Table of Contents
A review of the engineering requirements can be found under the 'Results' section of the following page:
An overview of the lessons learned can be found here:
Power ElectronicsThe power electronics are easy to setup up and are centralized around the solar charge controller. The controller has connection for the solar panel, 12V battery and load which are all clearly labeled. Wires from the +/- solar panel terminals are ran outside of the enclosure and can be connected to the solar panel. Currently the yellow wire is the positive and black is the negative. The 12V battery should be connected to with the proper polarization to the charge controller. There should also be a 15 or 20A fuse in line with the positive terminal of the battery. Currently the thick white gauge wire is connected to the positive terminal of the charger while the blue is connected to the negative terminal. Lastly the PCB and the solid state relay cube both need to be connected to the load terminals on the controller. From the PCB the white wire should go to the positive terminal and blue to the negative. For the SSR there should be a white wire from the positive load terminal on the charger that connects to terminal #2 of the SSR cube. There should then be another white wire from terminal #1 of the SSR which runs outside the enclosure and should connect to one side of the ink. There is another blue wire which connects to the other side of the ink and returns to the negative load terminal of the charger.
The control system is an easy to program, powerful 8-bit microcontroller chip from Atmel. Typical operation of the Arduino takes place an the Arduino Uno development board that allows the user to program the controller using a simple USB cable interfacing with the Arduino IDE on a computer. For our application, we wanted to use the chip in a standalone configuration on a PCB while still maintaining program-ability with the Arduino IDE and coding in C. This can easily be accomplished by removing the chip from the PCB and placing it back in the Uno development board. However, because the chip is in a DIP package, this takes additional time/tools and could result in the damage of one of the pins on the board. To over come this, pins on the development board are used in a breakout fashion and connected to the necessary pins on the chip while it is in the PCB socket. For this reason, a programming header is used on the board to easily mate with the pins from the development board. The Figures below show the programming header highlighted on the board and in the completed system:
To reprogram the chip without removing it from the board. We inserted wires into the development board and soldered them to a female header that can be inserted into the male headers on the PCB. With this complete all that needs to be done is to reconnect the development broad to the chip in the PCB via the header. Once this is complete, program-ability is once again possible. The figure below shows a subsystem testing image to insure that the chip could function in a standalone configuration. Wires from the Vcc, Gnd, Reset, RX, and TX are taken from the development board and attached to the corresponding pins on the chip in the bread board. This same configuration is captured on the PCB using the male headers and copper traces to the 28-DIP socket. The code used to program the board for the sysem to operate can be found here: System Control Code (To view, save the link as a .ino file and open in a code viewer like notepad++ or the Arduino IDE) The express PCB files for the PCB layout and Schematic can be found here:
Ink Layout and Testing
The ink layout was printed using a custom-made screen. The 12" by 12" layout was printed on a 14" square piece of glass. The vertical traces that connect the heating traces simulate nodes. The wire connections between the SSR Cube, the ink layout and the charger are explained in the power electronics section. Once the ink layout is attached to the system and current is sent through it, thermocouples can be attached to record the temperatures of the glass at various locations to map heat spread.
During heat testing on the current system, it was shown that the current copper-based ink is unable to withstand freezing temperature and begins to degrade rapidly under heating conditions. At room temperature, the ink heats substantially, but begins to burn when more than 6V of power is applied. At freezing temperatures, 12V was needed to create any change in temperature, but even at 12V of power, change in temperature was minimal. An improved ink is necessary to create an improved prototype.The detailed calculations for the ink layout and analysis can be found here:
Other notes on heat testing:
It would be best to try to find a better method of connecting the thermocouples to the glass rather than using painters tape. Painters tape doesn't provide for a secure connection, particularly at cold temperatures, and can lead to damage of the ink.