I made a weather station to continuously monitor daylight and
temperature. Since the project is placed away from the house, it
is more convenient to use a battery to supply power, rather than
a long extension cord. During the day, the weather station
should run from a solar panel as much as possible to avoid
consuming the battery. And, rather than a person occasionally
checking on the battery levels and replacing the batteries, the
circuit should recharge the battery pack from excess solar
energy from the solar panel. This article describes the solar
and battery backup circuit, along with the recharging results so
far. Schematic of a simple solar-panel based circuit. A solar
panel is on the left side of the schematic. A diode (D1)
protects the target device against a negative voltage in case
the solar panel is installed in reverse. The diode is a Schottky
type (such as 1N5817) so that very little voltage is lost going
through it. The device itself contains the usual power supply
circuitry, such as capacitors