Nuts and Volts - November 2010

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

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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