Handheld Scatterometer

=Problem Definition= We aim to design a self-contained, portable instrument for measuring and quantifying the turbidity of a solution over time by measuring the light scattered from the solution.

Background
Optical scatterometry (otherwise known as turbidimetry or nephelometry) is a common way to determine the concentration of a contaminant, such as bacteria or proteins, in a solution. The nephelometry method detects the concentration of the solution by analyzing the amount of light that is scattered 90° to a laser shined into the solution, while turbidimetry measures the concentration using detectors 180° from the laser. Nephelometry is better used for low concentrations, while turbidimetry is better suited for high concentrations. These techniques requires expensive machinery that is not always portable, or user friendly.



Specifications

 * Handheld
 * Touch Screen
 * Wireless Charging Battery
 * Durable
 * Production model Less than $200

Applications
Medical Clinics Fish and Wildlife
 * Point of Care: Negates need for central lab
 * Affodable/Portable: Use in small clinics or developing countries
 * On-site measurements: Stream/groundwater contaminant check
 * Ease of use: Minimal training required

=Design Considerations=

Initial Choices
For initial testing multiple PCB's are being used, one for each photodiode and for the laser diode, however, there are size constraints to consider and the three PCB's may be consolidated to one if it will save space.
 * Single PCB vs. Multiple PCB's

A laser module would be easier to install, because it has the lens built in, however the laser diode and external lens will have a greater degree of accuracy when installing.
 * Laser Module vs. Laser Diode and Lens

Final Decisions
Due to how small the PCB's are, the final design will not require the PCB's to be consolidated together as it does not save much space. Focusing a laser diode with a lens proved to be quite difficult, with not much benefit. For this reason the laser module was chosen for ease of use and compact design.
 * Multiple PCB's
 * Laser Module

=Project Learning=

PhotoDiode Amplification Circuit
In order to amplify the current provided by the photodiode, a logarithmic amplifier will be used in order to normalize the values given by the photodiode. The chosen Logarithmic amplifier is the Analog Devices ADL5303. Using the shown schematic a PCB was created. The photodiode that will be placed 90 degrees to the laser will have a higher linear amplification at the output of the logarithmic amplifier than the photodiode placed 180 degrees to the laser. This decision was made because of the little amount of light that it will be detecting. The final range of voltages for each photodiode range from 0.5V-2.36V for the 180 degree photodiode, and 1.4V-7V for the 90 degree photodiode.

Laser Diode Circuit
The laser diode needs an amplification circuit and protection circuit in order to drive the laser at a specified light and to protect the laser diode from being damaged due to over voltage or over current. The IC-WJ laser driver chip has been chosen due to its watchdog protection circuitry.

After much consideration, the team decided to go with a pre-built laser module with a built in lens. This would limit the amount of PCB's we would need to incorporate to the final design, as well as eliminate the need of calibrating a laser diode to a lens.

Cuvette Holder
The cuvette, which will hold the solution, will be placed in a 3D printed cuvette holder. The cuvette holder will have a hole in each side, to place 3 photodiodes and a laser diode into. All designs were done in TinkerCad. Several prototypes were made at University of Idaho facilities, before a final cuvette holder was printed from Shapeways. This design for a cuvette holder will be incorporated in the final design when a larger container will be 3D printed to hold all of the designed electronics.

Thermal Sensing
=Final Design=

Team Information
=Additional Documentation=

Project Planning

[Team Contract] [Product Requirements] [Project Schedule] [Budget]

Meeting Minutes

[September 11, 2018] [September 20, 2018] [September 27, 2018] [October 4, 2018] [October 11, 2018] [October 18, 2018] [October 25, 2018] [November 1, 2018] [November 8, 2018] [November 29, 2018] [January 17, 2019] [January 24, 2019] [February 7, 2019] [February 21, 2019] [February 28, 2019] [March 7, 2019]

Presentations

[Design Review] [Engineering Release Review]

Client Interview

[Interview September 27, 2018]