Testbeds are a key tool for evaluating and bench-marking IoT solutions. Several public testbeds are being run by institutions around the world. These are built with a variety of tools, and are typically “heavy” installations with dedicated wiring, hard installations, switches, servers, and a reservation and experiment management back-end. To complement those, we have taken the opposite, minimalistic, approach in designing the OpenTestBed. The OpenTestBed features all the tools necessary to build a testbed from off-the-shelf components such as Raspberry Pi single-board computers, OpenMote B low-power wireless devices, and glass domes. Each TestBox in the testbed connects to an MQTT broker over WiFi, no dedicated wiring or back-endis needed. The Inria-Paris OpenTestBed testbed of 80 motes has cost only 9,480 euros, and is open-access. The OpenTestBed is a fully open-source and open-hardware project, which several institutions have already adopted.