---
title: "Temperature Sensors"
slug: "temperature-sensors"
date: "2024-08-26"
toc: true

pics:
  pico-ws:
    css: "image"
    tip: "Pico Ws with BME280 sensors attached."
    sources:
      - "/files/articles/temperature-sensors/pico-ws-1024.webp"
      - src: "/files/articles/temperature-sensors/pico-ws-1024.jpg"
        width: 1024
        height: 771
  old-sensors:
    css: "image"
    tip: "Original BME280 sensors."
    sources:
      - "/files/articles/temperature-sensors/old-sensors-20180724-1024.webp"
      - src: "/files/articles/temperature-sensors/old-sensors-20180724-1024.jpg"
        width: 1024
        height: 768
  old-pi3:
    css: "image"
    tip: "Bedroom Pi 3 HTPC with BME280 sensor attached."
    sources:
      - "/files/articles/temperature-sensors/old-pi3-20180724-1024.webp"
      - src: "/files/articles/temperature-sensors/old-pi3-20180724-1024.jpg"
        width: 1024
        height: 768
  old-web-ui-1:
    css: "image"
    tip: "Original web interface (2018)."
    sources:
      - "/files/articles/temperature-sensors/old-web-ui-1-1024.webp"
      - src: "/files/articles/temperature-sensors/old-web-ui-1-1024.png"
        width: 1024
        height: 576
  old-web-ui-2:
    css: "image"
    tip: "Improved web interface (2019)."
    sources:
      - "/files/articles/temperature-sensors/old-web-ui-2-20190905-1024.webp"
      - src: "/files/articles/temperature-sensors/old-web-ui-2-20190905-1024.png"
        width: 1024
        height: 765
  web-desktop-0:
    css: "image"
    tip: "Current Data, Charts, and Forecast panels in the desktop web interface (2024)."
    sources:
      - "/files/articles/temperature-sensors/web-desktop-0-1024.webp"
      - src: "/files/articles/temperature-sensors/web-desktop-0-1024.png"
        width: 1024
        height: 640
  web-desktop-1:
    css: "image"
    tip: "Edit Sensor dialog in the desktop web interface (2024)."
    sources:
      - "/files/articles/temperature-sensors/web-desktop-1-1024.webp"
      - src: "/files/articles/temperature-sensors/web-desktop-1-1024.png"
        width: 1024
        height: 640
  web-desktop-2:
    css: "image"
    tip: "Charts panel in the desktop web interface (2024)."
    sources:
      - "/files/articles/temperature-sensors/web-desktop-2-1024.webp"
      - src: "/files/articles/temperature-sensors/web-desktop-2-1024.png"
        width: 1024
        height: 640
  web-desktop-3:
    css: "image"
    tip: "Forecast details dialog in the desktop web interface (2024)."
    sources:
      - "/files/articles/temperature-sensors/web-desktop-3-1024.webp"
      - src: "/files/articles/temperature-sensors/web-desktop-3-1024.png"
        width: 1024
        height: 640

carousel:
  bottom:
    - link: "/files/articles/temperature-sensors/web-mobile-0.png"
      tip: "Current Data panel."
      css: "image"
      sources:
        - "/files/articles/temperature-sensors/web-mobile-0-1024.webp"
        - src: "/files/articles/temperature-sensors/web-mobile-0-1024.png"
          width: 460
          height: 1024
    - link: "/files/articles/temperature-sensors/web-mobile-1.png"
      tip: "Edit Sensor dialog."
      css: "image"
      sources:
        - "/files/articles/temperature-sensors/web-mobile-1-1024.webp"
        - src: "/files/articles/temperature-sensors/web-mobile-1-1024.png"
          width: 460
          height: 1024
    - link: "/files/articles/temperature-sensors/web-mobile-2.png"
      tip: "Charts panel."
      css: "image"
      sources:
        - "/files/articles/temperature-sensors/web-mobile-2-1024.webp"
        - src: "/files/articles/temperature-sensors/web-mobile-2-1024.png"
          width: 460
          height: 1024
    - link: "/files/articles/temperature-sensors/web-mobile-3.png"
      tip: "Forecast Details dialog."
      css: "image"
      sources:
        - "/files/articles/temperature-sensors/web-mobile-3-1024.webp"
        - src: "/files/articles/temperature-sensors/web-mobile-3-1024.png"
          width: 460
          height: 1024

