st remove the laser cut pieces from the acrylic plate and remove the protection foils from both sides of all pieces.Then try to stick the pieces together, to ensure that all fits well. First connect the central elements with the back and front walls, then add the right and left side pieces. Now try to place this on the base plate and to stick the tongues into the holes of the base plate.They should fit perfectly, but there can be minimal differences in material thickness. So in case you may need to break the edges a bit with a file or sandpaper, just until the pieces fit. Now place the side walls of the cuvette chamber and make sure they fit as well. Now disassemble the pieces again.
As a next step assemble the sensor unit. Solder the header to the breakout, according to the instructions found at Adafruit ("Learn" on the product specific pages). Now fix the cables to the ports. Make sure to write down which cable is connected to which port (Gnd, Vin, SCL, SDA; LED).
Alternatively you may solder the cables directly to the soldering ports.
At next fix the breakout to the sensor holding plate using two 2.5M screws, nuts and washers. Depending on the sensor you are using, you may have to turn the sensor holding plate. Adjust in a way that the sensor chip is placed exactly behind the rectangular hole, then tighten the screws.
Now stick two nylon M3 screws through the holes in the inner wall element and at the distance piece. Then stick the sensor holding plate onto the screws, allign the placement of the rectangular holes and fix the position with two other nuts.
Now assemble the LED unit. Stick two Nylon M3 screws through the holes of the second inner wall element. Stack the three LED holder elements on the screws, then place the LED into the resulting central hole. Now add the LED fixing piece and fix the stack with two M3 nuts. Make sure that the LED is properly alligned before you tighten the nuts. Connect the cables to the LED. The longer wire is "plus", the shorter "ground". To check functionality and optimal allignment, connect the LED with your power source, in case adjust the allignment.
Now assemble the "photometer box" as you have done before. First run the cables through the holes in the back plate.Then stick the tongues of the two plates with sensor and LED into the holes of the back plate, add the front and side plates and place the box on the base plate.
I would recommend to place four small silicon rubber feet on the botton of the base plate.
!!! Do not glue the box, as you may not be able to disassemble it any more !!!
I recommend to fix the box it with a some adhesive tape, if required.The most recent, but yet-to-be-build layout will simplify assembly and fixation of the structure even further.
Finally assemble the lid. Glue the two pieces defining the lower edge to the lid plate. Then glue the handle to the center of the lid plate.To reduce reflection, you may add a piece of self-adhesive felt to the inner side of the lid.
Connect the cables to the corresponding ports of your breadboard, PI or Arduino and check for functionality of the sensor and LED.
Step 3: Setting Up the Raspberry Pi; Required Software
As both sensors are communicating via I2C, you will have to activate this on your Raspberry. In addition you may need to install the appropriate drivers/kernel support. As you can find very good and detailed instructions on this at the Adafruit website (Adafruit: GPIO/I2C setup), I will not describe this here in any detail.
If you succesfully have implemented I2C on the Pi, connect the sensor with Ground, Vin (I use 3.3V) SDA and SCL. In the case of the RGB sensor you also need to turn off the build-in LED by connecting the LED line with Ground. Check if the sensor can be found by entering "sudo i2cdetect -y 1" at the shell.
Unfortunatelly both sensors are using the same I2C adress, 0x29, so you can't use them in paralell.
Now you need to install some software to perform your measurements. Luckily Python programs to read the data from the sensors were already available, so I only had to modify the TCS34725