Q&A
■ WITH RUSSELL KINCAID
In this column, I answer 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
WHAT’S UP:
Join us as we delve into the
basics of electronics as applied
to every day problems, like:
Seven-Segment LED Help ✓
● LED Flasher and Beeper
Attic Fan Control
✓
✓
ATTIC FAN CONTROL
QI have two separate attic exhaust fans (they run on 110 volts AC). Each fan has its own thermostat. The
thermostats are very inaccurate and
difficult to synchronize. I would like
to set up a single, more accurate
thermostat that would control both
fans so that they will turn on and off
at the same time. I have thought of
using a furnace thermostat and some
sort of relay, but I am not sure how
to set this up. Can you make any
suggestions?
— Guy Fischetti
AHome thermostats are designed for 24 VAC and low current, so you will need a relay (see Figure 1).
In the parts list, the transformer has
quick-connect terminals (faston), but
you can find similar transformers at
the local hardware store. I would not
buy the universal 240/120 VAC type
because the wire is smaller and less
reliable. The thermostat will also be
available at the hardware store; the
round Honeywell type is what I have
in mind. The Panasonic relay can be
mounted with two screws on any flat
surface and the contacts are quick-connect terminals.
MICRO HELP
QI have a piece of equipment that uses a Motorola 68HC711E9 micro which has some
programming burned in. I want to
copy out the program and purchase
a few of these (getting almost
extinct) ICs and burn a few spares.
I’ve looked at some stuff on the
market but I’d like some help if you
don’t mind; I want to keep it simple
and cheap but accomplish the task.
Thank you in advance for some
advice/help.
— Michael Shelton
AI am an analog engineer; I would expect you to know more about this than me. However, I looked up the
datasheet and see that there is no
provision for copy protection, so it
should be easy. I found the EVB
Plus2 development board for $189
that should do the job. If you can
program an EPROM, the info at
www.dataman.com/WebPages/Supp
ort/S4/SupportS4Programming The6
8HC711.aspx should be helpful.
Feedback from Michael: I did
■ FIGURE 1
24
November 2010