All ANAVI Gas Detector kits include a MQ-135 analog gas sensor module for detecting air quality. According to the data sheet of MQ-135, the sensitivity characteristics of the sensor depend on temperature and humidity. Because of this, the Advanced and Developer kits of ANAVI Gas Detector also include a HTU21D I2C temperature and humidity sensor module. It has accuracy of ±1°C from -30°C to 90°C and for humidity +/- 2% with an operating range that’s optimized from 5% to 95% RH. Furthermore, the developer kit includes BMP180 I2C sensor module capable for not only measuring temperature but also barometric pressure.

ANAVI Gas Detector is an entirely open source product and there are backers from all around the world. The Celsius temperature scale, also known as the centigrade scale is used worldwide but in the United States and a few other counties Fahrenheit scale is preferred. For everyone’s convenience, the default Arduino sketch for ANAVI Gas Detector supports both Celsius and Fahrenheit.

I have published a short video tutorial to explain how to switch from Celsius to Fahrenheit or vice-versa. The same approach for supporting Celsius and Fahrenheit has been already also implemented for ANAVI Thermometer.

You can type in the preferred temperature scale during the initial setup of ANAVI Gas Detector. By default it is set to Celsius. After that, at any time, you can change the temperature scale though MQTT message.

To change the temperature scale via MQTT, publish a message with topic cmnd/<machine-id>/tempformat. Please note that <machine-id> has to be replaced with the actual machine ID which is shown during the initial configuration and in the serial output on each boot. If you have missed to save the machine ID during the initial configuration, just attach USB to UART cable to ANAVI Thermometer, start Serial Monitor in Arduino IDE (or any other convenient for you software for serial communication) and restart the board (by plugging in and out the USB to microUSB cable).

The payload of the MQTT message contains JSON:

• For Celsius: { "scale": "celsius" }
• For Fahrenheit: { "scale": "fahrenheit" }

For example, to change the temperature scale of ANAVI Thermometer with machine ID with zeros (obviously fake ID just for the example), using mosquitto_pub (provided by mosquitto-clients package in Debian based GNU/Linux distributions) client type in a terminal:

mosquitto_pub -h iot.eclipse.org -d -p 1883 -t 
"cmnd/00000000000000000000000000000000/tempformat" -m '{ "scale": "celsius" }'

For more details please have a look at the YouTube video.

Thank you very much for supporting the crowdfunding campaign of ANAVI Gas Detector! If you haven’t ordered yet, you still have a few days before the end of the campaign. Order now and stay tuned for more updates!

Thanks,
Leon