A PCB Based Sap Flux Sensor for Increased Manufacturability and Lower Cost

Sap flux probes have been used to study sap velocity since the early 20th century and have progressively improved in accuracy and usability. Advances are also being made in making these devices cheaper via open-sourced approaches; however, existing solutions require extensive time and skill to construct a reliable device. When our lab tried to replicate earlier open-source designs, only two of the first ten probes built passed rudimentary testing. We therefore redesigned the system and discovered a printed circuit board based design that simplifies construction and presents opportunity for automated mass manufacturability at a scale not possible with existing designs. We present new designs for both the thermal dissipation method and the heat ratio method were tested. These new open-source designs for wireless sap flux probes communicate over 2km using the LoRa protocol to an internet hub, where data is logged in near-real-time and is accessible online.