Real Time Graph using AWS Services (Part 1)

Flentas Tech 25th February 2021 - 6 mins read


In this project we are going to use Load Cell and HX711 Amplifier with Arduino and Raspberry Pi to build a real time graph system using AWS Services. We are using Load Cell as a sensor since it gives data in high frequency which we can see changing on graphs easily. We have seen these pressure sensing gates at many malls and showrooms, which automatically opens when someone is standing near the door and get closed after that person is gone. Also in hospitals as weight scale

Required Components:

  • Raspberry Pi (any model should work)
  • Load cell (10Kg)
  • HX711 Load cell Amplifier Module
  • Power source or power bank
  • Connecting wires
  • Breadboard
  • Nut bolts, Frame and base

Load Cell and HX711 Weight Sensor Module

Load cell is transducer which transforms force or pressure into electrical output. Magnitude of this electrical output is directly proportion to the force being applied. Load cells have strain gauge, which deforms when pressure is applied on it. And then strain gauge generates electrical signal on deformation as its effective resistance changes on deformation. A load cell usually consists of four strain gauges in a Wheatstone bridge configuration. Load cell comes in various ranges like 5kg, 10kg, 100kg and more, here we have used Load cell, which can weight upto 40kg.

Now the electrical signals generated by Load cell is in few millivolts, so they need to be further amplify by some amplifier and hence HX711 Weighing Sensor comes into picture. HX711 Weighing Sensor Module has HX711 chip, which is a 24 high precision A/D converter (Analog to digital converter). HX711 has two analog input channels and we can get gain up to128 by programming these channels. So HX711 module amplifies the low electric output of Load cells and then this amplified & digitally converted signal is fed into the Arduino to derive the weight.

Load cell is connected with HX711 Load cell Amplifier using four wires. These four wires are Red, Black, White and Green/Blue. There may be slight variation in colors of wires from module to module. Below the connection details and diagram:

  • RED Wire is connected to E+
  • BLACK Wire is connected to E-
  • WHITE Wire is connected to A-
  • GREEN/BLUE Wire is connected to A+

Connect Load Cell with HX711 and Arduino like below.

Now since our Load Cell is connected to Arduino, we have to code Arduino board to communicate it with load cell.

For this we will have to download HX711 arduino library.

Download the library from the link, and add it to arduino libraries folder.

Below is the code to upload on arduino. (Code will work on any arduino platform if DT and SCK are connected on digital 3,4 pins respectively.)

#include "HX711.h" #define DOUT 2 #define CLK 3 HX711 scale; long int value; float calibration_factor = 166; //-7050 worked for my 440lb max scale. Calbibration factor may be different in your case. void setup() { Serial.begin(9600); scale.begin(DOUT, CLK); scale.set_scale(calibration_factor); scale.tare(); //Reset the scale to 0 long zero_factor = scale.read_average(); //Get a baseline reading } void loop() { value = scale.get_units(), 1; if(value<0){ value = 0; } Serial.print(value); //scale.get_units() returns a float Serial.println(); }

Creating Thing on AWS IoT Core:

  • Create an object in the AWS IoT console via “Manage→Things” and then “Register a thing”.

  • Name your thing and Click “Next”

  • You will be given 4 options for creation of certificates. You can bring your own certificates or you can download certificates created by AWS IoT’s Certificate Authority.

  • For this tutorial, we are downloading certificate created by AWS IoT’s Certificate Authority. Download all certificates also private key and Amazon Root CA. This will be used to authenticate with AWS IoT MQTT Broker. Click on “Activate” to acitivate those certificates.

  • After that, click on attach policy. You will have to attach policy which is used to restrict the thing to perform task associated with that only. For this tutorial we are going to attach unrestricted policy, which states that the thing will be able to send data on any topic.
  • { "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": "iot:*", "Resource": "*" } ] }

Now we are done with IoT Core setup. We can now proceed to setup our Raspberry Pi.

Setting up Raspberry Pi

Following are steps to setup Raspberry Pi:

  • Go through this link for Initial setup of Raspberry Pi.
  • Once your raspberry pi is booted up, connect your Arduino Uno board to Raspberry Pi.
  • Arduino interface will be assigned to ‘/dev/ttyUSB*’. (I.e., /dev/ttyUSB0. It may be assigned to some other USB port if connected any other USB devices to Raspberry Pi).
  • Now your Raspberry Pi is done with setup. It’s time to code your Pi to send data to IoT Core.