# table data
tables:
  # available table properties
  pins:
    name: "Pins"

    cols:
      - id: "color"
        name: "Wire Color"
        tip: "Wire color."
      - id: "pico"
        name: "Pico W"
        tip: "Pico W pin."
      - id: "bme280"
        name: "BME280"
        tip: "BME280 pin."

    rows:
      - color: "Red"
        pico: "#36, 3V3(OUT)"
        bme280: "VIN"
      - color: "Black"
        pico: "#3, GND"
        bme280: "GND"
      - color: "Yellow"
        pico: "#6, GP4, I2C0 SDA"
        bme280: "SDA"
      - color: "Green"
        pico: "#7, GP5, I2C0 SCL"
        bme280: "SCL"
---
## Introduction

We have several [Raspberry Pi Pico Ws][pico w] throughout the house.
The [Pico Ws][pico w] collect temperature and humidity measurements.
There is a web interface which shows the current measurements, charts of
recent measurements, and the weather forecast for several days.

Here is a picture of the web interface:

[{{< pe-figure "web-desktop-0" >}}][web-desktop-0]

The following sections describe the history of this project, the
hardware, the software on the [Pico Ws][pico w], and the software behind
the web interface.

**Note:** [Home Assistant][] or an [Ecobee][] are both more practical
solutions; this started as a tinkering project that accidentally became
useful for us.

That said, there is some value in controlling all of the hardware and
software; none of our our data leaves our home network, we don't have to
create an account on a ridiculous online hub with a dubious privacy
policy, and we don't have to worry about our [devices being bricked in a
couple of years][bricked].

## History

In 2018 I attached [BME280][] sensors to our [Raspberry Pi 3][pi3]
[HTPCs][htpc] and created a minimal web interface to view the sensor
measurements.

Here is a picture of the original [BME280][] sensors:

[{{< pe-figure "old-sensors" >}}][old-sensors]

Here is the original bedroom [Pi 3][pi3] [HTPC][] with a [BME280][]
sensor attached:

[{{< pe-figure "old-pi3" >}}][old-pi3]

And here is the original web interface (yikes!):

[{{< pe-figure "old-web-ui-1" >}}][old-web-ui-1]

In 2019 I added a third sensor attached to a [Raspberry Pi Zero W][pi0w]
in the basement and outdoor measurements pulled from the [National
Weather Service (NWS) API][nws-api].

I also made several improvements to the web interface:

- Redesigned in [Bootstrap 4][].
- Added [chart.js][]-based charts.
- Added weather forecast from [NWS API][nws-api].

Here is the improved web interface from 2019:

[{{< pe-figure "old-web-ui-2" >}}][old-web-ui-2]

The setup above worked for several years, but the software was a
mishmash of undocumented [Ruby][], [shell scripts][], and [cron][] jobs.

This caused several problems:

- It was difficult to install and difficult to maintain.
- It required a full Raspberry Pi running Linux.  This was fine
  for the dual-use [Pi 3][pi3] [HTPCs][htpc], but it felt like a waste
  of a [Pi Zero W][pi0w].
- The web interface queried the status of all sensors on page load
  (pull model).  This made the page unnecessarily slow.
- The web interface would fail to load when sensors were inactive or
  unreachable.
- The charts in the web interface were not mobile-friendly.
- It collected several measurements that we never used, like [load
  average][loadavg] and network quality.
- The collected data was concatenated to a [CSV][] file rather than
  inserted atomically into a database.  This made it slow and difficult
  to query.
- When we moved we needed more sensors, but  I didn't want to "waste"
  any more [Pi Zero Ws][pi0w] or deal with the hassle of setting up the
  software.

