emulate a metameric
Three possible CMOS
chips that could handle
our digital neuromere
• CD4049 — Hex
Inverting Buffer — six
inverting (e.g., IN low,
OUT high) buffers.
• CD4011 — Quad
NAND Gate — four NAND
(e.g., IN low + low; OUT
• CD4066 — Quad
Bilateral Switch — four
controlled by pins (e.g.,
pin to VDD, closed).
While each of these
CMOS ICs are very
reasonable in cost, when
the number of support
components for each chip
is factored in, the ideal
candidate is the CD4011
quad NAND gate. Remarkably, the CD4011 IC is also able
to handle all of our sensory input requirements, as well as
play nicely with a gutsy seven-transistor motor H-bridge (a
circuit that is based on a Mark Tilden design).
In spite of this easy IC choice, it still took several
iterations of the Microcerebrum design to get everything
right (see Figure 4). Additionally, even though this is
supposed to be a robot brain, the final version 1.0 printed
circuit board in Figure 5 includes an image of a
grasshopper on its bottom layer.
A lot of testing was performed on the
“proof-of-concept” board (see Figure 6). During
this testing, a major change was made to the
connections between the CD4011 ICs and the
H-bridge outputs. In order to maintain a
reasonable amount of flexibility with
Microcerebrum for controlling a robot, header
pins are used for every CD4011 output.
Therefore, female-to-female jumper wires can be
used for altering the behavior of these outputs
(see Figure 7). In the final tally, there are six
sensory inputs that are channeled through the
three CD4011 ICs (four visual inputs and two
tactile inputs); the resulting outputs (as shown
in Figure 8) are open for inserting jumper wires
to the two H-bridge motor drivers.
As you look through the Parts List for
Microcerebrum, there are three items that stand out as
oddball components that not every robot builder might
have laying around the workbench. Well, actually, two of
the items are very similar — the red and green LEDs. These
SERVO 11.2015 43
Figure 4. The evolution of Microcerebrum —
from the "proof-of-concept" at the top,
to version 1.0 at the bottom.
Figure 5. Two sides to Microcerebrum: left brain versus right brain?
Figure 6. Testing the