We launched a Kickstarter to raise $8,000 to turn the colorimeter prototype into affordable colorimeter kits. If the Kickstarter is succesful, we will be able to purchase the assembled boards in enough quantities to sell the kit for $80. In the meantime, we will continue to add educational labs, update the software and add to the list of calibrated solutions.

A 1000 ppm solution of ammonia standard was purchased from Grainger (Cat # LC17940-1). 1 mL = 1 mg N (1000 ppm N) = 1.22 mg NH₃  (1220 ppm NH₃). An aliquot was diluted with distilled water (dH₂O) to a working stock of 10 ppm (1 mL in 100 mL) and 100 ppm (10 mL in 100 mL dH₂O). These were diluted with dH₂O futher to get the a range of ammonia levels up to 2.0 ppm N (2.44 ppm NH₃). 5 mL of each solution was transferred to a test tube and ammonia levels tested with the API freshwater ammonia test kit. The image below shows some of the solutions after approx. 5 mins when full color was developed. A control sample (dH₂O) was developed alongside the ammonia samples and this was used to calibrate the colorimeter. Absorbance of the resulting green color was measured with the red led and results plotted.

Tube 0 = dH20; 1 = 0.1ppm; 2 = 0.2 ppm, 3 = 0.3 ppm; 4 = 0.4 ppm; 5 = 0.5 ppm; 6 = 1.0 ppm; 7 = 2.0 ppm.

Redesigned the colorimeter LED and sensor PCBs to exchange the through hole terminal blocks for surface mount connectors. This will allow the boards to be mounted directly onto the enclosure walls.

Redesigned the Arduino shield board to a more simplified version. Shown on the left is an image of the new version 2.0 with an Arduino Uno.

Tartrazine (yellow food dye #5) has an absorbance in the 400-460 nm range with a peak absorbance of 425nm. A solution of tartrazine was diluted in water and absorbance values were measured using the colorimeter. An image of the result is shown on the far left. As expected, tartarazine absorbed light from the blue led (470 nm) but not red or green.

The same stock solution of tartrazine was diluted further to obtain a standard curve. Absorbance was measured at 470 nm using only the blue led. The linear relationship between absorbance and concentration is shown in the plot on the right.

The image on the left shows a plot of concentration versus absorbance measured with the colorimeter.

A series of dilutions of green dye was prepared from 0-100%  - the 10-90% dilutions are shown above. Absorbance was measured with the red led (625nm). The graph shows the linear relationship between absorbance and concentration. 

The first prototype of the Arduino Colorimeter shield is now in and we are currently testing the shield with the colorimeter. The shield provides a convenient way to connect the colorimeter to an Arduino Uno or Duemilanove. The colorimeter attaches to the shield via a ribbon cable between the 5x2 pin headers on the shield and the sensor board. In addition the shield provides connections for an LCD display, a potentiometer (display brightness) and a pushbutton for developing a standalone colorimeter.

The colorimeter sensor board was also modified to swap the 6x2 header for a 5x2 header. Design files for both the shield and the newer sensor version 1.1 can be found in the design files.

The original enclosure prototype was modified further to include a sliding cover and a cuvette holder. Below are some images of the new design.