Abstract
We present a datalogger based on Arduino cards and commercially available tools for radio frequency identification, which we term the e-RFIDuino. Designed to be robut, easy to build and install, it detects and records the mobility of objects tagged with active transponders emitting in the ultra-high frequency domain (433.5 MHz). It functions without connection to the power supply network and is adapted to harsh outdoor environments. Once installed in the field and its on-site sensing field is determined, the data collected (timestamp of detection, transponder identification number, and received signal strength indication) allow estimation of the virtual velocity of tracer passage and investigation of displacement patterns at the scale of the area of detection. Experimental tests showed the device to have very high effectiveness when used to monitor the passage of sediment tracers in a torrential river system during various flood events over several months. The total cost to construct this open source device is below 850 Euros, and it is easily customizable. In the future, it could be equipped with a system for data transmission over the mobile telephone network to reduce the field effort and time required to obtain data, and to provide real-time triggering of field acquisitions at the most appropriate times.