FIGURE 17. Schematic of
the shift registers and
Quad Half H Bridges.
P2. “P” stands for
power. These last
two columns are
the power buss.
Note: Some breadboards need a lead
wire to connect the
columns at the mid
point and some do
not. It is always
best to check it
with an ohmmeter
to be sure whether
or not it is connected throughout. The
breadboard I used
for this project does
not connect all the
way through so I
had to add jumper
lead wires from row
G25 to row G26 in
columns 1 and 2 —
the first two
columns. I added
jumpers on P25 and P26, as well.
Cabinet Hinge
Mount the cabinet hinge on the
bottom of the project box (see Figure
14) if you have a project box that does
not come with hinges. Close the box
and place the hinge centered between
the top and the bottom. Mark the
holes and then drill making sure the bit
is small enough for the self-tapping
screws to hold the hinge in place.
top of the robot so if something goes
wrong, it is easy to “kill” the program
or power. Place the switch so that flipping it backwards puts it in the kill position. This way, when the robot is trying
to run away, you can hit the switch and
shut down the system. Hold the switch
up to the box where you want to
mount it and look to be sure it will fit
and that you can get the wires connected. Use the Dremel to cut a hole
for the switch in the top of the box as
described earlier. After cutting the
hole, place the switch in it and tighten
the mounting nut.
The kill switch
will be wired
between ground and the “enable
resistor” (EN on the schematic). The EN
is connected to the five-volt DC power
supply buss. On the schematic, there
are connections from the L293Ds
marked “EN.” These will all be wired
to row 58, column 1-4. In the “Go”
position, the H-bridges can drive
the motors. In the kill position, they
cannot.
Repeat this procedure for the
power switch on the side. You can
mount it in a different
location but be sure it
Kill Switch and
Power Switch
I mounted a
kill switch on top
of the project box
(see Figure 20).
I like to use
a toggle switch
with a one-inch or
longer toggle and
I feel it is important to put it on
FIGURE 18.
Terminal blocks.
Terminal Block -
From 1
From 2
From 3
From 4
From 5
From 6
From 7
From 8
From 9
From 10
From 11
From 12
From 13
From 14
From 15
Breadboard
to Row 1
to Row 6
to Row 9
to Row 9
to Row 6
to Row 17
to Row 20
to Row 20
to Row 17
to Row 40
to Row G1
to Row G1
to Row G1
to Row
to Row
FIGURE 19.
Terminal
block lead
wires chart.
Column 6
Column 3
Column 4
Column 7
Column 7
Column 3
Column 3
Column 10
Column 10
Column 1 (Use later)
Column G3
Column G2
Column G1
Column
Column
SERVO 01.2007 49
