■ PHOTO 3. To test the voltage supplied to the circuit, I connected a
voltmeter to the rightmost and leftmost terminals of the battery. The
voltage supplied by the five potted plants was around 3. 2 volts in
■ PHOTO 5. The “crassula arborescens”
plant exhibits very good bioelectric
properties. Every ‘single cell’ of the plant
battery is able to supply up to 800
millivolts in open circuit. Connecting
more cells in series will increase the
■ PHOTO 4. The LCD timer running solely with the energy supplied by the
plants. Most of the time, the microcontroller is in deep sleep mode and
wakes up every second only to update the LCD display.
terminal is in contact with the pot soil. A relatively long
metal rod stuck into the dirt — also connected with an
alligator clip — is sufficient for this purpose (Photo 2).
Five potted plants are connected together in this way
to build a series circuit like the one shown in Photo 3. The
voltage supplied is around 3. 2 volts in open circuit. Now,
the MSP430 LCD timer with ultra-low power consumption
can be connected to the outer terminals of this battery.
The positive terminal of the LCD timer is connected to a
free branch of the first plant in the series, while the
negative terminal is connected to the soil of the last plant in
the series. As soon as the power is connected, the LCD
timer starts counting up from zero to nine every second
over and over again (see Photo 4).
Good for the Environment
Most remote environmental sensing networks
(for climatic and wildlife monitoring) rely on batteries
which must be maintained and replaced on a regular
basis. These networks would benefit from self-sustaining
power sources. By using the bioelectric properties of living
plants, it is possible to tap a natural source of energy to
power electronic circuits, thus eliminating the need for
foster the development of new applications for electronics
and expand the number of locations in which they
operate. As an example, Voltree Power (www.voltree
power.com) is now deploying the first applications of this
novel technology from forest fire detection and prediction
to agricultural monitoring using ultra-low power wireless
mesh networks with built-in sensors.
The Perfect Plant
It is well known that during Thomas A. Edison’s process
of inventing the incandescent light bulb, he and his team
travelled around the world to find the right kind of filament.
He tried thousands of different ones and sometimes exotic
materials until he discovered exactly what he needed. Well,
I almost had the same experience. Not all plants exhibit the
same bioelectric properties. I put different kinds of office
and house plants under test until I found the right one for
my project. Its scientific name is ‘crassula arborescens’
and it’s originally from South Africa. Fortunately, it is quite
common and very easy to find in any flower shop.
Most office and house plants supply a voltage in the
range of 200 mV to 400 mV, but our succulent plant is
able to supply up to 800 mV in open circuit as shown in
Photo 5. This is ideal since it reduces the number of
September 2010 37