• How socket communication works
• How to transfer data from one Raspberry Pi to another using Python 3 and TCP Networking
• How to automatically implement outputs on a distant Raspberry Pi from inputs on a local Raspberry Pi

You can copy / paste the code below if you’re having issues with typos or want a shortcut. However I recommend that you follow along in the tutorial to understand what is going on!

cookieServer.py

import socket

host = ''
port = 5560

storedValue = "Yo, what's up?"

def setupServer():
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    print("Socket created.")
    try:
        s.bind((host, port))
    except socket.error as msg:
        print(msg)
    print("Socket bind comlete.")
    return s

def setupConnection():
    s.listen(1) # Allows one connection at a time.
    conn, address = s.accept()
    print("Connected to: " + address[0] + ":" + str(address[1]))
    return conn

def GET():
    reply = storedValue
    return reply

def REPEAT(dataMessage):
    reply = dataMessage[1]
    return reply

def dataTransfer(conn):
    # A big loop that sends/receives data until told not to.
    while True:
        # Receive the data
        data = conn.recv(1024) # receive the data
        data = data.decode('utf-8')
        # Split the data such that you separate the command
        # from the rest of the data.
        dataMessage = data.split(' ', 1)
        command = dataMessage[0]
        if command == 'GET':
            reply = GET()
        elif command == 'REPEAT':
            reply = REPEAT(dataMessage)
        elif command == 'EXIT':
            print("Our client has left us :(")
            break
        elif command == 'KILL':
            print("Our server is shutting down.")
            s.close()
            break
        else:
            reply = 'Unknown Command'
        # Send the reply back to the client
        conn.sendall(str.encode(reply))
        print("Data has been sent!")
    conn.close()
        

s = setupServer()

while True:
    try:
        conn = setupConnection()
        dataTransfer(conn)
    except:
        break

cookieClient.py

import socket

host = '192.168.1.79'
port = 5560

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((host, port))

while True:
    command = input("Enter your command: ")
    if command == 'EXIT':
        # Send EXIT request to other end
        s.send(str.encode(command))
        break
    elif command == 'KILL':
        # Send KILL command
        s.send(str.encode(command))
        break
    s.send(str.encode(command))
    reply = s.recv(1024)
    print(reply.decode('utf-8'))

s.close()

cookieClient2.py

import socket
from time import sleep

host = '192.168.1.79'
port = 5560

def setupSocket():
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.connect((host, port))
    return s

def sendReceive(s, message):
    s.send(str.encode(message))
    reply = s.recv(1024)
    print("We have received a reply")
    print("Send closing message.")
    s.send(str.encode("EXIT"))
    s.close()
    reply = reply.decode('utf-8')
    return reply

def transmit(message):
    s = setupSocket()
    response = sendReceive(s, message)
    return response

cookieAnalog2.py

import spidev

# First open up SPI bus
spi = spidev.SpiDev()
spi.open(0,0)

# Initialize what sensor is where
tempChannel = 0

def getReading(channel):
    # First pull the raw data from the chip
    rawData = spi.xfer([1, (8 + channel) << 4, 0&#93;)
    # Process the raw data into something we understand.
    processedData = ((rawData&#91;1&#93;&3) << 8) + rawData&#91;2&#93;
    return processedData

def convertVoltage(bitValue, decimalPlaces=2):
    voltage = (bitValue * 3.3) / float(1023)
    voltage = round(voltage, decimalPlaces)
    return voltage

def convertTemp(bitValue, decimalPlaces=2):
    # Converts to degrees Celsius
    temperature = ((bitValue * 330)/float(1023) - 50)
    temperature = round(temperature, decimalPlaces)
    return temperature

def getTemp():
    tempData = getReading(tempChannel)
    temperature = convertTemp(tempData)
    return temperature

#>

cookieMain2.py

import P3picam
import picamera
from datetime import datetime
from subprocess import call
from time import sleep
from cookieClient2 import transmit
from cookieAnalog2 import getTemp

motionState = False
picPath = "/home/pi/Desktop/cookie/images/"
sleepTime = 3
triggerTemp = 20

def captureImage(currentTime, picPath):
    # Generate the picture's name
    picName = currentTime.strftime("%Y.%m.%d-%H%M%S") + '.jpg'
    with picamera.PiCamera() as camera:
        camera.resolution = (1280, 720)
        camera.capture(picPath + picName)
    print("We have taken a picture.")
    return picName

def getTime():
    # Fetch the current time
    currentTime = datetime.now()
    return currentTime

def timeStamp(currentTime, picPath, picName):
    # Variable for file path
    filepath = picPath + picName
    # Create message to stamp on picture
    message = currentTime.strftime("%Y.%m.%d - %H:%M:%S")
    # Create command to execute
    timestampCommand = "/usr/bin/convert " + filepath + " -pointsize 36 \
    -fill red -annotate +700+650 '" + message + "' " + filepath
    # Execute the command
    call([timestampCommand], shell=True)
    print("We have timestamped our picture.")

def tempMonitor():
    print("About to take a reading.")
    temp = float(getTemp())
    print("Out temp is: " + str(temp))
    if temp > float(triggerTemp):
        message = "LED_ON"
        print("Transmitting data.")
        response = transmit(message)
        print(response)

while True:
    #motionState = P3picam.motion()
    tempMonitor()
    sleep(sleepTime)
    #print(motionState)
    #if motionState:
    #    currentTime = getTime()
    #    picName = captureImage(currentTime, picPath)
    #    timeStamp(currentTime, picPath, picName)
        

cookieLED.py

import RPi.GPIO as GPIO
from time import sleep

sleepTime = 5
ledPin = 12

def ledSetup():
    GPIO.setmode(GPIO.BOARD)
    GPIO.setup(ledPin, GPIO.OUT)

def ledON():
    GPIO.output(ledPin, True)
    sleep(sleepTime)
    GPIO.cleanup()

def callLED():
    ledSetup()
    ledON()

cookieServer2.py

import socket
from cookieLED import callLED

host = ''
port = 5560

storedValue = "Yo, what's up?"

def setupServer():
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    print("Socket created.")
    try:
        s.bind((host, port))
    except socket.error as msg:
        print(msg)
    print("Socket bind comlete.")
    return s

def setupConnection():
    s.listen(1) # Allows one connection at a time.
    conn, address = s.accept()
    print("Connected to: " + address[0] + ":" + str(address[1]))
    return conn

def GET():
    reply = storedValue
    return reply

def REPEAT(dataMessage):
    reply = dataMessage[1]
    return reply

def dataTransfer(conn):
    # A big loop that sends/receives data until told not to.
    while True:
        # Receive the data
        data = conn.recv(1024) # receive the data
        data = data.decode('utf-8')
        # Split the data such that you separate the command
        # from the rest of the data.
        dataMessage = data.split(' ', 1)
        command = dataMessage[0]
        if command == 'GET':
            reply = GET()
        elif command == 'REPEAT':
            reply = REPEAT(dataMessage)
        elif command == 'LED_ON':
            callLED()
            reply = 'LED was on'
        elif command == 'EXIT':
            print("Our client has left us :(")
            break
        elif command == 'KILL':
            print("Our server is shutting down.")
            s.close()
            break
        else:
            reply = 'Unknown Command'
        # Send the reply back to the client
        conn.sendall(str.encode(reply))
        print("Data has been sent!")
    conn.close()
        

s = setupServer()

while True:
    try:
        conn = setupConnection()
        dataTransfer(conn)
    except:
        break