the IR energy the same way. For
instance, a black dog’s hair will reflect
very little energy back, while a white
dog’s hair will reflect much more.
After experimenting with this type
of sensor, I again decided to look at
other prospects.
Sonar Sensor
■ FIGURE 4
■ FIGURE 5
I have used several sonar sensors
in the past and have had good results
with them. The problem is that the
sensors have a very wide angle of detection. The folks at
MaxBotix have come up with a line of ultrasonic range
finders. They all use a single transducer so the size of
these sensors is quite small. This single transducer
configuration also helps keep the price down. You can
review all the performance data for the complete line of
sensors on their website at www.maxbotix.com/
Performance_Data.html.
For this application, I found the EZ4 shown in Figure 4
is a perfect match (I’ve also used the EZ3 with great
success). The EZ4 gives you the ability to shut it down
using a control lead. This is important when using multiple
sensors.
The EZ4 has four data interfaces, which makes it easy
to measure its detected target distance. It will emit a pulse
width proportional to distance, talk to you in 9600 baud
serial (TTL inverted and requires decoding), generate an
analog voltage (also proportional to distance) and finally,
you can manually control the sensor element itself
through the “ping” interface. We will use the analog
interface in this project as it’s my favorite.
• STEP 1
The Perseus Carrier 1 kit you need to build for this
project comes with complete instructions. It is available
from Kronos Robotics. Make sure you don’t install the two
headers, though. When complete, it should look like the
carrier shown in Figure 6. The cost of the Perseus Carrier
1 is only $6. If you want to experiment using a breadboard, I recommend that you purchase two carriers so
that you will have one to play with outside the project.
You can simply plug the Perseus into whichever carrier
you are working on.
Perseus Microcontroller
• STEP 2
You will need to purchase a 7805 regulator and a
couple of headers for the carrier. (This is also available for
purchase as Option 1.) Attach a two-pin header to the
carrier as shown in Figure 7. This allows you to jumper the
regulator. Since we will always be using the regulator on
this project, you can simply solder a wire in place of this
header. If you do use the header, you will need to place a
jumper across the two pins.
To monitor the two sensors, I will be using
a Perseus microcontroller and Perseus Carrier 1.
Shown in Figure 5, this is a very small and
inexpensive controller. To program the
controller, all that is needed is a $10 EZRS232
driver and free software.
The carrier board (also shown in Figure 5)
has a tiny prototyping feature that will allow for
easy hookup of our sensors. This carrier also
has the ability to add a 7805 voltage regulator
to make powering our project very easy.
Perseus Construction
I am going to take you step-by-step through
the construction process. I will start with the
microcontroller, then show you how to build
the main stand for the project. Schematic 1
shows the completed hookup so that you can
troubleshoot in case you have problems.
■ SCHEMATIC 1
December 2008 41
