Project EigenCAM -  Open Source Smartphone-based Self-referencing Spectrometer
Channel: Project EigenCAM
Date: 2021-06-14

INTRODUCTION
Welcome to Project EigenCAM! My name is Chuong Tran and in this video I’ll give you a quick overview of the resources available on www.eigencam.com for you to learn and build your own Smartphone-based Self-referencing Spectrometer.

WHY USE A SELF-REFERENCING SPECTROMETER?
Wavelength accuracy of typical spectrometers must be calibrated in advance to establish the relation between the pixel number and the associated wavelength by means of a calibration lamp with known emission line wavelengths. In addition, a recalibration has to be performed periodically since the pixel number versus wavelength relation can change with ambient temperature variations, or disturbance to the optical configuration in front of the camera, or the variations of the auto-focusing lens position commonly occurs in smartphones. 

Given that this calibration procedure has to be performed off-line, it would be desirable to address the need for a smartphone-based optical spectrometer that has simultaneous self-referencing and spectrum measurement capabilities to achieve excellent wavelength reproducibility.  

A self-referencing spectrometer that simultaneously auto-calibrates and measures optical spectra of physical objects utilizing shared aperture as optical inputs. The concurrent measure and self-calibrate capabilities makes it possible as an attachment spectrometer on a mobile computing device without requiring an off-line calibration with an external reference light source. 

AIM OF PROJECT EIGENCAM
There is considerable prior art in the development and mechanism and operation of optical spectrometers, spectrophotometers, calorimeters, and the like devices for measuring the light wavelength that is reflected, transmitted or scattered from physical objects. However, none of these prior art addresses the need for a low-cost optical spectrometer using the camera in a mobile computing device that simultaneously self-referencing and measuring the optical spectrum of physical objects. 

It is therefore an aim of Project EigenCAM to provide a novel system that can simultaneously self-referencing and measuring spectral characteristics in real time with the use of software App for a mobile computing device to enhance the visual interpretation of the spectrum that will provide spectral wavelength information inexpensively.

FREE OPEN SOURCE SOFTWARE & HARDWARE DESIGNS RESOURCES
https://sites.google.com/view/eigencam-com/open-source?authuser=6

Project EigenCAM makes software available under the MIT License.  The optical prescriptions for the spectrometers are located in the Zemax webpage. The 3D printing models are in the Solidworks webpage. The light spectrum analysis codes are located under Matlab, iOS, or Android web pages accordingly.

Additional how-to videos are in progress and will be uploaded as available.

SpectraVu App
The light spectrum analysis app, SpectraVu, processes the following events: 
1. A spectra image is captured. 
2. The App auto selects the self-referencing light (SRL) spectrum region. 
3. Utilizing the calibration wavelengths of the SRL pre-stored in App calibration file, a regression method is used to generate a calibration polynomial transfer function. 
5. The App then auto selects the external illumination light (EIL) under test spectrum region. 
6. The App applies the calibration polynomial transfer function to the EIL under test spectrum to convert pixel indices to wavelengths measurement.

PROTYPE DEMO UNIT
I built the prototype in the video to fit a slip-on case for the iPhone 6s.  Basically you just build a spectrometer module and then make an adapter part to match up with your phone case camera window. For calibration you’ll have to enter in 3 reference wavelengths of the reference LED you’ve seen earlier in the video but it’s only a one time calibration.

EXAMPLE BILL-OF-MATERIALS FOR PROTYPE UNIT:  https://sites.google.com/view/eigencam-com/tutorials?authuser=6
spectrometer main body 2020 r2
air slit aperture
PCB-LED-Driver
iphone6-adapter-post-r1
filter-pinhole-carrier
referencing LED
pwb-button-battery-switch-assembly-r1
diffraction-grating-1000lp-per-mm
diffuser
mirror 10x10x2mm
grating-post-r1
lens f21mm

More details: https://sites.google.com/view/eigencam-com/home?authuser=6