power failure. You do not
need to get fancy here; I
simply used an old battery
pack I had in my parts bin and
it has worked fine.
Crystal considerations for
the clock are important. Dallas
recommends various types of
crystals that will work with this
clock chip. I recommend you
follow the Dallas datasheet.
Dallas recommends a 32,768
kHz crystal with a 6 pF load
capacitance. Parallax sells a
compatible crystal and I have
listed the order number in the Parts List.
■ FIGURE 20
■ FIGURE 21
A 24 character by two line LCD display using the
Hitachi 44780 parallel standard was installed. The
serial-to-parallel driver chip for the LCD comes from
Kronos Robotics ( www.kronosrobotics.com) and is called
a Serial LCD 1 chip (Figure 21). I designed my own circuit
board for this chip, however I recommend you purchase
the Kronos LCD kit including the chip and PCB.
working control loop code. You can easily copy sections
from the main program ( woodstove.bs) — available on the
Nuts & Volts website — as needed for testing purposes.
After you have the control loop working and controlling
the wood stove’s exhaust damper, add in the extra
features such as temperature and data log code. A master
and slave control box is not strictly necessary either, but it
is here if you need it!
Help is only an email away. I encourage anyone with
problems to write me with any questions they may have at
This project was considerably more involved then I
originally expected. Many bugs in the software and
hardware problems occurred, actually too numerous to
I advise anyone building this project to start off
simple. Start off by breadboarding everything you can and
get the hardware and software operating on the bench
top first. For example, get your stepper motor and control
board working, then get the MAX6675 and thermocouple
working. Next, put both pieces together and write some
ITEM SUPPLIER WEBSITE PART
Atom 24 pin CPU http://BasicMicro.Com B0017
Dallas Maxim ICs www.maxim-ic.com/ DS1302,
LCD 24 x 2
November 2008 41