Layout of Battery Charging Circuit
The second method of power storage used was a circuit that charged a nickel metal
hydride button cell battery. Nickel Metal Hydride batteries were used because they have a very
high charge density and unlike a lithium ion battery they do not require any type of charge
controller or voltage regulator to be incorporated into the circuitry. The circuit constructed to
charge the battery was very simple, it consisted of a full wave rectifier, capacitor and the battery
intended to be charged, as shown in Figure 7. The voltage produced by the PZT was first full
wave rectified then accumulated in a large capacitor, typically greater than 1000μF, then the
battery intended to be charged was placed in parallel with the capacitor. The simplicity of this
circuit allows it to be constructed very compactly and without additional components that would
result in additional power dissipation, as shown in Figure 8