Gadget Freak Case #276: See UFOs and Explosives With a DIY Polarimetric Camera

It's no secret that there are entire wavelengths of light invisible to the human eye. Animals and insects have eyes that can filter light and polarize it to all sorts of benefits like seeing in the dark and hunting prey. For a more in-depth definition you should consult your old college physics book, but the idea of polarized light is that it oscillates on a single plane, as opposed to scattered around like normal sunlight or lamp light.

You've probably seen cameras use polarization filters to enhance or remove certain colors in a shot. But this is really only the tip of the iceberg. Long story short, if a human could see in polarized light he or she would be able to detect all sorts of things normally invisible to the naked eye.

Enter the polarimetric camera.

Design News reader David Prutchi has come up with a project - the DOLPi - an affordable, Raspberry Pi-based polarization camera that anyone can use to see polarized light. Aside from some interesting visuals you'll also gain the ability to detect unseen objects like pollutants and hidden explosive devices (if you're the sort of person concerned about that sort of thing...we don't judge).This project was a finalst in the 2015 Hack-A-Day competition.

Prutchi has included a whitepaper with highly detailed build instructions, a parts list, and Python source code to run the camera.

Watch the video below for an explanation of the DOLPi and to see it in action:

 

Download the full build instructions and parts list here

Want to submit your own project to Gadget Freak? Email us! Be sure to include "Gadget Freak" in the subject line.

As always, Gadget Freak is brought to you by Allied Electronics and Design News. You can recreate David Prutchi's gadget using the parts list below:

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DOLPI-UI PARTS LIST




Component reference Component/Material Source
RasPi Raspberry Pi 2 - Model B - ARMv7 with 1G RAM Allied Stock#: 70465426
SD Card SanDisk SAEMSD64GBU3 64GB
Extreme UHS-I microSDXC Memory Card (U3/Class 10)
B&H Photo
+5V Power Supply 5V 2A Switching Power Supply w/ 20AWG 6' MicroUSB Cable Adafruit ID: 1995
RasPi NoIR Camera Raspberry Pi NoIR Camera Board - Infrared-sensitive Camera Allied Stk #: 70323539
RasPi Touchscreen Pi Foundation PiTFT - 7" Touchscreen Display for Raspberry Pi Allied Stk #: 70689378
Keyboard/Mouse USB keyboard and mouse Allied Stock#: 70472529
USB cable USB male to USB micro male 6” cable
To connect Raspberry Pi to Pi Foundation PiTFT Touchscreen
Allied Stock#: 70591759
Lepton® Longwave Infrared (LWIR) Imager FLIR Lepton® Development Kit Sparkfun Part No. KIT-13233
Wires to connect FLIR Lepton®
Break-out board to Servo Hat
Premium Female/Female Jumper Wires - 40 x 12" (300mm) Adafruit ID: 793
EMI filter for Lepton® Fair-Rite P/N 0443164251/B1 Allied Stock#: R1057478
Servo Controller Adafruit 16-Channel PWM/Servo HAT for Raspberry Pi Adafruit ID: 2327
2 x Servos Two HiTec HS-322HD heavy-duty standard-size ±90⁰ hobby servos Jameco Part No. 395760
Optics

4 x Wire Grid Linear
Polarizer Film Filters
Four 14.5 mm x 14.5 mm filters cut from 80 mm x 50 mm Asahi KASEI wire-grid polarizing film sample. MeCan Imaging
RHCP and LHCP Circular
Polarizer Film Filters
RHCP and LHCP polarizer films taken from RealD 3D movie glasses RealD movie glasses
VIS Filter 1” diameter BG-39 glass filter Edmund Optics Catalog Number 48637
IR Filter 1” diameter optical-cast plastic IR filter Edmund Optics Catalog Number 43948
UV Filter 1” diameter BG-39 glass filter + 1” diameter UG-1 glass filter Edmund Optics Catalog Number 48637 + 46047
Filter Retention Rings Easy-Install Spiral Internal Retaining Ring,
Spring Steel, for 1" Diameter
McMaster-Carr Part Number 91663A570 (10 pack)
3D Printed Parts

Polarization Analyzer Filter Wheel 3D printed Polarization Analyzer Filter Wheel. Black PLA or ABS DIY using FilterWheelSquare.stl
Bandpass Selection Filter Wheel 3D printed Polarization Analyzer Filter Wheel.
Bandpass Selection Filter Wheel. Black PLA or ABS
DIY using FilterWheelCircle.stl
Light Shield Enclosure Section 3D printed Polarization Analyzer Filter Wheel.
Light Shield Enclosure Section. Black PLA or ABS
DIY using LightShieldFrame.stl
Enclosure Back 3D printed Polarization Analyzer Filter Wheel.
Enclosure Back. Black PLA or ABS
DIY using EnclosureBack.stl
Mechanical Hardware

