■ FIGURE 4
■ FIGURE 5
through coming out of the Master Control box and a six pin
high amperage connector for the Stepper motor power.
Internal connections are made using standard 0.1“ spacing
printed circuit board (PCB) headers and female connectors.
Everything is designed in a modular fashion for easy
repairs in the future. Connectors should be chosen for
easy disassembly and repair. Keep a log of all connections!
For example in this particular case, note the following:
unused I/O pins on the bottom of the Atom.
This project consists of many different circuits. The
stepper motor driver board was built using my own circuit
board design (Figure 4), however it is a simple circuit and
could just as easily be soldered onto a universal protoboard.
The MAX6675 SOIC (surface-mount chip) is mounted
to another circuit board I designed (Figure 5). An interface
board is needed to convert from surface-mount to
standard 0.1” spacing, and is available from epboard.com.
The clock, indoor temperature, outdoor temperature,
and Atom microprocessor are all mounted on universal
protoboards. These boards may be purchased in various
sizes and from many different vendors (see the Parts List).
Power for the entire project is provided by a computer
power supply seen in the lower right corner of (Figure 6).
It has plenty of amperage to drive the stepper motor and
run the microprocessor and associated sensors. It is
mounted directly inside the Master control box (Figure 6).
The end of the control box is cut out to allow access to
the power supply plug and fan openings (Figure 7). All extra
power output connectors are removed from the power
supply simply for aesthetics and space considerations.
Microprocessor Circuit Board
Atom pin 1 – DB-25 pin 10
DB25 pin 10 – Slave PCB pin 10 (connector 1)
Slave PCB pin 1 (connector 2) – LCD PCB pin 3
Using this method, in the future you can trace out
where the wires are going and what circuit goes through
which connector pin. All schematics use pin names that
correspond with the same pin names on other schematics.
All switches (both manual and limit switches) use
pull-down resistors. Connect one end of a switch to +5V
and the other side of the switch to the Atom pin which
already has the pull-down resistor installed on the PCB.
There are six manual switches and two limit switches.
Six manual switches are tied together in parallel for
placement in the master control box and the slave box
(three in each box).
The system may now be controlled
from two different locations. Limit switches
are used only for the stepper motor
travel limits. Note the following: The closed
limit switch CPU pin is shared with the
DS1620 outdoor temperature sensor reset
line. The DQ/DTA (I/O) pin 6 on the Atom
is shared by three components: indoor
temperature, outdoor temperature, and ■ FIGURE 6
the clock. There are four available
The Atom microprocessor (Figure 8) is mounted on a
universal protoboard. This allows you to swap out the board
for diagnostic testing. The board includes I/O connectors,
serial programming port, power input regulator, power
LED, and a reset pushbutton. Note that in the photograph,
the pull-down resistors for all switches are mounted
directly underneath the Atom itself. The schematic for the
Atom microprocessor board is shown in (Figure 9).
I used MAX6675 with a K type thermocouple,
purchased my sensor from VirtualVillage.com. Mount the
thermocouple assembly in a convenient location inside the
■ FIGURE 7
November 2008 37