January
2006, Issue 186
Electronic
Scarecrow
POWER
The
remote units are mounted away from any power sources,
so they have to be self-sufficient. The average power
consumption varies depending on which sensors are installed.
This varies from 170 ľA for the XY-axis accelerometer
up to 1,750 ľA for the e-field sensor.
A
set of eight AAA NiCd batteries supplies power with
a capacity of 240 mAh. This can run the system at 3.25
mA for three days, or longer, if less current is needed.
The batteries are charged from a photovoltaic array
made up of eight 3-V, 25-mA photovoltaic cells wired
in series/parallel for 12 V at 50 mA. The battery feeds
a low-power, 3-V regulator. A transistor acts as a 9-V
power switch.