Front Plate and Main Chassis Multipurpose 6061 Aluminum, Brushed Finish, 0.032" Thick. Front Plate and Main Chassis cut and drilled per templates Machined from one sheet of McMaster-Carr Part Number 1651T11
Tripod Mount Multipurpose 6061 Aluminum Rectangular Bar,
7/8" x 7/8" profile. Tripod mount machined per template.
Cut from McMaster-Carr Part Number 9008K13
4 x Chassis-to-Front Plate Standoffs Four Aluminum Male-Female Threaded Hex Standoff,
1/4" Hex, 7/8" Length, 4-40 Screw Size
McMaster-Carr Part Number 93505A445
4 x Chassis-to-Touchscreen Standoffs Four Aluminum Male-Female Threaded Hex Standoff,
1/4" Hex, 2" Length, 4-40 Screw Size
McMaster-Carr Part Number 93505A439
4 x Chassis-to-RasPi Standoffs Four Aluminum Male-Female Threaded Hex Standoff,
1/4" Hex, 9/32" Length, 4-40 Screw Size
McMaster-Carr Part Number 93505A476
4 x RasPi to Servo Hat Standoffs Four Aluminum Male-Female Threaded Hex Standoff,
1/4" Hex, 13/32" Length, 4-40 Screw Size
McMaster-Carr Part Number 93505A485
8 x Servo Standoffs Eight Aluminum Male-Female Threaded Hex Standoff,
1/4" Hex, 11/32" Length, 4-40 Screw Size
McMaster-Carr Part Number 93505A482
¼” 4-40 screws 18-8 Stainless Steel Pan Head Phillips Machine Screw,
4-40 Thread, 1/4" Length
McMaster-Carr Part Number 91772A106 (100 pack)
RasPi Standoff Screws 18-8 Stainless Steel Pan Head Phillips Machine Screw,
4-40 Thread, 3/16" Length
McMaster-Carr Part Number 91772A105 (100 pack)
4/40 nuts Type 18-8 Stainless Steel Hex Nut, 4-40 Thread Size,
1/4" Wide, 3/32" High
McMaster-Carr Part Number 91841A005 (100 pack)
LEPTON screws 18-8 Stainless Steel Flat Head Phillips Machine Screw,
1-72 Thread, 1" Length
McMaster-Carr Part Number 91771A175 (50 pack)
LEPTON nuts Low-Strength Steel Hex Nut, Zinc Plated,
1-72 Thread Size, 5/32" Wide, 3/64" High
McMaster-Carr Part Number 90480A002 (100 pack)
RasPi NoIR camera screws Nylon Pan Head Machine Screw, Phillips, 2-56 Thread, 1" Length McMaster-Carr Part Number 93135A019 (100 pack)
RasPi NoIR camera nuts and LEPTON spacers Nylon 6/6 Hex Nut, 2-56 Thread Size, 3/16" Wide, 1/16" High McMaster-Carr Part Number 94812A100 (100 pack)
Hub screws and nuts 0-80 Thread Size machine screws Ace Hardware
Miscellaneous

Glue White paper glue to retain polarizing film filters Office supplies store
Double-sided tape Heavy-duty double-sided tape to adhere EMI filter to Chassis plate Office supplies store
Adhesive tape ½” adhesive tape to tack front servo wire to Front Plate Office supplies store






DOLPI-EO Electro-Optic Polarimetric Camera




Component reference Component/Material Source
RasPi Raspberry Pi 2 - Model B - ARMv7 with 1G RAM Allied Stock#: 70465426
SD Card SanDisk SAEMSD64GBU3 64GB Extreme
UHS-I microSDXC Memory Card (U3/Class 10)
B&H Photo
+5V Power Supply 5V 2A Switching Power Supply w/ 20AWG 6' MicroUSB Cable Adafruit ID: 1995
RasPi Camera Raspberry Pi Camera Board Allied Stk #: 70280250
RasPi Touchscreen Pi Foundation PiTFT - 7" Touchscreen Display for Raspberry Pi Allied Stk #: 70689378
Keyboard/Mouse USB keyboard and mouse Allied Stock#: 70472529
D1 Blue LED (rectangular, ground to 4mm height) Radio Shack 276-0013
R1 270 Ω, ¼ W Allied Stk #: 70183331
R2 7mm diameter CdS LDR Any electronic parts store
R3 10 kΩ, ¼ W Allied Stk #: 70022898
R4 22 kΩ, ¼ W Allied Stk #: 70063067
R5 100 kΩ trimmer potentiometer Allied Stk #: 70154049
C1, C2 0.01 µF monolithic Allied Stk #: 70186297
C3, C5 0.1 µF monolithic Allied Stk #: 70186301
C4 10 µF / 25V tantalum Allied Stk #: 70195923
Perfboard (will eventually be PCB) 0.1” x 0.1” pefboard cut to 98 mm x 55 mm Allied Stk#: 70219540
GPIO Header Extra-tall stacking 40 pin header Adafruit ID: 19179
U1 MAX392 or similar low-impedance N.O. quad analog switch Mouser Electronics Part No. 700-MAX392CPE
U2 CD40106 Hex Schmitt Trigger Inverters Mouser Electronics Part No.595-CD40106BE
VCPA VCPA hacked from auto-darkening welding mask filter per text Online (Amazon, eBay, etc). Filter manufactured by “Mask” www.auto-mask.com (see Figure 13)
ADC ADS1015 Breakout Board - 12-Bit ADC -
4 Channel with Programmable Gain Amplifier
Allied Stock#: 70460623
DAC MCP4725 Breakout Board - 12-Bit DAC w/I2C Interface Allied Stock#: 70460904
Mechanical

LCP Enclosure 3D-printed enclosure 3D-print DOLPi3.stl
Enclosure Raspberry Pi Touchscreen Enclosure; For Use With:Raspberry Pi 7"Touch Screen with Pi B+ or Pi 2 Boards;
External Height: 131mm;
External Width: 213.2mm; External Depth: 51.5mm;
Element14 Catalog No. 55Y8475
Camera mounting screws Four M2.5 x 1” nylon machine screws and eight matching nylon nuts Hardware store
Tripod mounting block ¾” x ¾” x 4” aluminum machined as shown Machined from McMaster-Carr 9008K12

Images via David Prutchi

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