Setting up your Raspberry Pi and moisture sensor

Insert your microSD card into the Raspberry Pi, connect your monitor, keyboard, mouse, and, if you're not using Wi-Fi, Ethernet cable. Do not connect the power cable yet.

Connect the JST jumper cable to the moisture sensor. The other side of the jumper has four wires:

Green: I2C SCL
White: I2C SDA
Red: power (3.5 V)
Black: ground

Hold the Raspberry Pi with the Ethernet jack on the right. In this orientation, there are two rows of GPIO pins at the top. Connect the wires from the moisture sensor to the bottom row of pins in the following order. Starting at the left-most pin, connect red (power), white (SDA), and green (SCL). Skip one pin, and then connect the black (ground) wire. For more information, see Python Computer Wiring.

Attach the power cable to the Raspberry Pi and plug the other end into a wall socket to turn it on.

Configure your Raspberry Pi

On Welcome to Raspberry Pi, choose Next.
Choose your country, language, timezone, and keyboard layout. Choose Next.
Enter a password for your Raspberry Pi, and then choose Next.
Choose your Wi-Fi network, and then choose Next. If you aren't using a Wi-Fi network, choose Skip.
Choose Next to check for software updates. When the updates are complete, choose Restart to restart your Raspberry Pi.

After your Raspberry Pi starts up, enable the I2C interface.

In the upper left corner of the Raspbian desktop, click the Raspberry icon, choose Preferences, and then choose Raspberry Pi Configuration.
On the Interfaces tab, for I2C, choose Enable.
Choose OK.

The libraries for the Adafruit STEMMA moisture sensor are written for CircuitPython. To run them on a Raspberry Pi, you need to install the latest version of Python 3.

Run the following commands from a command prompt to update your Raspberry Pi software:

sudo apt-get update

sudo apt-get upgrade
Run the following command to update your Python 3 installation:

sudo pip3 install --upgrade setuptools
Run the following command to install the Raspberry Pi GPIO libraries:

pip3 install RPI.GPIO
Run the following command to install the Adafruit Blinka libraries:

pip3 install adafruit-blinka

For more information, see Installing CircuitPython Libraries on Raspberry Pi.
Run the following command to install the Adafruit Seesaw libraries:

sudo pip3 install adafruit-circuitpython-seesaw
Run the following command to install the AWS IoT Device SDK for Python:

pip3 install AWSIoTPythonSDK

Your Raspberry Pi now has all of the required libraries. Create a file called moistureSensor.py and copy the following Python code into the file:



from adafruit_seesaw.seesaw import Seesaw
from AWSIoTPythonSDK.MQTTLib import AWSIoTMQTTShadowClient
from board import SCL, SDA

import logging
import time
import json
import argparse
import busio

# Shadow JSON schema:
#
# {
#   "state": {
#       "desired":{
#           "moisture":<INT VALUE>,
#           "temp":<INT VALUE>            
#       }
#   }
# }

# Function called when a shadow is updated
def customShadowCallback_Update(payload, responseStatus, token):

    # Display status and data from update request
    if responseStatus == "timeout":
        print("Update request " + token + " time out!")

    if responseStatus == "accepted":
        payloadDict = json.loads(payload)
        print("~~~~~~~~~~~~~~~~~~~~~~~")
        print("Update request with token: " + token + " accepted!")
        print("moisture: " + str(payloadDict["state"]["reported"]["moisture"]))
        print("temperature: " + str(payloadDict["state"]["reported"]["temp"]))
        print("~~~~~~~~~~~~~~~~~~~~~~~\n\n")

    if responseStatus == "rejected":
        print("Update request " + token + " rejected!")

# Function called when a shadow is deleted
def customShadowCallback_Delete(payload, responseStatus, token):

     # Display status and data from delete request
    if responseStatus == "timeout":
        print("Delete request " + token + " time out!")

    if responseStatus == "accepted":
        print("~~~~~~~~~~~~~~~~~~~~~~~")
        print("Delete request with token: " + token + " accepted!")
        print("~~~~~~~~~~~~~~~~~~~~~~~\n\n")

    if responseStatus == "rejected":
        print("Delete request " + token + " rejected!")


