Very easy to run. All PIs should be on the same network.
1) Extract Zip on Desktop
2) Open terminal (you can easily press Tools -> Open Current Folder in terminal)
3) type: python server.py
4)In the extracted folder there’s a text file called ‘url.txt’. Open it and share the hyperlink with your audience
Let’s say that you have a running Flask server and you want your user to control the state (on/off) of an LED via the GPIO. The following technique shows how to connect Flask server with a separate GPIO script using PID.
Run the following two scripts at the same time using the terminal:
from flask import *
import os
import signal
app = Flask(__name__)
#create a route path for index page
@app.route("/")
def index():
return render_template("index.html")
#create a route path for about page
@app.route("/about")
def about():
if 'name' in session: #if session 'name' exists
print(session['name']) #print what's inside session[name]
session.pop('name',None) #after printing, delete session name
return render_template("aboutus.html") #render the html template aboutus
#/students accepts a get and post requests
@app.route("/student",methods=['GET','POST'])
def student():
if(request.method == 'POST'): #if user fills a form
studentName = request.form['studentname']
if(studentName == "jimmy"):
session["name"] = studentName #create session, name it 'name' and fill with studentName
return redirect(url_for("about")) #redirect to about page
else:
return render_template("student.html") #render student template
else:
return render_template("student.html")#render student template
#routes with paramaters
@app.route("/led")
@app.route("/led/<param>")
def led(param=None):
if(param == "on"): #if paramater is /led/on
#read process id from text file generated by ledscript.py
fh=open("processid.txt","r")
processId = int(fh.read()) #load the process id
fh.close()
fh=open("led.txt","w")
fh.write("1") #save 1 in text file. 1 means LED ON. 0 means LED Off
fh.close()
#send signal to process id
os.kill(processId, signal.SIGUSR1)
return "LED ON"
elif(param =="off"): # if paramater is /led/off
#read process id from text file
fh=open("processid.txt","r")
processId = int(fh.read())
fh.close()
fh=open("led.txt","w")
fh.write("0")
fh.close()
#send signal to process id (ledscript)
os.kill(processId, signal.SIGUSR1)
return "LED OFF"
else:
return "LED MAIN PAGE"
if __name__ == "__main__":
app.secret_key = 'asdfd!45sdf' #create secret key to secure sessions
app.run(debug=True, host = "0.0.0.0")
import RPi.GPIO as GPIO
import time
import traceback
import os
import signal
def Main():
try:
#when scripts runs create processid.txt
fh=open("processid.txt","w")
fh.write(str(os.getpid())) #get current process id and store in file
fh.close()
GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
GPIO.setup(4, GPIO.OUT, initial = GPIO.LOW) #setup GPIO4 to low
def handUSR1(signum,frame): #this function is automatically triggered from flask
fh=open("led.txt","r")
led = int(fh.read())
fh.close()
if(led == 0): #if 0 is found in text file
print("LED OFF") #turn off led
GPIO.output(4,GPIO.LOW)
else:
print("LED ON") #if not 0 (1) is found in text file
GPIO.output(4,GPIO.HIGH) #turn on led
signal.signal(signal.SIGUSR1,handUSR1) #callback function for SIGUSR1 signal (from flask when kill command is given)
while(True):
time.sleep(1)
except Exception as ex:
traceback.print_exc()
finally:
GPIO.cleanup() #this ensures a clean exit
Main()
Let’s say that you have a running Flask server and you want your user to control the state (on/off) of a motion sensor via the GPIO. The most complex way is to create a multi-threading script which handles the server and GPIO code.
Another approach is to separate the server script from the GPIO script. Thus having two layers of scripts. This has the advantage to debug in isolation. For this technique one has to use Unix Signals which can be used to send signals from one process to another.
When you execute a script on your UNIX system, the system creates a process id (pid) which is different every time. A signal is a software interrupt which notifies a process with a significant event or request.
The following table gives a list of the most common signals:
| NAME | NUMBER | DESCRIPTION |
| SIGHUP | 1 | Linux sends a process this signal when it becomes disconnected from a terminal. |
| SIGINT | 2 | Linux sends a process this signal when the user tries to end it by
pressing CTRL+C. |
| SIGILL | 4 | Linux sends a process this signal when it attempts to execute an illegal instruction. |
| SIGABRT | 6 | Linux sends a process this signal to the process when the process calls the ‘abort ()’ function |
| SIGFPE | 8 | Linux sends a process this signal when it has executed an invalid floating-point math instruction |
| SIGKILL | 9 | Linux sends a process this signal to end it immediately |
| SIGUSR1 | 10 | User programs can send this signal to other process |
| SIGUSR2 | 12 | User programs can send this signal to other process |
| SIGSEGV | 11 | Linux sends a process this signal when the program has attempted an invalid memory access |
| SIGPIPE | 13 | Linux sends a process this signal when the program has attempted to access a broken data stream, such as a socket connection that has been already closed |
| SIGALRM | 14 | A process can receive this signal from the Linux using the function alarm (), after a time period mentioned in its argument. |
| SIGTERM | 15 | Linux sends a process this signal requesting it to terminate |
| SIGCHLD | 17 | Linux sends a process this signal when a child process exits |
| SIGXCPU | 24 | Linux sends a process this signal when it exceeds the limit of
CPU time that it can consume. |
| SIGVTALRM | 26 | A process can receive this signal from the Linux using the function setitimer (), after a time period mentioned in its argument. |
We are interested in SIGUSR1 and SIGUSR2 which can be used to send user signals.
