Esp8266-01 based module, 220V ac powered, for measuring room temperature for your autonomous house. Any possibility of improvement is accepted.
I built this module to have an inexpensive and reliable sensor in every room of my house. Total cost per sensor is around 5.5€ and includes all components and pcb. It does not rely on batteries but on an ac-dc transformer type HLK-PM03.
The design is intended to minimize the dimensions and thus be able to put the sensor inside the power boxes, where there are light switches to be clear. I 3D printed a container to be able to easily insert it in the boxes type btcino and allow the sensor to effectively detect the temperature and humidity outside through some openings.
The module is composed of:
- esp8266-01
- dht11 temperature and humidity sensor
- hlk-pm03 as ac-dc transformer
- 4.7k ohm resistor
- 50uF capacitor
I have also used a JST connector to bring 220v to the board.
The esp is programmed before the insertion in the module thanks to a usb adapter, the following updates can be done over the air thanks to the EspHome software.
I didn't want batteries to power the module so you don't have the bother of changing them and making sure they are charged, plus I think in the long run changing a battery every year or so is not convenient.
However, if that is more suitable for you there will be no problems adding a battery holder and use a 3.3V battery.
I know that DHT11 is not an exceptionally reliable temperature and humidity sensor but for the purpose of this project it is more than sufficient.
For a complete list of parts with some links: https://docs.google.com/spreadsheets/d/1-pkWVYFf2BbrVPfpay5KMb0pS1-IxxCx1xM6d1OcC2A/edit#gid=0
The software used is EspHome to integrate the sensors with my HomeAssistant server but you may as well use another software to your liking.
After adding your new esp device in EspHome, as a generic esp8266 board, the only thing to add in the code is the following:
sensor:
- platform: dht
pin: GPIO2
temperature:
name: "Room temperature"
humidity:
name: "Room umidity"
update_interval: 60s
This allows us to read the values of temperature and humidity and have them as a sensor in our Home Assistant server.
You can add some filters for calibrating dht, this should be done by comparison with a reliable thermometer.
Check the complete .yaml file if you need an example ready to use for your EspHome device.
The design of the pcb has been made with Eagle. The various components were added thanks to libraries found on the internet. For simplicity reasons all the components are through hole and the esp is inserted thanks to female socket header connectors.
In one side of the pcb there are esp and dht11 and in the other hlk and a jst connector for power supply. The intention was to have all soldered on the board but the heat released by the hlk and the esp compromised the reading of temperature and umidity values. For this reason, dht sensor is installed thanks to 10cm cables soldered to the pcb. Some 3 way jst connector could be used to have a nicer design.
The second version of the pcb allows to have larger distance between dht11 and other components and allows to have all soldered in the pcb. If you have more space available inside your switches box, it's preferable to use v2 (but it has not been tested yet).
If you prefer to use battery power you can place a battery holder where there is the hlk and easily make a sensor like the ones ready to use with a lower overall cost.
The purposes of the 3d enclosure are:
- to maintain in a fix position the dht sensor
- to allow proper measurements of the room temperature thanks to openings
- to be able to place the module in a hidden way next to the power switches.
In my home we have btcino switches, so a similar design was needed.
