from a wide variety of colors, but to minimize color artefacts I would recommend black, grey or white.You can find the SVG-file defining the latest tested version at a later step of this instructible.
- a sensor breakout:
* For the colorimeter, the TCS34725 RGBW-sensor breakout from Adafruit (< 8 US$/€, www.adafruit.com/products/1334) is used.
* For the photometer I use the TSL2591 breakout from Adafruit (< 7 US$/€, www.adafruit.com/products/1334) .
I ordered both breakouts at Flikto, Germany.
- a light source:
* For the colorimeter I am using a 5 mm naturally white LED with a narrow emission angle (Nichia NSPW500DS, about 2,20 € at Conrad, Germany). Please be aware that a "white" LED does not give a homogenous emission spectrum, as sun light, but a sharp blue peak and a bell-shaped emission spectrum with a maximum in the yellow-green range (see image). "Naturally white" LEDs emit similar amounts of light in the red, green and blue regions.
* For the photometer, a 5 mm LED with a color optimal for the specific analyte shall be used.
E.g. for a dark red analyte, you may use a green LED, a yellow LED for a blue dye.
You can find an overview of some commercially available LEDs with different colors at a later step.
The 5 mm LEDs can be powered either by a two 1.5 V batteries or using the 3.3 V output of the Raspberry Pi. Most yellow, orange and red LEDs will need a series resistor (e.g. 60 Ohm) to reduce the voltage to 2.1 V.
In addition to the above, an assortment of screws, nuts and washers (2.5 M and 3 M), silicon rubber feet and some cables are required. I also would recommend to use a breadboard to connect RPi and device.
A more detailed list is found at a later step.
Step 2: Assembly of the Device
The parts for the housing are constructed in a way that they fix together precisely, with grooves and tongues, without gluing. Only the assembly of the lid requires a bit of glue.
The pictures shown here may not represent the latest version of the device, as its layout still is subject of ongoing optimization.
At first 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 al