In the previous lesson, we learned about Twilio and how to create an account on Twilio. Now we will write a Python program which will fetch the temperature data collected by Bolt and send SMS if the temperature value goes outside our specified temperature range.

Step 1: Connect the temperature monitoring circuit as we have done in the previous lesson -Hardware connections for temperature monitor.

Step 2: Login into the putty by entering the IP address of your digital ocean droplet.

Step 3: After successful login, create a file named conf.py which will store all the credentials related to Twilio. To create a new file type sudo nano conf.py in the terminal. After that write below code to save all the credentials in a single file.

SID = 'You can find SID in your Twilio Dashboard' 
AUTH_TOKEN = 'You can find  on your Twilio Dashboard' 
FROM_NUMBER = 'This is the no. generated by Twilio. You can find this on your Twilio Dashboard'
TO_NUMBER = 'This is your number. Make sure you are adding +91 in beginning'
API_KEY = 'This is your Bolt Cloud accout API key'
DEVICE_ID = 'This is the ID of your Bolt device' 

Note: You have to replace all the above value with your credentials. You can find the first four value in Twilio dashboard and the last two in Bolt Cloud dashboard.

We store all the credentials in a separate file since it is sensitive data which should not be shared with anyone. Hence it is a good practice to avoid using credentials in code directly. After replacing all the values, save the file using CTRL+X.

Step 4: Now create one more file named temp_sms.py. To do so you have to type sudo nano temp_sms.py in the terminal. Now we will write main code to collect the data from the Bolt and send SMS if it crosses the threshold.

The algorithm for the code can be broken down into the following steps - 

1. Fetch the latest sensor value from the Bolt device.
2. Check if the sensor value is in the range specified in our min and max values.
3. If it is not in range, send the SMS.
4. Wait for 10 seconds.
5. Repeat from step 1.

Code Explanation

• In the code, we first have to import our conf file which has all the credentials. The python json and time libraries are also imported in the same line. Since we have saved our conf file with the .py extension, we can directly import it.

import conf, json, time

• json is a python library used for handling all operations on JSON objects. JSON is nothing but a data communication format widely used on the Internet for sending/receiving data between a client and server. More information on JSON can be found here. Remember, 'json' is the python library used for handling JSON objects and JSON is a data communication format. 
• Now we will import Bolt python library which will let us fetch the data stored in Bolt Cloud. To send the SMS, the Sms library is also imported. The below line of code imports the required libraries.

from boltiot import Sms, Bolt

• In the above line, we are importing two objects. First one is SMS which will be used to send SMS alerts and the other one is Bolt which is used for accessing data from your Bolt device like the temperature reading.
• Now we will initialize two variables which will store minimum and maximum threshold value. You can initialize any minimum and maximum integer limits to them.
• This would send an alert if the temperature reading goes below the minimum limit or goes above the maximum limit similar to the alerts on a Pharmaceutical company's manufacturing line.

minimum_limit = 300 
maximum_limit = 600

• Now to fetch the data from Bolt Cloud, we will create an object called 'mybolt' using which you can access the data on your Bolt.
• For the Bolt Cloud to identify your device, you will need to provide the API key and the Device ID when creating the mybolt object. Since the conf file holds the API key and Device ID variables, you can use them as follows,

mybolt = Bolt(conf.API_KEY, conf.DEVICE_ID)

The above code will automatically fetch your API key and Device ID that you have initialized in conf.py file.

• Now to send an SMS, we will create an object of the same.

sms = Sms(conf.SID, conf.AUTH_TOKEN, conf.TO_NUMBER, conf.FROM_NUMBER)

The above code will automatically fetch your SID, AUTH_TOKEN, TO_NUMBER and FROM_NUMBER that you have initialized in conf.py file. Make sure you have given correct value in conf.py file.