Step 1:
First create the server layer (app.py). Documentation about Flask server can be found here.
from flask import *
import os
import signal
app = Flask(__name__)
@app.route('/')
def index():
return render_template('index.html')
@app.route('/trigger1')
def process1():
#read process id from text file
fh=open("processid.txt","r")
processId = int(fh.read())
fh.close()
#send signal to process id
os.kill(processId, signal.SIGUSR1)
return render_template('trigger1.html')
@app.route('/trigger2')
def process2():
#read process id from text file
fh=open("processid.txt","r")
processId = int(fh.read())
fh.close()
#send signal to process id
os.kill(processId, signal.SIGUSR2)
return render_template('trigger2.html')
if __name__ == '__main__':
app.run(debug=True,host='0.0.0.0')
Step 2:
Create the SignalReceiver.py script (you can modify this to control the GPIOs)
import os
import signal
import time
fh=open("processid.txt","w")
fh.write(str(os.getpid())) #get current process id and store in file
fh.close()
def handUSR1(signum,frame):
print('triggered',signum)
def handUSR2(signum,frame):
print('triggered',signum)
signal.signal(signal.SIGUSR1,handUSR1) #callback function for SIGUSR1 signal
signal.signal(signal.SIGUSR2,handUSR2) #callback function for SIGUSR2 signal
while(True):
time.sleep(1)
print("Waiting for signal")
Step 3: Run Server
Step 4: Run SignalReceiver.py
Step 5:
In the browser, click Trigger 1 and Trigger 2 hyperlink buttons. Notice that SignalReceiver.py outputs ‘triggered 10′ and ‘triggered 12′. This means that both signals were sent and received correctly.
Link to project: https://sourceforge.net/projects/pi-send-signals-to-scripts/
Please note that this is not officially approved by the PI team but the MagPi magazine offers a similar tutorial using a pendrive.
Step 1
Download the Pixel (Jessie Raspbian) image file: http://downloads.raspberrypi.org/pixel_x86/images/pixel_x86-2016-12-13/2016-12-13-pixel-x86-jessie.iso
Step 2:
Open Virtual Box, press new and create the following settings:
Press Create and enter the following settings
Press Start
Step 3:
Browse to the downloaded ISO file and press Start
Pixel is loaded
Step 4:
To test persistence, create a new folder on your desktop and restart your OS.
Once your OS is restarted, you will notice that the folder you created is lost. This is because there is no persistence drive present.
Step 5 (to create persistence drive):
Open terminal window and enter sudo apt install gparted
When installation is finished, enter sudo gparted
Click on Device > Create Partition Table and press Apply
Right Click on the unallocated partition and press New
Enter label name persistence with the following default settings and press Add
Press the green very good sign and press Apply to any warning messages
Press Close and close everything
Now we are going to copy the whole operating system from the virtual optical drive to
the hard drive.
Open the terminal window and enter sudo dd if=/dev/sr0 of=/dev/sda bs=1M
Close the virtual machine (shutdown the OS)
Step 6:
Create a new Virtual Machine with the following settings. It is very important that you use your previously created virtual hard disk file. Do no create a new virtual hard disk.
Step 7:
Start your new machine and create a new python script to test persistence. I saved my file in the desktop. Restart your OS.
Step 8:
Test file is still there. Persistence worked 🙂
References:
Download my new Android App – Screen Sky
– This app changes your wallpaper automatically every 60 minutes according to the weather. Weather data is collected from openweathermap.org by using your GPS location.
– You can also upload your pictures or take photos and tag them with weather and time conditions.
– Default app pictures and uploaded photos can be deleted by a long click on the respective image.
– Notifications are pushed when no wallpapers are found under respective weather and time status.
So here’s the story:
sudo apt-get install mpd mpc
| Classic FM | mpc add http://media-ice.musicradio.com/ClassicFMMP3 |
| Radio Malta 1 | mpc add http://s38.myradiostream.com:6982 |
| One Radio | mpc add http://162.252.85.85:8202/stream/1/ |
| Radio Malta 2 | mpc add http://s11.myradiostream.com:4954 |
| Magic Malta | mpc add http://s46.myradiostream.com:6076 |
| Radio 101 | mpc add http://stream.vanilla.net.mt:8000/Title1=Radio%20101Length1=-1Version=2 |