In 2022 I [bought a spool of Pico Ws][bought-pico-ws] to replace the
existing hardware and decided to rewrite the web interface to address
the problems listed above.

The [Pico Ws][pico w] sat unused for a couple of years because I didn't
have a good work area.  In 2023 we lost two of the sensors:

- one failed during a [botched Pi Zero W Bookworm
  upgrade][failed-upgrade].
- one failed for no apparent reason.

In 2024 we set up my [home office][] and I started working on the new
hardware and software.

## Hardware

[Raspberry Pi Pico Ws][pico w] microcontrollers with [BME280s][bme280]
connected via [I2C][].  Here are three of them:

[{{< pe-figure "pico-ws" >}}][pico-ws]

[Fritzing][] is on the fritz for me at the moment so I don't have a
pinout diagram.  Here is a pinout table instead:

{{< table "pins" >}}

## Software

The software is available in the [Sensortron Git repository][repo].
The repository contains two directories:

- `pico-w/`: [Pico W][] [Micropython][] code which periodically collects
  and sends [BME280][] sensor measurements to an [API][] endpoint.
- `web/`: Web interface which shows sensor measurements and the weather
  forecast.


### Pico W

[Micropython][] script in the `pico-w/` directory of the [Sensortron Git
repository][repo] which runs on the [Pico Ws][pico w] and does the
following:

1. Read the configuration from `config.py`.
2. Initialize the [BME280][] sensor attached to [I2C][] bus 0.
3. Connect to the [Wi-Fi][] network.
4. Read sensor values every 10 seconds and send them to an [API][]
   endpoint.

The code for the logic above is in [pico-w/main.py][].

Installation is documented and straightforward:

1. Flash latest [Pico W Micropython image][].
2. Copy `main.py` and `bme280.py` to the [Pico W][].
3. Edit `config.py` and copy it to the [Pico W][].

Here is an example `config.py`:

```python
# diningroom.py: example sensortron configuration file

# wifi ssid and password (required)
WIFI_SSID = 'YOUR-WIFI-SSID'
WIFI_PASSWORD = 'YOUR-WIFI-PASSWORD'

# api url (required)
URL = 'http://sensors.home.pmdn.org:1979/api/read'

# pseudo-mac secret (optional, defaults to '' if unspecified)
SECRET = 'SOME-SECRET-STRING'

# host name (optional, defaults to pico-$UNIQUE_ID if unspecified)
HOSTNAME = 'pico-diningroom'
```

### Web interface

Web interface in the `web/` directory of the [Git repository][repo]
which shows current sensor measurements, a filterable chart of recent
sensor measurements, and the weather forecast for the next several days.

The web interface also exposes an [HTTP][] [API][] endpoint which the
[Pico Ws][pico w] use to submit their current sensor readings.

The appearance of the current web interface is similar to the older 2019
web interface, but with many improvements.

Backend improvements:

- Written in [Go][].
- Two dependencies: [go-chi][] and [modernc.org/sqlite][].
- Web assets are [embedded][embed] in the binary.
- Periodic tasks are handled in [goroutines][] spawned from the binary
  rather than a set of [cron][] jobs.
- Data is stored in a [SQLite][] database.
- Sensors post measurements to an [API][] endpoint (push model).
- Built and deployed as single static binary in a a small (<20M)
  [container][].  The build is [multi-stage][] and the output image is
  based on [distroless][].  Persistent data is stored in one place
  (`/data`) so the container is [volume][]-friendly.

