Beginner’s Robotics on $50 a Month
Pin on DB25 Male
Connector
Signal Header Pin Wire Color
Pin on AVR
Mega 48
18-25 (ground)
11 (busy)
5 (D3)
4 (D2)
2 (D0)
GND 1 Black
MISO 2 Green
CLOCK 3 Red
RESET 4 Yellow
MOSI 5 Blue
TABLE 2. Programming Cable Connections.
10
18
19
1
17
and solder it so that it looks like Figure 3.
You will probably have to make several
tries to get the joints between the capacitor leads and the motor case to hold.
Just take your time and don’t give up.
Repeat this process for the other
motor.
outer cover ends on both
ends. On the end with
1-1/2 inches of the cover
removed, trim the blue,
yellow, and red wires so
that only an inch of each of
them is exposed. Strip one
half inch of insulation from both ends
of all the wires so that the cable looks
like Figure 5.
The resistors and the pin jumpers
will be added inside the connector
hood. Because of the short distances
involved, it will be easier to make
jumpers out of leads trimmed off of
components than out of the hookup
wire. You will have to take your time
while doing this to make sure that
everything fits. Read the rest of this
subsection several times and lay the
pieces out to make sure that you
understand how everything fits before
you start cutting.
Take three 360 ohm resistors and
trim their leads so that only 8 mm (a little more than a quarter of an inch) is
left on each end. Save the pieces you
trimmed off. The solder cups on the
DB25 connector have numbers next to
them. Solder one end of one of the
trimmed resistors into the solder cup
for pin 2 (don’t forget the rosin paste).
Do the same thing with another
FIGURE 4.
Programming
Circuit
Schematic.
Making the Programming Cable
The simple cable programmer you
will be making is based on a design
originally in Sample Electronics which is
also described on the Dontronics website at www.dontronics.com/dt006_
programming.html
The only differences between this
cable and the one on the Dontronics
site are the pinout on the end that will
connect to the bot and the size of the
resistors. Figure 4 and Table 2 show the
connections. Note that pin 18, 19, 20,
21, 22, 23, 24, and 25 of the DB25
male connector must be connected to
each other. To protect your computer’s
printer port, 360 ohm resistors have
been added in series with the MOSI,
RESET, and CLOCK signals.
Cut a four-foot piece of the six
conductor cable. Cut off one inch of
the outside cover from one end of the
cable and 1-1/2 inches of the outside
cover from the other end. Trim the
white wire so that it ends where the
resistor in the cup for pin 4 and take
the third resistor and solder it into the
cup for pin 5.
Lay one of the pieces you trimmed
off of the resistors across the solder
cups for pins 18 to 25. Solder it to each
of these cups.
The DB25 hood came with several
pieces of hardware which are used to
secure the cable and hold the two
pieces of the hood together. The two
curved pieces of metal are called cable
clamps. Normally, they go around the
cable where it enters the hood with
their concave sides facing each other to
form a ring around the cable. However,
our cable is smaller so we will be
placing the two pieces around the cable
with the curved parts facing the same
way. Attach the cable clamps around
the cable at the end with the 1-1/2 inches of exposed wires as shown in Figure
6. You now need to solder the wires as
shown in the photo: the blue wire to
the resistor for pin 2, the yellow wire to
the resistor for pin 4, the red wire to the
FIGURE 5. Cable
With Ends Prepared.
FIGURE 6.
Programming Cable
With Hood Removed.
FIGURE 7.
Breadboard End
of Programming
Cable.
SERVO 01.2007 59
