sent to the “Display.c” code for (U2). “Display.c” takes the
temperature data and displays it on the quad seven
segment LED display. Four LEDS of different colors indicate
which temperature is being displayed. The three other LEDS
indicate an “active pump,” “power”, and “pump running for
freeze protection.” Again, all program listings are available
from the Nuts & Volts website.
In order to have a controller that could be easily
installed, I opted for a PVC junction box from a local home
improvement store. See Figure 2 for the large component
placement. The 9V power block was modified slightly by
soldering wires to the AC prongs and using shrink tubing.
The block is then bonded into the box using RTV rubber
cement (GOOP). The solid-state relay is fastened to the
box bottom with 6-32 hardware. The fuse holder F1 is
mounted in the box and F2 is on pig tails and stuffed
into the box.
Use care when installing the front panel with the PCB
attached, as there is not much clearance left. The box is
only a 4” x 4” x 2” and, in hindsight, a 5” x 5” board would
have been easier. The fuse holders and power block (PS1)
are from RadioShack. All the other components are from
Digi-Key. The solid-state relay (Q10) is from All Electronics.
For the future, I would like to add a data logger that will
put the temperature readings onto a Flash drive. Then I
could load the data into Excel and make a chart of the
results. Currently, I am reading these data manually with
four hour readings and a clip board. I’m looking to use the
PIC16F877 for this upgrade, but not sure something that
powerful is required.
Maybe I can think of something else for it to do, like
monitor solar intensity for calculations on a photovoltaic
system to run the pump. That way, I will have totally free
hot water. NV
For more information on this exciting subject, see our section
in the book store on Page 97 or the website on GREEN POWER.
August 2007 63