Solar Air Heater - Part IV, DC-DC regulator and Arduino

To complete the air heater project, a thermostat is needed.

This thermostat needs to:

1. Measure temperatures in the garage, outside and inside the solar air heater.
2. Calculate whether the fan for the heater should turn on.
3. Be able to control the electric fan.
4. Be remotely inspected.

The decision came down to using the Arduino with an ethernet shield.

The current setup can be accessed by clicking on the Arduino link at the top of this page.

Here's a pic of the temperature sensor purchased from Jameco.

It has 3 leads (wires). Two are for power, a positive and a negative and the third outputs a voltage that is proportional to the temperature.

To the left is where 24V from the batteries is transformed to 12V for the Arduino and for the fan. In the middle is the fan. To the right is the Arduino board enclosure.

Here is the converterboard. From the left comes the power from the batteries at 24V of pressure. The only power that goes out in this picture is to the fan to the right. There is also a switch which connects to the converterboard's LM2678 chip.

Since there are 5 temperature sensors and 1 humidity sensor, each had its own ethernet cable hooked up to it with 3 of the 4 twisted pairs being used. This is the mess that ensued:

Tried soldering all the power and negative wires at a poor attempt to clean it up.

In the end it was all hooked up but the readings were incorrect.

One problem Nick discovered is with the Arduino board in conjunction with the ethernet shield.

The ethernet shield is also connected to analog0 and analog1 pins for the purposes of controlling a micro-SD card. Since there is no micro-SD card on our ethernet shield, it just messes up with the data gathering, so Nick bend those pins on the ethernet shield so they do not connect to the Arduino. Instead, the signal pins are put directly into the Arduino board for analog0 and analog1.

Additionally the signal wires were too easily distorted by outside influences, so some capacitors were added to prevent unwanted fluctuations.

Another issue was our 24V to 12V converter board frying. While we are re-designing it, we purchased a commercial model to run the whole shebang.

Consequently, we cannot control the fan with the Arduino for the time being.

Nick checking out the board and de-soldering the chip.

Fried chip next to a good chip.

Fried board with the main chip removed. The chip was located at the top right.

Here is the new setup, with much larger boxes for ease of use.

At the left is the 24V to 12V regulator.

To the right is the Arduino board and all the connections.

You can see the capacitors here which connect from each signal wire to the common ground (to the right).

To give an idea where all these sensors are consider the following pictures.

The "heater input" is connected to the analog0 pin on the Arduino board, aka A0. This is the duct where air from the garage enters the solar air heater to.. uh heat up. The wire runs along the top...

...and down and then to the duct.

A1 is the heater output. This is where the hot air is pulled out via the fan. That mount fan is scrap wood recycled.

A2 is near the door at around a 5 foot height and chills inside the white covered box at the bottom right.

Inside there is also the humidity sensor (to the left).

A3 is the garage temperature at around the center in the middle, above the garage door opener.

The outside temperature is inside a box that is located on the outside of the garage.

This location will change. It appears to receive a lot of heat from inside the garage through the metal conduit and thus distorts the real outside temperature. The wire goes to the top right corner area of the door.

Into this non-working light fixture.

A5 is the humidity sensor, located in the same box as A2, as seen above.