Software Setup in Raspberry Pi

  • Install the dependencies
    1. sudo apt-get update
    2. sudo apt-get upgrade
    3. sudo apt-get install python
    4. sudo apt-get install python-pip
    5. pip install paho-mqtt
    6. pip install json
    7. pip install pyserial
  • As we are done with installing all dependencies, its time to code.
  • Create python file which will have all our certificate files and configurations:
  • Create another python file which will connect to Ardunio board and send data to IoT Core through MQTT.
  • import datetime import time import config import logging import serial import json import paho.mqtt.client as mqttClient import ssl #from color_detection import Color_Detection logging.basicConfig(level=logging.DEBUG,format='%(asctime)s %(name)s %(levelname)s: %(message)s') logger = logging.getLogger(__name__) ''' global variables ''' TOPIC = config.AWS_IOT_TOPIC DEVICE_ID = config.AWS_IOT_MQTT_CLIENT_ID SERIAL_PORT = config.AWS_IOT_ARDUINO_SERIAL_PORT READ_INTERVAL = config.AWS_IOT_READ_INTERVAL DID = config.DEVICE_ID arduino_connected_status = 0 connected = False # Stores the connection status BROKER_ENDPOINT = config.AWS_IOT_MQTT_HOST TLS_PORT = 8883 # Secure port DEVICE_LABEL = config.AWS_IOT_MQTT_CLIENT_ID TLS_CERT_PATH = config.AWS_IOT_ROOT_CA_FILENAME # Put here the path of your TLS cert CERTPATH = config.AWS_IOT_CERTIFICATE_FILENAME KEYPATH = config.AWS_IOT_PRIVATE_KEY_FILENAME while True: try: ser = serial.Serial(SERIAL_PORT, 9600) arduino_connected_status = 1 except: logger.error("Arduino Not Connected") arduino_connected_status = 0 time.sleep(1) if arduino_connected_status == 1:"Connected to Arduino") break jsonData = {} counter = 0 ''' Functions to process incoming and outgoing streaming ''' def on_connect(client, userdata, flags, rc): if rc == 0: print("[INFO] Connected to broker") global connected # Use global variable connected = True # Signal connection else: print("[INFO] Error, connection failed") def on_publish(client, userdata, result): # print("Published!") pass def connect(mqtt_client, broker_endpoint, port): global connected if not connected: mqtt_client.on_connect = on_connect mqtt_client.on_publish = on_publish mqtt_client.tls_set(TLS_CERT_PATH, certfile=CERTPATH, keyfile=KEYPATH, cert_reqs=ssl.CERT_REQUIRED, tls_version=ssl.PROTOCOL_TLSv1_2, ciphers=None) mqtt_client.tls_insecure_set(True) mqtt_client.connect(broker_endpoint, port=port, keepalive=60) mqtt_client.loop_start() attempts = 0 while not connected and attempts < 5: # Wait for connection print(connected) print("Attempting to connect...") time.sleep(1) attempts += 1 if not connected: print("[ERROR] Could not connect to broker") return False return True def publish(mqtt_client, topic, payload): try: mqtt_client.publish(topic, payload) except Exception as e: print("[ERROR] Could not publish data, error: {}".format(e)) def init(): mqtt_client = mqttClient.Client() if not connect(mqtt_client, BROKER_ENDPOINT, TLS_PORT): return False return True,mqtt_client connection_status,mqtt_client = init() while 1: if(ser.in_waiting >0): try: jsonData = {} line = '' line = ser.readline() line = line.decode('utf-8') jsonString = json.loads(line) data = int(line) TIMESTAMP = jsonData['DATA'] = data jsonData['TIMESTAMP'] = TIMESTAMP jsonData['TOPIC'] = TOPIC jsonData['DID'] = DID jsonStringForIoT = json.dumps(jsonData,default=str) code = publish(mqtt_client,TOPIC,jsonStringForIoT) except: logger.error("No data over Serial")
  • Now we are done writing code. Run the code. I hope everything works well.

  • Check on IoT Core test page if we are getting data or not.
  • That’s the end of Part one of the project.
  • Summary

    In this post, I’ve shown you how to connect your Load Cell to AWS IoT Core over MQTT on port 8883 and sniffing data from PLC. If you have had a constraint in the past to open port 8883 in your corporate firewalls, you can now use a standard port for HTTPS traffic (443) to send your messages over MQTT to AWS IoT Core endpoint.

    In next part, we are going create AWS IoT Rule to forward data to Kinesis Data Stream. Also, to setup backend and frontend to show real time graph based on sensor data.

    Hope you are doing well. Goodbye for now. Let's meet in next part of this project.

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