• Since we want to continuously monitor the temperature reading, we will enclose our logic to fetch, compare and send the SMS inside an infinite loop using the `while True:` statement. An infinite loop is a special loop which executes its code continuously since its exit condition is never going to be valid. To exit the loop, we will need to forcibly exit the code by holding CTRL + C.

while True: 
    print ("Reading sensor value")
    response = mybolt.analogRead('A0') 
    data = json.loads(response) 
    print("Sensor value is: " + str(data['value']))
    try: 
        sensor_value = int(data['value']) 
        if sensor_value > maximum_limit or sensor_value < minimum_limit:
            print("Making request to Twilio to send a SMS")
            response = sms.send_sms("The Current temperature sensor value is " +str(sensor_value))
            print("Response received from Twilio is: " + str(response))
            print("Status of SMS at Twilio is :" + str(response.status))
    except Exception as e: 
        print ("Error occured: Below are the details")
        print (e)
    time.sleep(10)

• The code continuously fetches the temperature value using `analogRead` function. Since the sensor is connected to A0 pin of the Bolt, we will execute the analogRead() function on the pin A0.
• The response from the Bolt Cloud using the analogRead() function is in a JSON format, so we will need to load the JSON data sent by the cloud using Python's json library.
• The temperature value is inside a field labelled as "value" in the response. We can access the JSON values using the statement `sensor_value = int(data['value'])`. This line also converts the sensor reading to integer data type for comparing the temperature range.
• This is enclosed inside a try-except block to handle any error that may occur in the code. More explanation of try-except code block is given here.
• The next line of code checks if the temperature reading is above the maximum limit or below the minimum limit. If it exceeds, then the SMS will be sent.
• The SMS to be sent will contain the text "The Current temperature sensor value is" followed by the temperature value.
• The response from Twilio will be stored inside the `response` variable.
• Once the temperature reading has been sent, we will need to wait for 10 seconds to get the next reading. For this, we will put the program to sleep once every loop iteration.
• The statement `time.sleep(10)` puts the program execution on hold for 10 seconds. This means that the program would not execute for a period of 10 seconds.

In the above code, we are fetching the data every 10sec. You can change the value but ideally, it should be good if the time interval between 2 data points is more than 10sec.

Below is the complete code:

import conf
from boltiot import Sms, Bolt
import json, time

minimum_limit = 300
maximum_limit = 600  


mybolt = Bolt(conf.API_KEY, conf.DEVICE_ID)
sms = Sms(conf.SID, conf.AUTH_TOKEN, conf.TO_NUMBER, conf.FROM_NUMBER)


while True: 
    print ("Reading sensor value")
    response = mybolt.analogRead('A0') 
    data = json.loads(response) 
    print("Sensor value is: " + str(data['value']))
    try: 
        sensor_value = int(data['value']) 
        if sensor_value > maximum_limit or sensor_value < minimum_limit:
            print("Making request to Twilio to send a SMS")
            response = sms.send_sms("The Current temperature sensor value is " +str(sensor_value))
            print("Response received from Twilio is: " + str(response))
            print("Status of SMS at Twilio is :" + str(response.status))
    except Exception as e: 
        print ("Error occured: Below are the details")
        print (e)
    time.sleep(10)

Note: The above "sensor_value" is the raw temperature reading, obtained from the LM35 sensor. In case you want to convert this value to the temperature in degree Celsius, use the formula: 

Temperature=(100*sensor_value)/1024 

Where sensor_value is the variable in which data obtained from the LM35 sensor is stored.

• Save the file. Time to run the code. To do so type `sudo python3 temp_sms.py` in terminal

Please note that SMS delivery via a trial Twilio account is NOT guaranteed to be instant by Twilio. Also, note that SMS will NOT be sent to numbers which have DND(Do Not Disturb) turned ON. It usually takes a few minutes for your SMS to be sent to your mobile number. Please check the logs on Twilio if you are not receiving the SMS even if the temperature exceeds the threshold.

Since we have written a couple of print statement in the code. So the temperature data will get printed on the terminal. If that value falls outside the threshold range then SMS will be sent to your registered number. The screenshot for the SMS sent is given below:

How was the lesson? Isn't it easy? Thanks to Bolt Library which makes this lesson very easy to collect the data and send SMS. In the next lesson, we will learn how we can do the same thing by sending an email instead of SMS.