried 3E for "tester present") returns NO DATA (I disabled automatic timeouts and set the timeout to maximum value).
Is there a way to send messages directly to the ECU? I am not interested in the set of data provided via OBD-2, neither do I want to re-flash the ECUs. At the moment I just try to find out which ECUs are available on the bus.
Thanks!
VW works on Transport Protocol TP 2.0, hence you need to initialize with 0x200 header.
https://jazdw.net/tp20
See above link for more info.