Temp/Humidity IoT - Part 1

Winters in the midwest can be pretty dry, and I’m particularly susceptible to the dry air. In order to keep the humidity at the ideal level I went on the hunt for a humidity sensor. Then I thought to myself, “that’s a bit too easy”, and decided I could build my own.

Tools

The raw materials we use to build our vision 🏗️

Raspberry Pi Zero W

https://www.adafruit.com/product/3708

16 GB MicroSD Card

https://amzn.to/2sE2PPz

Raspbian Lite

https://www.raspberrypi.org/downloads/raspbian/

DHT22 Temperature and Humidity Sensor

https://www.adafruit.com/product/393

Installation

The Raspberry Pi Zero doesn’t a full HDMI or USB-A port. This makes it slightly harder to just hook it up to a monitor and keyboard as I didn’t have the adapters. Also, I’m a bit lazy. So I looked for an option that would allow me to preconfigure SSH and Wi-Fi so I could just connect to the Pi to continue the setup.

I followed this guide

The highlights are below:

Use Etcher to burn the image to the SD card https://www.balena.io/etcher/

Mount the SD card, and create an empty file called ssh in the /boot directory

This tells the Pi to enable SSH on first boot

Create a file call wpa_supplicant.config in the /boot directory

On first boot the Pi will copy this file and use it to connect to the network

Add the following information to the wpa_supplicant.conf file

country=US
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

network={
    ssid="NETWORK-NAME"
    psk="NETWORK-PASSWORD"
}

Eject the SD card, put it in the Pi, boot up, and SSH into it 😀

Create a simple Python web service

Ultimately we will end up using Python to talk to the sensor, but that will come later. For now, we will just create a simple web service to prove out our setup.

I followed this guide

I made a couple tweaks, so I’ll summarize below

Create the App

SSH into the Pi and install some things to get us going

sudo apt-get install vim nginx supervisor python3 python3-venv

Next, let’s create a place to store our code

sudo mkdir -p /opt/myapp

And move into that directory

cd /opt/myapp

Create a virtualenv and activate it

python3 -m venv envsource env/bin/activate

Let’s install some pip packages

pip install Flask gunicorn

Then create our app

from flask import Flask

app = Flask(__name__)

@app.route('/')
def index():
    return "Hello World"

if __name__ == '__main__':
    app.run(port=8080)

Install the App as a service

Next we’re going to use Supervisor to run our app as a service

Edit the /etc/supervisor/conf.d/supervisor.conf file and add it this to the end

[program:myapp]
directory=/opt/myapp
command=/opt/myapp/env/bin/gunicorn app:app -b localhost:8080
autostart=true
autorestart=true
stderr_logfile=/var/log/myapp/myapp.err.log
stdout_logfile=/var/log/myapp/myapp.out.log

⏭️ In Part 2 we will look at attaching the sensor and reading data