S.N.A.K.E.: A Dynamically Reconfigurable Artificial Sensate Skin ...

whisker is epoxied to the package of the sensor. For this to be possible the whiskers have to
strain the package enough for the sensor to respond, which is easily obtained if the whiskers
are thick and stiff enough, and enough gain is given to the amplifier.
The circuit necessary for its signal conditioning depends directly on the type of information
that is desired. Vibration, strain, shock or simply activity can all be derived from this sort
of sensor depending on the signal conditioning and sampling chosen. A very detailed review
of possible circuit options are shown in the Measurement Specialties Piezo Film Technical
Manual [63]. Since the idea of including whiskers was mainly to detect the presence of
close activity, a very simple circuit was used to generate vibration pulses, which are then
connected to an input pin of the microcontroller, which can then either extract the vibration
frequency, or simply report if there was or no activity for a certain period of time. This is
also shown in Appendix C.
Ambient Light
Although one might not notice the fact that our skin is indeed capable of sensing ambient
light, this becomes clear if we take into consideration that it is light and not heat which
causes the familiar melanin concentration change in the skin when we spend long times
under the sun; in other words we get tanned because of the amount of light received by our
skin. Some animals (e.g. Cattlefish have optical sensors distributed in their skin).
Including an ambient light sensor into the nodes would allow several applications to be
developed with the network. Some possibilities include the retina-like light edge detection
system presented by Lifton in his push-pin distributed-computing-platform [39], and light
gradient and source direction detection, and longrange proximity detection by cast shadows.
This capability was implemented by adding a Toshiba TPS851/52 ambient light sensor,
shown in Figure 3-19. This tiny device was created as an illuminance sensor for brightness
control of mobile device displays, and it is based on a current-amplified photodiode. It is an
ideal option for the Skin Nodes because it doesn’t need any external amplification, which
reduces component count. It also has a low supply-voltage and power consumption that
70