Frontend improvements:

- [Bootstrap 5.3][] and [chart.js 4.4][chart.js].
- Sensor display parameters (name, color, and sort order) are now
  editable via the web interface.
- Charts are now [responsive][] and render correctly on desktop and
  mobile.
- Charts can be downloaded as [PNG][] images.
- Removed unused features. Example: air pressure.
- Added new useful features. Example: probability of precipitation.
- Interface refreshes automatically without a page reload.

The home page loads instantly with these improvements.  It's also much
easier to update, build, and deploy.  Here's the one-liner I use to
deploy, split into multiple lines for legibility:

```sh
# - pull latest code from git repo
# - build image
# - stop old container (if any)
# - start new ephemeral container named "sensortron" which exposes port
#   1979, and uses the "sensortron" volume
git pull && podman build -t sensortron . && (
  podman stop sensortron;
  podman run -d --rm -p 1979:1979 -v sensortron:/data --name sensortron sensortron
)
```
&nbsp;

Here are the current data, charts, and forecast panels on the home page
of the 2024 web interface:

[{{< pe-figure "web-desktop-0" >}}][web-desktop-0]

Edit Sensor dialog:

[{{< pe-figure "web-desktop-1" >}}][web-desktop-1]

Charts panel:

[{{< pe-figure "web-desktop-2" >}}][web-desktop-2]

Forecast Details dialog:

[{{< pe-figure "web-desktop-3" >}}][web-desktop-3]

The web interface is [responsive][] so it works just as well on mobile.
Here are screenshots of the same interface components on my phone:

