The Touchstone is an open hardware and software indoor environmental quality sensor designed by the National Association of REALTORS/CRT Labs. The idea behind the Touchstone was conceived in the summer of 2016, when we at CRT Labs were exploring various types of personal air quality monitors available in the market. We found that most of them were around $150-$200 for one device, costing a lot more in some cases. They used cheap sensors that weren’t accurate, and almost all had a dependency on a combination of a smartphone app and some cloud platform on the internet that it pushes data to. If we want to monitor the environmental quality of the entire home, we would have to spend around $200 for each room and give up privacy for the sake of cloud access to our data.

The Rosetta Home 2.0 platform developed by CRT Labs aims to solve exactly this issue. We developed it with an offline first mentality – no internet required. Cloud connectivity is optional for data backup, large-scale research and more in-depth data analysis. You are not locked into any one cloud provider or a mobile platform. With the addition of the Touchstone, a home’s environmental quality can now be monitored locally, accurately, and at a relatively affordable price.

A Touchstone can measure the local temperature, relative humidity, carbon dioxide concentration, TVOC (total volatile organic compound) concentration, PM2.5 (particulate matter) mass concentration, sound intensity, light intensity and barometric pressure. With advancement in MEMS and CMOS technology, we now have access to sensors that are extremely cheap and have decent accuracy, and more are being available every day. In order to find the right balance between price and performance, several sensors are tested along with higher-end reference sensors that we know are accurate from literature review of other studies. Sample CO2 data from one of our sensor tests is shown in the graph below:

From the graph, we can see that the sensors can vary widely in the readings. Similar tests are being done for other parameters that we measure. We found that some of the sensors that report incorrect values are currently being used in popular air quality monitors in the market today. Our goal is to maintain relatively high accuracy in sensor readings. This allows our Touchstone devices to be used in large-scale research projects that can provide large data-sets of anonymous environmental quality for different types of climate zones and different types of homes across the country. Ultimately, the goal is to yield useful correlations between this hyper-local data and energy use and human activity.

The Touchstone devices wirelessly send data to a receiver that’s also on the same network. For wireless transmission, an FSK radio transceiver running at 915MHz frequency is used. This frequency band is license-free and set as an ISM band for commercial and industrial products. Using a dedicated transceiver as opposed to relying on commonly used protocols that operate in the 2.4GHz bands such as WiFi, ZigBee, Bluetooth and others allows for robust, low-power and long-range wireless operation. The radio modules have a transmission range of over 500 m in open air and over 150-200 m in occupied buildings. Due to their operation in the sub-GHz frequency bands, they have much better obstacle penetration, greater reception and stronger immunity to the ever increasing RF noise in the spectrum. This contributes to superior performance for the specified application of data logging within buildings. Using dedicated radios also eliminates dependencies on internet access (wired or wireless) on every sensor location as well as electric power in some cases where the sensor can run on batteries for several years at a stretch. Currently, the Touchstone runs on a 5V USB power supply, the same one we use for charging our cell phones. There are application-specific versions currently in development that allow for lower power versions of these boards. The Touchstone and other boards in its family can all be made relatively cheaper than their commercial counterparts.

The gateway receiver has the same radio module which constantly monitors all incoming wireless sensor data from around the building and pushes it over USB to the Rosetta Home platform running on a Raspberry Pi. The data can then be aggregated and monitored in real-time locally, and also pushed to the cloud for remote-monitoring and research purposes if necessary.

Currently, we are designing and testing various types of enclosures at a manufacturing facility called mHUB here in Chicago. Here’s a Touchstone prototype in its enclosure and its relative size in the average hand:

This is how the assembled boards looks like without the enclosure:

The assembly of the board is currently done manually at CRT Labs, as we are iterating over the hardware design and as sensor tests yield more data. Over the next few months, the assembly of the boards will be done at mHUB, which has factory-grade equipment using which the production can scale to several hundred units per day. These devices when complete will be used for research studies to be conducted by CRT Labs in Chicago, and later, in various cities around the country in the coming months. The data that comes from this research can give us an insight on how residential and commercial buildings perform across seasons, and how they impact energy usage. Ultimately, this will lead to more energy-efficient, smart and healthier buildings in the near future.