In this column, Tim answers questions about
all aspects of electronics, including computer
hardware, software, circuits, electronic theory,
troubleshooting, and anything else of interest to
the hobbyist. Feel free to participate with your
questions, comments, or suggestions. Send all
questions and comments to: Q&A@nutsvolts.com.
■ WITH TIM BROWN Q & A
Post comments on this article at www.nutsvolts.
• Question on R/C Robot
• Free to Air Satellite TV
• Testing GFCIs Properly
Question about a Previous Q&A
Question (R/C Robot)
QIn reference to Figures 3 and 4 of the November 2013 Q & A (page 22), there were three different answers to my question: (1) Using the Actiontec TV wireless HDMT kit; ( 2) Using
the data channels from a 27 MHz citizen’s band (CB)
radio; and ( 3) Using the New Zealand module. I am
wishing to go with using the data channels from the
27 MHz CB radio. To do this, I am assuming that I will
follow Figure 4 from the November 2013 issue, with four
CB radios, two transmitters, and two receivers.
However, I am confused on how to access these data
channels on the citizen's band radios. As a reminder, I am
building a robot, using two Raspberry Pis: the first one
being the robot's brain; and the second being the base
unit, controlling and monitoring the robot, with
communication to each other up to 1,000 yards.
Would you please give me an idea of which CB radios
would have these data channels, and how to design these
two circuits to access the data channels? I am also
assuming that I will be needing two CBs for the robot,
connecting one as the transmitter to pin 26 (GP- 7) and the
other as the receiver to pin 5 (GP- 3) on the Raspberry Pi,
then two more radios for the base unit, connecting one as
a transmitter to pin 3 (GP- 2) and the other as the receiver
to pin 26 (GP- 7) on the Pi.
— Timothy Harner, Monticello, UT
AI am including Figure 4 for reference. The FMT 2712 and FMR 05D are modular FM transmitters and receivers, respectively, operating in the 27 MHz range, made by Elsema for radio
control (R/C) hobbyist projects such as aircraft or cars, so
using them with a robot is an excellent application. The
connections to the Raspberry Pi appear correct since the
general-purpose Input/Output (GPIO) can be used with
the + 5 volt signals to and from the modules. The Pi's
GPIO are unbuffered and unprotected, so I would
recommend optical isolators to prevent "fried" Pi (pun
This project will require two FMT 2712s and two FMR
05Ds, with each set on a different frequency such as
27.045 and 27.145 MHz for full duplex operation
(communications in both directions simultaneously).
The "big" deal in this project is to program the Raspberry
Pi to perform the command operations.
Also be sure to encode your signals with a code
header that identifies your signals exclusively to prevent
interference with CB radios, garage door openers, and
R/C hobby devices (you may need to experiment with the
frequencies based on the local channel usage).
This project has a special appeal to me since I taught
robotics at a community college, but only got to work
with the industrial models — not the fun stuff like your
project. If you are building a flying robot, be sure to check
with local and Federal Aviation Administration (FAA)
regulations, which at present are very fluid.
8 January 2015
■ FIGURE 4.