# Read in command-line parameters
def parseArgs():

    parser = argparse.ArgumentParser()
    parser.add_argument("-e", "--endpoint", action="store", required=True, dest="host", help="Your device data endpoint")
    parser.add_argument("-r", "--rootCA", action="store", required=True, dest="rootCAPath", help="Root CA file path")
    parser.add_argument("-c", "--cert", action="store", dest="certificatePath", help="Certificate file path")
    parser.add_argument("-k", "--key", action="store", dest="privateKeyPath", help="Private key file path")
    parser.add_argument("-p", "--port", action="store", dest="port", type=int, help="Port number override")
    parser.add_argument("-n", "--thingName", action="store", dest="thingName", default="Bot", help="Targeted thing name")
    parser.add_argument("-id", "--clientId", action="store", dest="clientId", default="basicShadowUpdater", help="Targeted client id")

    args = parser.parse_args()
    return args


# Configure logging
# AWSIoTMQTTShadowClient writes data to the log
def configureLogging():

    logger = logging.getLogger("AWSIoTPythonSDK.core")
    logger.setLevel(logging.DEBUG)
    streamHandler = logging.StreamHandler()
    formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
    streamHandler.setFormatter(formatter)
    logger.addHandler(streamHandler)


# Parse command line arguments
args = parseArgs()

if not args.certificatePath or not args.privateKeyPath:
    parser.error("Missing credentials for authentication.")
    exit(2)

# If no --port argument is passed, default to 8883
if not args.port: 
    args.port = 8883


# Init AWSIoTMQTTShadowClient
myAWSIoTMQTTShadowClient = None
myAWSIoTMQTTShadowClient = AWSIoTMQTTShadowClient(args.clientId)
myAWSIoTMQTTShadowClient.configureEndpoint(args.host, args.port)
myAWSIoTMQTTShadowClient.configureCredentials(args.rootCAPath, args.privateKeyPath, args.certificatePath)

# AWSIoTMQTTShadowClient connection configuration
myAWSIoTMQTTShadowClient.configureAutoReconnectBackoffTime(1, 32, 20)
myAWSIoTMQTTShadowClient.configureConnectDisconnectTimeout(10) # 10 sec
myAWSIoTMQTTShadowClient.configureMQTTOperationTimeout(5) # 5 sec

# Initialize Raspberry Pi's I2C interface
i2c_bus = busio.I2C(SCL, SDA)

# Intialize SeeSaw, Adafruit's Circuit Python library
ss = Seesaw(i2c_bus, addr=0x36)

# Connect to AWS IoT
myAWSIoTMQTTShadowClient.connect()

# Create a device shadow handler, use this to update and delete shadow document
deviceShadowHandler = myAWSIoTMQTTShadowClient.createShadowHandlerWithName(args.thingName, True)

# Delete current shadow JSON doc
deviceShadowHandler.shadowDelete(customShadowCallback_Delete, 5)

# Read data from moisture sensor and update shadow
while True:

    # read moisture level through capacitive touch pad
    moistureLevel = ss.moisture_read()

    # read temperature from the temperature sensor
    temp = ss.get_temp()

    # Display moisture and temp readings
    print("Moisture Level: {}".format(moistureLevel))
    print("Temperature: {}".format(temp))
    
    # Create message payload
    payload = {"state":{"reported":{"moisture":str(moistureLevel),"temp":str(temp)}}}

    # Update shadow
    deviceShadowHandler.shadowUpdate(json.dumps(payload), customShadowCallback_Update, 5)
    time.sleep(1)

Save the file to a place you can find it. Run moistureSensor.py from the command line with the following parameters:

endpoint: Your custom AWS IoT endpoint. For more information, see Device Shadow REST API.
rootCA: The full path to your AWS IoT root CA certificate.
cert: The full path to your AWS IoT device certificate.
key: The full path to your AWS IoT device certificate private key.
thingName: Your thing name (in this case, RaspberryPi).
clientId: The MQTT client ID. Use RaspberryPi.

The command line should look like this:

python3 moistureSensor.py --endpoint your-endpoint --rootCA ~/certs/AmazonRootCA1.pem --cert ~/certs/raspberrypi-certificate.pem.crt --key ~/certs/raspberrypi-private.pem.key --thingName RaspberryPi --clientId RaspberryPi

Try touching the sensor, putting it in a planter, or putting it in a glass of water to see how the sensor responds to various levels of moisture. If needed, you can change the threshold value in the MoistureSensorRule. When the moisture sensor reading goes below the value specified in your rule's SQL query statement, AWS IoT publishes a message to the Amazon SNS topic. You should receive an email message that contains the moisture and temperature data.

After you have verified receipt of email messages from Amazon SNS, press CTRL+C to stop the Python program. It is unlikely that the Python program will send enough messages to incur charges, but it is a best practice to stop the program when you are done.

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Document Conventions

Step 4: Create an AWS IoT rule to send an email

Connect to AWS IoT Core