Energy harvesting from ambient radio frequency waves has the potential for realizing long lived wireless sensor networks, by reducing their dependence on the limited and irreplaceable on-board batteries. We propose two cross-layer approaches, called device-agnostic (DA) and device-specific (DS) protocols, for such networks composed of energy harvesting boards connected to off-the-shelf available sensors. These protocols determine the routing paths and the harvesting-transmission duty cycle at each hop under different conditions. The DA scheme relies purely on the local measurements on the harvesting capability of a node after the sensors are deployed, and is useful for single-flow networks. The DS scheme provides a joint hardware–software optimization by allowing the selection of the energy storing capacitor, apart from the route and duty cycle determination. Both schemes rely on a rich set of device-level experimental studies that help provide exact performance characteristics in practical scenarios, and results reveal significant performance improvement over other existing schemes.