[pico w]: https://www.raspberrypi.com/documentation/microcontrollers/pico-series.html#raspberry-pi-pico-w
  "Raspberry Pi Pico W"
[I2C]: https://en.wikipedia.org/wiki/I%C2%B2C
  "Inter-Integrated Circuit (I2C)"
[bme280]: https://www.bosch-sensortec.com/products/environmental-sensors/humidity-sensors-bme280/
  "BME280 temperature sensor"
[pico-ws]: /files/articles/temperature-sensors/pico-ws.jpg
  "Pico Ws with BME280 sensors attached."
[pi3]: https://www.raspberrypi.com/products/raspberry-pi-3-model-b/
  "Raspberry Pi 3 Model B"
[htpc]: https://en.wikipedia.org/wiki/Home_theater_PC
  "Home Theater PC (HTPC)"
[old-sensors]: /files/articles/temperature-sensors/old-sensors-20180724.jpg
  "Original BME280 sensors."
[old-pi3]: /files/articles/temperature-sensors/old-pi3-20180724.jpg
  "Bedroom Pi 3 HTPC with BME280 sensor attached."
[old-web-ui-1]: /files/articles/temperature-sensors/old-web-ui-1.png
  "Original web interface (2018)."
[nws-api]: https://www.weather.gov/documentation/services-web-api
  "National Weather Service (NWS) Application Programming Interface (API)"
[pi0w]: https://www.raspberrypi.com/products/raspberry-pi-zero-w/
  "Raspberry Pi Zero W"
[old-web-ui-2]: /files/articles/temperature-sensors/old-web-ui-2-20190905.png
  "Improved web interface (2019)."
[bootstrap 4]: https://getbootstrap.com/docs/4.6/getting-started/introduction/
  "Bootstrap 4 CSS framework."
[chart.js]: https://www.chartjs.org/
  "JavaScript charting library."
[ruby]: https://ruby-lang.org/
  "Ruby programming language"
[shell scripts]: https://en.wikipedia.org/wiki/Shell_script
  "Unix shell script."
[cron]: https://en.wikipedia.org/wiki/Cron
  "Command-line Unix job scheduler."
[loadavg]: https://en.wikipedia.org/wiki/Load_(computing)
  "CPU load average."
[csv]: https://en.wikipedia.org/wiki/Comma-separated_values
  "Comma-separated Value (CSV)."
[failed-upgrade]: {{< relref "posts//2023-06-02-end-of-may-miscellany.md" >}}
  "Failed Pi Zero W Bookworm upgrade."
[bought-pico-ws]: {{< relref "posts/2022-11-11-pico-ws.md" >}}
  "Pico Ws"
[home office]: {{< relref "articles/home-office.md" >}}
  "Home Office"
[repo]: https://github.com/pablotron/sensortron
  "Sensortron Git repository."
[micropython]: https://micropython.org/
  "Micropython programming language"
[go]: https://go.dev/
  "Go programming language"
[container]: https://en.wikipedia.org/wiki/Containerization_(computing)
  "Operating-system-level virtualization."
[sqlite]: https://sqlite.org/
  "Small, fast, self-contained SQL database."
[restful]: https://en.wikipedia.org/wiki/REST
  "HTTP-based API which uses HTTP verbs and adheres loosely to REST"
[api]: https://en.wikipedia.org/wiki/API
  "Application Programming Interface (API)"
[wi-fi]: https://en.wikipedia.org/wiki/Wi-Fi
  "Wireless network."
[Pico W Micropython image]: https://micropython.org/download/RPI_PICO_W/
  "Pico W Micropython image."
[go-chi]: https://go-chi.io/
  "Small web router for building HTTP services."
[modernc.org/sqlite]: https://modernc.org/sqlite
  "cgo-free port of SQLite."
[html]: https://en.wikipedia.org/wiki/HTML
  "HyperText Markup Language (HTML)."
[js]: https://en.wikipedia.org/wiki/JavaScript
  "Javascript."
[css]: https://en.wikipedia.org/wiki/CSS
  "Cascading Style Sheets (CSS)."
[embed]: https://pkg.go.dev/embed
  "embed package in Go standard library."
[goroutines]: https://en.wikipedia.org/wiki/Go_(programming_language)#Concurrency
  "Concurrency in Go."
[bootstrap 5.3]: https://getbootstrap.com/docs/5.3/
  "Bootstrap 5.3 CSS framework."
[multi-stage]: https://docs.docker.com/build/building/multi-stage/
  "Multi-stage build."
[responsive]: https://en.wikipedia.org/wiki/Responsive_web_design
  "Responsive web design."
[distroless]: https://en.wikipedia.org/wiki/Responsive_web_design
  "Minimal container base."
[png]: https://en.wikipedia.org/wiki/PNG
  "Portable Network Graphics (PNG)"
[volume]: https://docs.docker.com/engine/storage/volumes/
  "Persistent data storage for containers."
[web-desktop-0]: /files/articles/temperature-sensors/web-desktop-0.png
  "Current Data, Charts, and Forecast panels in the desktop web interface (2024)."
[web-desktop-1]: /files/articles/temperature-sensors/web-desktop-1.png
  "Edit Sensor dialog in the desktop web interface (2024)."
[web-desktop-2]: /files/articles/temperature-sensors/web-desktop-2.png
  "Charts panel in the desktop web interface (2024)."
[web-desktop-3]: /files/articles/temperature-sensors/web-desktop-3.png
  "Forecast Details dialog in the desktop web interface (2024)."
[http]: https://en.wikipedia.org/wiki/HTTP
  "HyperText Transfer Protocol (HTTP)"
[home assistant]: https://en.wikipedia.org/wiki/Home_Assistant
  "Open source home automation software."
[ecobee]: https://en.wikipedia.org/wiki/Ecobee
  "Company which makes smart thermostats and temperature sensors"
[fritzing]: https://en.wikipedia.org/wiki/Fritzing
  "Open source electronics CAD hardware."
[pico-w/main.py]: https://github.com/pablotron/sensortron/blob/main/pico-w/main.py
  "pico-w/main.py in Sensortron Git repository."
[bricked]: https://arstechnica.com/gadgets/2024/09/ftc-urged-to-make-smart-devices-say-how-long-theyll-be-supported/
  "FTC urged to make smart devices say how long they will be supported (arstechnica.com)"