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:
| 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
