Co2 Monitor

CO² Monitor Status: stable
Beschreibung	IoT CO² Sensor
Autor:	foosinn, schinken
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ESP Home & ESP C3 Super Mini Version

Description

Since migrating to Homeassistant we have also migrated all of our ESPs to ESPHome. This allowes easy maintenance and OTA updates.

We have also designed a custom case to house the ESP C3 and the Cables.

Hardware

As before you have to solder one additional Pin to the TFA Dostmann CO2-Sensor AirCO2ntrol Sensor.

Wiring

Sensor	Usage	ESP32 C3 Super Mini
Top pin	Ground	GND
Second pin	Clock	Pin 6
Third pin	Data	Pin 5
Lowest pin	Power	5V

We have designed a case which provides additional space for the sensor. You can download the backplate form Printables or Onshape

Software

Extend you ESPHome config using this code block.

sensor:
  - platform: zyaura
    clock_pin: 5
    data_pin: 6
    co2:
      name: "Hackcenter CO2"
    temperature:
      name: "Hackcenter Temperature"

DIY Version

Description

Someday a TFA Dostmann CO2-Sensor AirCO2ntrol appeared in our hackerspace - but the CO² reading couldn't be easily acquired through USB or any other connector. There are some implementations using python or nodejs, but they require a raspberry pi or at least a PC nearby to read the values to publish and store them somewhere.

Nowadays ESP8266, NodeMCU or in our case a Wemos D1 mini (which also has a ESP8266 on it) exist and is totally suitable for the job! Sadly, on the TFA Dostmann there's only a USB interface on the outside, and our Microcontroller does not support USB natively. So we opened the sensor and found a "CALIB" interface

Hardware

Inside the TDA Dostmann CO² sensor, there's a CALIB interface, which consist of four PINs. GND and 5V can easily be determined using a multimeter with continuity test. These PINs are directly connected to the USB port and can be used to power our microcontroller. The other 2 PINs in the middle seem to send some data. After connecting them to a oscilloscope one PIN was obviously just clock, and the other data.

• 

  LTR: GND, Clock, Data and 5V

• 

  Add wires

• 

  Connected!

Test readings using SIGROK and a logic analyser can be found on b4ckspace/esp8266-co2monitor/sigrok-captures.

Software

The signals look like they're just I2C, but actually they're not. Using the scope to decode the data failed - the same is true using the Wemos. After wiring up the sensor to the Wemos we used an external interrupt on the clock pin and a digitalRead on the data pin which is basically "bit banging".

The results were promising: Using a simple python script and the documentation from another manufacturer, we were able to verify the checksum. Also implementing the decode of the data was quite simple using the PDF:

case 0x50:
 co2Measurement = (data[IDX_MSB] << 8) | data[IDX_LSB];
 break;
case 0x42:
 temperature = ((data[IDX_MSB] << 8) | data[IDX_LSB]) / 16.0 - 273.15;
 break;

The last thing to do was connecting to wifi and publishing the data on MQTT. The source code can be found on GitHub and is licensed under the MIT-License.