#electrical subsystem

[biolight]

PCB and Octagon Walls

PCB attachment is a big part of our design. To make exchanging LED panels easy while maintaining a strong electrical connection, we designed an attachment system which uses male and female header pins (male pins on the PCB and female pins on the walls) and nails to secure the panels to the walls. Two panels (which are treated as one panel) are attached to each of the four opposing walls in the octagon. 

The image above shows a PCB attached to one wall next to our breadboard testing circuit and three protoboard proof of concept panels.

[biolight]

Making LED Panels

Our original plan was to make our led panels out of protoboards, but we've decided to switch to PCBs for a few reasons:

Etching the protoboard is time consuming. (The first try took ~5 hours and even after deciding to using wires to jump the space instead of the pre-connected paths production of each board still took almost two hours)

One of our major goals is ease of use---if these boards break and need to be replaced, we want something that is easy to make. The Huang Lab at Olin (who are getting our culture keeper at the end of the semester) already has PCBs designed for this purpose, so we've altered our attachment design a bit to be more compatible with their equipment.

Even though we're changing our design to fit PCBs, we're still making the four protoboards as proof of concept and to help demo and test our system. Time and budget constraints prevent us from ordering PCBs at this point since three of these boards (shown above on the right) cost around $100. 

[biolight]

Building the LED Panel

Today we started building the panels which will eventually be our LED lights. We're using double-sided, wired protoboards, which means we need to cut the wires on both sides of the board. To facilitate this, we marked which lines should be preserved in sharpie as well as where the resistors and header pins (for signal and ground) will go. In addition, we've marked where the octagon wall will need to be cut to make room for the female header pins and the wooden dowels (which will be used to secure the LED panels in a removable fashion). 

[biolight]

Designing the Protoboards

Now that we have the basic software working, we need to focus on manufacturing our protoboards to place on each wall of our inner octagon. One of our primary goals is to make these LED panels easily removable, so we have decided to use header pins as both a method of sending signal to our LEDs and fixing the panels to our walls in an easily removable and robust fashion, but first we need to determine the best place put them. We also need to determine how we are going to attach header pins to our wooden walls and where wires will be fed through the wall so that any changes that need to be made can be added to the CAD before our final cut sheet is submitted to the machine shop.  

The protoboards are actually smaller than the walls, as shown above, so we decided to place them on the lower portion of the walls in the interest of best light exposure to culture tubes. We had originally considered cutting up the protoboards to allow for a more even spread of light near the top of the box, but this made the manufacturing process difficult enough that the benefits did not outweigh the added complexity. Ultimately, the LEDs are spaced out evenly across board which is located in the lower two thirds of the octagon wall.

[biolight]

Software Integration

Our first significant software integration milestone has been reached! Today our electrical and software subsystem team combined working LED- and servo motor-control code into one copy of functional code which successfully controls all LEDs and motors simultaneously. Check out the functional system as shown in the video above!

[biolight]

Controlling 4 Servos with a Button

Up until now, we've been focused on controlling out LEDs and haven't given much thought to the mechanical control portion of our software. We're starting to build our first prototype soon though, so we needed to put together a basic method for controlling our 4 servos in order to open and close the four segments of outer box as discussed in this post.

We've succeeded in opening and closing all 4 servos in the correct order at the push of a button (critically separate from the computer-controlled portion for ease of use). The video shown above is a demo of this system working.  

Because the lid fits together like a puzzle, the order in which all the servos open is crucial. We can toggle the time delay between each servo opening once we're able to test the servos on our particle board prototype. Unfortunately, there is still a bug with using the button. In order to close the lid, the user must press and hold the button rather than pushing it once, which is likely due to the fact that we used delays instead of using a counter. We will be able to fix this bug by implementing a counter in later iterations of the code. 

After fixing this bug, we will integrate the arduino code for servo and LED control followed by development of a basic GUI. 

[biolight]

User Control of Intensities of Individual LEDs

Today we've finished our first major code deliverable for the project. We can now control four panels of light simultaneously and independently, which we do using a serial connection from python to the Arduino. 

Our next steps for software development will involve servo control, then switching panel sets (since we're working with 8 panels but only four will be used at a time), GUI design, and finally web interface.

[biolight]

Materials

This week we were able to acquire all of the materials needed for our first prototype. They are listed below:

protoboards (9)

LEDs (50)

9V Wall Power supply (1)

Arduino WiFi Shield  (1)

Particle board (2'x1'x1/4") (10)