| Radju Marija | mpc add http://dreamsiteradiocp2.com:8096 |
| bay radio | mpc add http://s1.voscast.com:8132 |
| bay easy | mpc add http://s1.voscast.com:8154 |
| bay retro | mpc add http://s1.voscast.com:8156 |
| Campus FM | mpc add mms://stream.um.edu.mt/CampusFM |
| RTK FM | mpc add http://stardust.wavestreamer.com:3328/Live |
| Vibe FM | mpc add http://s9.voscast.com:7824/ |
| Bkara FM | mpc add http://majestic.wavestreamer.com:8209/Live |
#!/usr/bin/python
# Example using a character LCD plate.
import time
import Adafruit_CharLCD as LCD
import traceback
import subprocess
import os.path
import os
# Initialize the LCD using the pins
lcd = LCD.Adafruit_CharLCDPlate()
# create some custom characters
lcd.create_char(1, [2, 3, 2, 2, 14, 30, 12, 0])
lcd.create_char(2, [0, 1, 3, 22, 28, 8, 0, 0])
lcd.create_char(3, [0, 14, 21, 23, 17, 14, 0, 0])
lcd.create_char(4, [31, 17, 10, 4, 10, 17, 31, 0])
lcd.create_char(5, [8, 12, 10, 9, 10, 12, 8, 0])
lcd.create_char(6, [2, 6, 10, 18, 10, 6, 2, 0])
lcd.create_char(7, [31, 17, 21, 21, 21, 21, 17, 31])
#turn on green light
lcd.set_color(0.0, 0.0, 1.0)
lcd.clear()
lcd.message("connecting: \n")
message = ""
def isConnected():
global lcd
while True: #keep repeating until internet connection is found
try:
ip = subprocess.check_output("hostname -I",shell=True)
ip = ip[:3]
if ip != "192":
counter = 0
while True:
print 'trying to connect to internet'
lcd.clear()
lcd.message("connecting to\n internet")
time.sleep(1)
remote_server = "8.8.8.8"
status = subprocess.call(['ping','-c','1',remote_server])#test connection with google
if(status == 0):
lcd.clear()
startPlaying()
break
else:
counter +=1
if(counter > 3):
break
else:
break
except:
pass
def startPlaying():
global lcd
lcd.clear()
subprocess.call("mpc stop ",shell=True)
subprocess.call("mpc play ",shell=True) #start player
updateCurrentStation()
lcd.clear()
def updateCurrentStation():
global message
time.sleep(0.2)
message = subprocess.check_output('mpc current',shell=True)
message = updateStationName(message.strip())
if(len(message) > 15):
message = message[:16] + '\n' + message[16:30]
def updateStationName(message): #this function updates those station name that are not returning a proper name
if(message == "http://stream.vanilla.net.mt:8000/Title1=Radio%20101Length1=-1Version=2"):
message = "101"
elif(message == "http://162.252.85.85:8202/stream/1/"):
message = "One Radio"
elif(message == "http://majestic.wavestreamer.com:8209/Live"):
message = "Bkara FM"
elif(message == "http://stardust.wavestreamer.com:3328/Live"):
message = "RTK"
elif(message == "http://media-ice.musicradio.com/ClassicFMMP3"):
message = "Classic FM"
return message
def checkStatus():
status = subprocess.check_output('mpc status',shell=True)
if(status[0:6] == 'volume'): #empty status starts with text volume
startPlaying()
def Main():
global lcd
global message
cache_oldmessage = ""
try:
# Make list of button value, text, and backlight color.
buttons = ( (LCD.SELECT, 'Select', (1,1,1)),
(LCD.LEFT, 'Left' , (1,0,0)),
(LCD.UP, 'Up' , (0,0,1)),
(LCD.DOWN, 'Down' , (0,1,0)),
(LCD.RIGHT, 'Right' , (1,0,1)) )
while True:
isConnected()
updateCurrentStation()
# Loop through each button and check if it is pressed.
for button in buttons:
if lcd.is_pressed(button[0]):
if(button[0] == LCD.LEFT):
print("left button")
lcd.clear()
lcd.message("connecting:\n ")
subprocess.call("mpc next ",shell=True)
checkStatus()
updateCurrentStation()
elif(button[0] == LCD.RIGHT):
print("right button")
lcd.clear()
lcd.message("connecting: \n")
subprocess.call("mpc prev ",shell=True)
checkStatus()
updateCurrentStation()
elif(button[0] == LCD.UP):
subprocess.call("mpc volume +5" ,shell=True)
print("volume increased")
elif(button[0] == LCD.DOWN):
subprocess.call("mpc volume -5" ,shell=True)
print("volume decreased")
elif(button[0] == LCD.SELECT):
lcd.set_color(0.0, 1.0, 1.0)
lcd.clear()
lcd.message('Goodbye...')
time.sleep(2.0)
lcd.clear()
lcd.set_color(0.0, 0.0, 0.0)
#subprocess.call(['poweroff -f'], shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
os.system('shutdown now -h')
time.sleep(0.75) #button click delay
if(cache_oldmessage != message):
lcd.clear()
lcd.message(message)
cache_oldmessage = message
except Exception as ex:
traceback.print_exc()
lcd.set_color(1.0, 0.0, 0.0)
lcd.clear()
lcd.message("error")
Main()
