Kalle Ott

Kalle Ott

IoT — Building an automated greenhouse Pt. II

In the last session we connected a soil moisture sensor to the cloud and can collect its data now. But these values are not very useful without any reference value to tell it stands for dry or wet soil. Because this reference value depends on the type of soil you are using (mineral content, density,...) and the actual sensor, this value should not be hard coded and easy to change. That's why today we will add an interface to configure the reference value of dry soil. In the next and last session we will add a firebase function to trigger an action to tell you that you have to water the plants again.

As soon as you write data to a database with a form over the internet you should protect your database by authentication. With firebase you can do this by editing the rules to access the firestore. Instead of just setting it to false, like the last time for write access, you can can check if request.auth.uid is not equal null so the request comes from any authenticated user. If you want to limit access to only one specific account you can also check for one specific user id.

service cloud.firestore {
  match /databases/{database}/documents {
    match /{document=**} {
      allow write: if request.auth.uid != null;
      allow read: if request.auth.uid != null;

Now you have to implement an authentication mechanism in the web app, which is fortunately done at the largest part by the firebaseui-web package and with react you can use firebaseui-web-react. To use this there is a prerequisite, you have to enable an authentication mechanism

add a user to firebase

and create an account.

add a user to firebase

To get the actual authentication capabilities in the web app you have to add the firebase/auth package to the other firebase imports:

import firebase from "firebase/app";
import "firebase/firestore";
import "firebase/auth";

With the auth package you can get the authentication state by subscribing to with the onAuthStateChanged function:

  componentDidMount() {
    this.unsubscribe = firebase.auth().onAuthStateChanged(
      user => {
        this.setState({ user })

In the render method of the App component you now can render conditionally the sign in view or the actual app content:

import firebase from 'firebase/app'
import 'firebase/firestore'
import 'firebase/auth'
import FirebaseAuth from 'react-firebaseui/StyledFirebaseAuth'
  render() {
    return (
          <h1>My Greenhouse</h1>
        {this.state.user ? (
          <AppContent />
        ) : (
              signInOptions: [firebase.auth.EmailAuthProvider.PROVIDER_ID]

With the authentication done, the next step is to actually set the reference value that will be used to determine if the soil is dry or wet. To safe a value with the key dryReference in the collection settings on the document soilData you can use the following snippet:

const updateDryReference = (firestore) =>
  // debounce the actual update function to save database writes
  debounce((dryReference) => {
      .set({ dryReference });
  }, 250);

According to updating a value you can of course again subscribe to the changes:

const subscribeToReferenceValue = (
) => {
  return firestore
    .collection("settings") // choose the collection of your data
    .doc("soilData") // choose the document
    .onSnapshot((documentSnapshot) => {
      if (documentSnapshot.exists) {
        // read the actual data and give it to the onUpdate function

With the Slider component from the @material-ui/lab/Slider package you can create a slider UI to change the value stored in the firestore

  render() {
    return (
      <div className="dry-reference-form">
        <p>Dry Reference: {this.state.dryReference.toFixed(2)}</p>
          onChange={(_, dryReference) => {
            this.setState({ dryReference },
              // after setting the local state send
              // the new value to the remote data store
            () => {


  • protect the firestore data access to authenticated users only, or your account
  • extend the data visualization app with authentication
  • implement a component to control the dryReferenceValue

For a sample implementation you can look at: github.com/kaoDev/kalleott.de/tree/master/samples/greenhouse