From Smartphones to Bluetooth: 12 Years of Sensor Technology to Understand Clean Cooking

Nithya Ramanathan and Martin Lukac founded Nexleaf Analytics in 2009 because they understood that emerging technologies had the potential to revolutionize objective data-gathering throughout the world. With the right tools to operationalize real-time information, governments, researchers, multinationals, and philanthropists would be able to design more agile, responsive, and successful solutions to global problems.

One of the first challenges Nexleaf undertook was monitoring clean cooking. Efficient stoves that can replace traditional cooking practices have tremendous potential to reduce short-lived climate air pollutants (SLCPs) such as black carbon which harms both health and climate. However, the sector had long suffered from a lack of reliable data on how improved cookstoves performed in the field, and whether or not they were actually adopted. Nexleaf asked the question as to whether these improved cookstoves (ICS) could be made “smart” by equipping them with temperature sensors with the capacity to send readings remotely to a cloud server via a network connection. The temperature data could be used to remotely monitor when cooking was happening (a hot stove = a stove in use), how often, and for how long. 

Nexleaf’s first stove monitoring innovation, StoveTrace 1, was launched in 2012 using an actual smartphone in a protective case that sent data via the cellular network. Funding from Qualcomm Wireless Reach supported remote monitoring of a subset of stoves in a clean cookstove distribution in India.

StoveTrace 1 used an Android smartphone and a simple passive circuit with a temperature sensor (thermistor) plugged into the headphone jack. A custom app running on the phone recorded the temperature once every 10 minutes and sent data to the server multiple times a day. Temperature data was processed into cooking events and minutes using an algorithm that identified cooking from the temperature ranges and partners.

StoveTrace 1 performed its function well as proof-of-concept: now the question was how to make the basic principles of the technology more widely usable. With smartphone technology constantly evolving, any phone-based stove monitor design would not last long and could not scale.

In 2015, Nexleaf introduced StoveTrace 5. Building on the proof of concept from the phone-based StoveTrace 1, the ST5 sent data via the cellular network using a SIM card, but in the form of a device that could be mounted on the wall. This device had five ports for sensor cables, and it sent data remotely via the cellular network without a physical phone. The device had 5 ports for temperature sensor cables, giving it the ability to monitor multiple cookstoves in a single home, including the traditional cookstove.

In cases where network connectivity was reliable, the StoveTrace 5 performed its function, sending cooking data to the StoveTrace dashboard where cooking could be viewed remotely by project stakeholders. However, both connectivity and the setup requirements made the ST5 challenging. Connectivity was spotty in more remote villages even when some cellular or GPRS coverage was present. Furthermore, SIM cards were sometimes removed from the devices. StoveTrace 5 also needed a power source, requiring sensor cables and wires to be run through participant households. Nexleaf’s field staff worked with engineers to enumerate all the problems, and it became clear that Nexleaf needed a device that could operate without being plugged in or relying on consistent network connectivity in every household.

These known issues with StoveTrace 5 inspired the next generation stove monitor which could operate in the more remote settings: without network connectivity and without power. The StoveTrace “Trek” borrowed from technology developed for Nexleaf’s vaccine transportation investigations. The Trek is a small data logger that runs on battery power and transfers data via a Bluetooth connection. The Trek enabled data to be stored in remote environments and to be collected during an in-person visit by a field agent using a smartphone or tablet. The smartphone then sends data once it is connected to a cellular network or wifi, allowing cooking to be remotely viewed in the same way as earlier versions, albeit only as “real time” as the frequency of collection.  

The Bluetooth-enabled Trek has been used on over 1,000 improved and traditional stoves since 2019. This Bluetooth system is far less intrusive to households and can be used anywhere, and while it requires an in-person visit, the Bluetooth enables the data to be downloaded without plugging in cables or using other physical means. Depending on the location of the stove, data can even be transferred without the data collector entering the house. The need for in-person data collection, however, makes the Bluetooth-based model practical only in settings where entrepreneurs or field agents are making frequent visits to the communities and households being monitored, or for short-term studies where frequent data collection is part of the plan. 

All iterations of Nexleaf’s IoT technology for stoves have encountered challenges inherent to monitoring stoves using external temperature sensors. Thermistors must be placed precisely in order for proper temperature readings to take place, involving customized attachments to secure the sensors and data loggers in place. As externally placed devices, households can easily move the sensors (and have to in order to maintain and clean their stoves), leading to inaccurate readings or missed cooking events. The temperature data itself has to be processed into cooking data, a source of variation and compromise to the reliability of the data since every household temperature pattern is different. 

What’s Next
Temperature monitoring will likely continue to be the best source of objective cooking data for the more basic improved biomass stoves. Technologies like Nexleaf’s ST Trek can enable unparalleled insight into cookstove use when the proper support (ability to perform in-person visits) is available. Modern energy and advanced biomass stoves offer more opportunities for IoT enablement and remote monitoring. Many companies are enabling IoT on liquid fuels such as LPG and biogas in order to enable mobile-based payments and pay-as-you-cook plans. These technologies therefore also create a valuable, objective form of usage data that is more direct than temperature. Electric appliances can utilize network-connected energy meters to monitor use, especially relevant as temperature sensors are difficult to attach to most electric cookers. Nexleaf has prototyped an electric version of the StoveTrace Trek which still uses the Bluetooth data transfer but logs amperage rather than temperature. Forced-draft biomass stoves may also be able to incorporate IoT-enabled fans and other components for direct monitoring. As cellular network access becomes more common, there will be fewer complications for network-connected monitoring systems. There are alternative low-power wireless cellular networks, such as LoRa and Sigfox, which have trade-offs in terms of required infrastructure, range, cost, availability, and battery life. We chose Bluetooth to explore aspects of these trade-offs in parts of the world that do not have reliable network coverage. Emerging IoT technologies may be able to benefit from the lessons learned through Trek and the possibilities opened up by Bluetooth.