PTPM Energy Scavenger is envisioned as module that can harvest environmental energy from wide range of sources. To bring this concept to life versatile IC solution is needed. One such is Linear technology LTC3331, energy harvesting PMIC that can harvest energy from photovoltaic cells, TEGs, Piezoelectric elements and induction generators. Harvested energy is stored in on-board supercapacitors or external(optional) li-ion battery. Module can be divided into four parts:

• Energy harvesting input(AC1, AC2): Internally connected to low voltage drop full bridge rectifier and step-up/down switching converters.
• Energy storage - optional(BAT) and on-board (C10, C9): External battery can be used for high power consumption applications or if not needed it can be excluded to save on cost and space.
• Output voltage selection(S1): SPDT switch for adjusting output voltage from 1.8V to 5V.
• Output power supply(P1): Pin header with two Vout and two Gnd pins.

Resistor R1 is used to adjust battery charging current. Equation for calculating charging current is:  Icharge = 1.6 / (R1+60). Charging current should be in relation to average available harvestable energy in surrounding environment.

Main goal while designing PCB was to achieve smallest size as possible to reduce the cost of fabrication while still being relatively easy to assemble. PCB is 25x30mm in size so that it can be laid over li-po battery of same dimensions. PCB can be secured with two 1.8mm screws or with double-sided tape. Bottom picture shows fabricated PCB (bottom and top side):