I wanted to add an LCD screen to my CO2 sensor, so I bought a white LCD 1602 with an I2C controller. The I2C controller needs to be soldered to the LCD, but my basic soldering skills were sufficient for the task.
I also wanted to place it in a box, so I purchased this plastic enclosure but I cannot recommend it. It required a lot of glue from a glue gun to install the LCD and the ESP. I also had to use the soldering iron to create space for the ESP and a hole for the USB connector. I installed the plastic buttons but they are only decorative.
I made room for the sensors inside the box, but finally left them outside because they are more precise that way.
The ESP32-WROOM-32 was too large for the enclosure, so I used a ESP32-C3 Supermini with an expansion board. This is a really amazing board with a 32-bit RISC-V 160MHz microcontroller, WiFi, Bluetooh, I2C and UART. It’s not as powerful as the ESP32-WROOM-32 with a dual core 32-bit Xtensa 240Mhz, but it’s more than capable to control the sensors and the LCD.
This is the ESPHome configuration, which includes a switch to control the LCD backlight and a clock synchronizing the time with Home Assistant:
To keep a healthy environment at home or at the workplace, one of the important things to control is the carbon dioxide (CO2) level.
It’s measured in ppm (parts per million), indicating how many parts of CO2 there are in one million parts of air. As a reference:
Less than 1000 ppm are healthy levels
Between 1000 ppm and 2000 ppm, we need to reduce the CO2 levels
Levels greater than 2000 ppm are associated with headaches, sleepiness, poor concentration, loss of attention…
To reduce the CO2 level, we need to ventilate the room. It can be manually done (opening the windows) or it can be automated with a ventilation system.
To measure it we need a proper CO2 sensor, and one of the most reliables sensors is the MH-Z19B. It is not cheap for the Aliexpress standards (it costs around 20 EUR), but other cheap sensors announced as “air quality” sensors or “eCO2” sensors are not really measuring the CO2 level (i.e. the MQ135).
I bought this MH-Z19B from Aliexpress and hooked it to an ESP32-WROOM-32 board. This board is going to be also purposed as a temperature and humidity sensor, so I also attached a DHT22 sensor. I bought this DHT22 sensor but it is not an original one, and the measures do not seem very correct, so I ordered again an original AM2302 (=DHT22). The MH-Z19B includes a temperature sensor, but it’s mainly used for calibration and it lacks precision, as it does not report decimals. I’m also using an expansion board to simplify the connections.
The ESP32-WROOM-32 on the expansion board connected to the MH-Z19B (gold) and to the DHT22 (red)
The jumper in the expansion board needs to be set to 5V (because both of these sensors need 5V).
Connected VCC and GND of both sensors to the expansion board
Connected the RX and TX of the MH-Z19B to the TX and RX (GPIO1 and GPIO3) of the ESP
Connected GPIO16 to the DAT of the DHT22
Finally, I installed ESPHome to the board with this configuration:
The heating system is in a different builng than the router and I was experiencing some WiFi coverage issues (the WiFi signal needs to cross two metallic window blinds…).
To diagnose the WiFi coverage is very useful the wifi_signal sensor in ESPHome:
sensor:
- platform: wifi_signal
name: Wifi Signal
update_interval: 60s
It was showing a WiFi signal of -95 dBm in the board: This is very low, and it was experiencing some disconnections.
Usually the ESP32 boards have an antenna integrated in the board, but the ESP32-WROOM-32U has an IPEX connector for an external antenna:
So, I spent less than 10 EUR in Aliexpress buying (affiliate links):
I bought from a popular chinese store a generic Tuya smart plug with power monitoring. It was extrememly cheap, costing less than 4 EUR. And of course I bought it to play trying to flash ESPHome.
The first challenge was to open it without breaking it. I was able to open it by wrapping it in cardboard and gently tapping it with a hammer around the body.
You never know what chip you are going to find. In the past ESP8266 was very common but now they switched mainly to Beken chips. This smart switch has a T102_V1.1 board with a Realtek RTL8710BX chip:
Luckily the support for this chip was developed in the LibreTiny project:
After the flashing, if I try to power it from USB the WiFi module did not start and it causes a boot loop, but It worked perfectly plugging it into the mains power. A new device appeared in the router and I can connect to the ESPHome web dashboard.
Adding power metering
The plug includes a power metering chip: the BL0936, that is supported by ESPHome:
However, after configuring and uploading the firmware with the power meter enabled to the board, the device enters a boot loop, displaying the following error:
[D][switch:016]: 'Smart Plug 1' Turning OFF.
[D][binary_sensor:034]: 'Button': Sending initial state OFF
[C][hlw8012:014]: Setting up HLW8012...
W [ 0.109] CHANGE interrupts not supported
Luckily, after 10 reboots, the firmware enters in the “OTA safe mode”, disabling all the modules and connecting to the WiFi without the web dashboard but opening a port to allow remote flashing.
It can be fixed with the workaround of SuperXL2023 modifying the .esphome/platformio/platforms/libretiny/cores/realtek-amb/arduino/src/wiring_irq.c file and adding the lines 64 and 65:
In the ESPHome config I’m specifying the version of the framework to avoid losing this fix in an automatic update. It works perfectly after rebuilding the image with this fix and uploading it to the device.
This is the complete ESPHome configuration with power metering:
It needs to calibrate the sensor to obtain the proper values of voltage_divider, current_resistor and current_multiply. It can be done with a multimeter and entering the values in the hlw8012 page.
I’ve never been a fan of the Raspberry Pi. In my opinion, it occupies an intermediate position where it is too underpowered for desktop use and too overpowered for IoT projects:
To use them as a desktop, there are great X86 alternatives available at about the same price than a RPi 5 but much more powerful, such as the Intel N100.
And for IoT projects, the ESP32 is the king, with amazing boards with Wifi, Bluetooth, etc., all at a price of less than 5 euros.
So it’s place may be TV boxes (where I prefer a Chromecast with Android) or small servers where the power consumtion is important because they are always on.
I bought an Orange Pi 3B: 4 cores, 4GB RAM, 64GB eMMC (~50 euros in Aliexpress) to replace my old X86 home server (Intel N450: 2 cores, 2 GB RAM, 64GB SSD):
The Orange Pi 3B shares the form factor with the Raspberry Pi 3B but it is almost as powerful as the Raspberry Pi 4. Notably, the Orange Pi 3B comes with several advantages over the RPi 4:
Support for eMMC (much faster and reliable than SD cards)
A power button
A full-size HDMI port
External antenna
And it’s cheaper
I installed the Ubuntu Jammy server image in the eMMC following the OPi manual. It needs to use a USB-A male to USB-A male cable and the RKDevTool (it’s in Chinese) that runs only in Windows.
And, as this machine is going to be exposed to internet, I hardened a bit the security:
Changed the APT repositories to ports.ubuntu.com
Regenerated SSH server keys
Removed SSH root access
Changed passwords
Renamed the orangepi user
Removed the local autologin
To remove the local autologin we need to edit:
/lib/systemd/system/getty@.service.d/override.conf: For the display console autologin
/lib/systemd/system/serial-getty@.service.d/override.conf: For the serial console autologin
