@daniel.john.edge thanks for sharing the information. It is a cool project you got.
BME680 has closed source library that perform additional signal processing to give indoor air quality measurement as well as estimated of a couple gas value. Without using the library, we can only get raw reading of the "gas sensor". With the Zigbee platform that I am working on, this closed source library is not available.
The raw value of the gas sensor may be a reasonable estimation to start with. It may not have all the bell and whistle of the detail data. However, there could be a threshold where it would indicate a bad/good air quality. Bosch called it a gas sensor. Typically, a gas sensor is a resistive sensor. They way it work is to heat up an element. Then, measure the resistance of this heating element. The theory is that the gas surrounding the heating element will change the resistance while it is heated. BOSCH manage to shrink the sensor to a very small size. I also trust that BOSCH with the German spirit has also figure out the precision.
This is probably a good time to bring up that there are other solutions as well. It may not be small, precise and sexy as the Bosch solution. But, it is cheap. There is a variety of MQX sensors that would plug right into the Environment Sensor Analog input. Amazon has a lot of assortment of these. Here is an example.
I play around with one of them. It is a MQ9. I have a DTH for it as an example to use the Environment Sensor Analog input.
If there is enough interest to go this route, I can revive the topic and document it better. In term of cost, this is probably the most cost effective way to detect gas in your home.
Just a warning, the MQX solution is not sexy. There will be wire to connect. It also detect sensitive to smaller set of gas per MQX type. You would use MQ9 for Carbon Monoxide, Coal Gas, Liquefied Gas. You have to use MQ2 for Combustible Gas, Smoke. In comparison, I do not know how many type of GAS the Bosch sensor is sensitive to. In term of basic fundamental how it work, they should be similar. Bosch may just have perfect it.
In the meantime, the BME680 is still very high on my list to be worked on with Environment Sensor. In short term, I will try to get some Environment Sensor with BME280 unpopulated. I will try to get BME680 on it. I may also have some solution in the medium term if you really need to have the more accurate BME680 gas reading using dual MCU.
In long term, I am working on much newer platform for my Zigbee sensor based on NRF52840. The Bosch closed source library should be use able in this platform. I am really excited with NRF52840. You may have seen my Bluetooth gateway with this platform. I have a few thing line up with this platform in Zigbee and Bluetooth at the same time running on one NRF52840.
I also want to express my thanks to everyone here. Your support and purchases allow me to fund my hobby in making sensor for the community. In this holiday season and the spirit of Thanks Giving, I thank full for this community in supporting my work and hobby.
Thanks
Iman