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by
Dennis Clark
Q. Every once in a while there is a question floated
around in my local robotics group that (I think) is
such an epiphany (read: slap forehead) that I think
it deserves a wider audience. This first question is one of
this nature:
Does anyone have any recommendations for an
inexpensive DC-DC converter that has 11-14 VDC in, 5 VDC
out (up to 3-5 amps)? I need a heftier supply for the low-level control system on my robot. Currently, I’ve got a 12V,
12 Ah lead-acid battery with a 5V-1A converter, and I’m
reaching the limit of the converter when I add my sonars
and IRs ... later, I would prefer an off-the-shelf solution.
— Daniel Herrington
A. My first thought was the TI PT78ST105, which is a
1.5 amp 5V switching regulator that works with up to
38V. This nifty part has the same pin-out as the
venerable 7805 regulator and is way more efficient.
Another suggestion was the TI PTN78020 which has similar
input voltage maximums and a 6 amp output with high
efficiency since it too is a switching DC/DC converter.
However, this part has lots more pins; it still needs no
external components. These parts are easily found at places
like Mouser, pricing depends upon various options. As good
though, as these solutions are, they are not “off-the-shelf”
and would need a circuit board to use. Don Clay put
forward the solution of using a BEC that the R/C airplane
hobby crowd commonly uses on electric aircraft that use
large battery voltages. This is a very cool idea because it
can be connected to the robot’s main battery and will
efficiently give the needed 5V in a small, self-contained
unit, and it already has easily usable cabling. The one that
Daniel selected was the Castle Creations CC BEC which sells
for about $22 at good ol’ Hobby Town USA (www.hobby
town.com); see Figure 1. This device is very useful because
it can be set to output voltages from 4.8V to 9V by using
the Castle USB link adapter (not included). In case you were
wondering, BEC stands for Battery Eliminator Circuit. In the
“old days,” electric R/C cars had a battery for the motor and
another for the R/C electronics. The BEC “eliminated” one
of those batteries.
Q. I want to send commands to my robot using an
IR remote. I don’t want to build another IR remote;
I want to use one of the bazillions that I have lying
around the house. How do I use these? How can I decode
their output?
— George S.
Figure 1. CC BEC.
A. Oh boy, I feel a marathon answer
coming up! I’m not going to go into
huge detail about every kind of IR
remote out there — there are a ton of web
pages that you can Google and find those
kinds of details. I’ll provide a selection of
them at the end of this answer for those
curious though. I did not find a lot of pages
that connected the dots between the various
formats and how to write a program to read
them, either. So, in this answer I’ll provide the
nitty gritty details of how the most popular IR
codes are created and provide some PIC code
that allows you to decode them. First, the
ugly details ...there are many, MANY different
16 SERVO 07.2008
