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Get your hands on a single OpticSpy unit and dive into the world of optical communications interfaces.


OpticSpy + Tomu Bundle

This bundle gives you an OpticSpy and Tomu, a tiny ARM microprocessor which fits in your USB port. With this combination of receiver and transmitter, you can easily set up your own optical interface between two computers.


OpticSpy 10-pack + Workshop

Have a team interested in learning more about optical covert channels and the details behind the OpticSpy? This OpticSpy 10-pack includes a two-hour online or local workshop (within the Portland, OR metro area) with creator Joe Grand. Joe will run through the design, functionality, tuning, and demonstrations of the OpticSpy and answer any questions regarding this or any of his other projects. The workshop will be scheduled for a mutually agreed upon date.


A tool to explore optical data transmissions and covert channels

As Featured In


"...with consumer Li-Fi looking promising, many of us are developing a growing interest in the technology, and OpticSpy is here just in time to help."

Geeky Gadgets

OpticSpy Lets You Explore Optical Data Transmissions

Blinkenlights are cool, but blinkenlights that send secret messages that are undetectable to the human eye are even cooler. OpticSpy is an open source hardware module for exploring and experimenting with optical data transmissions. It captures, amplifies, and converts an optical signal into a digital form that can be analyzed or decoded with a computer.

With OpticSpy, electronics hobbyists and hardware hackers can search for covert channels existing on modern devices, add optical data transfer functionality to a project, or capture and decode signals from remote controls and other consumer electronics that intentionally send information through light waves.

OpticSpy’s design is based on Maxim Integrated’s AN1117: Small Photodiode Receiver Handles Fiber-Optic Data Rates to 800kbps application note. We’ve added potentiometers for fine-tuning of a particular target signal, an on-board USB-to-serial interface for easy connection to a host computer, status indicator LEDs, and test points for observing each stage of signal processing. It has been successfully tested with both visible and near infrared light sources. Depending on the implementation of the LED transmission code on the target device, the LED can appear to be continuously on even though it’s blinking faster than the human eye can detect. That’s cool!

Why OpticSpy?

I’ve been playing around with optical covert channels for the past couple of years and wanted to create a simple device to look for and decode data hidden in optical signals. I thought providing OpticSpy as a fully assembled product would help others get more easily involved with optoelectronics.

Uses & Application Ideas

Features & Specifications

  • Easily converts light transmissions into digital signals
  • Gain and threshold adjustment via potentiometers for fine-tuning of a particular target
  • Supports both visible and near IR light emissions
  • On-board switch to select normal or inverted polarity data streams
  • USB interface for direct connection to host computer

OpticSpy is powered from the host computer’s USB port and uses an FTDI FT231X USB-to-Serial IC to provide the USB connectivity (drivers available directly from FTDI). When connected to a computer, OpticSpy will appear as a Virtual COM port and will have a COM port number automatically assigned to it. You can then use a terminal program (such as HyperTerminal, PuTTY, CoolTerm, minicom, or screen) to communicate with OpticSpy. Communication settings will vary depending on the type of optical transmission and encoding/modulation used. For our demonstrations (see the Demonstrations/Example Code section below), we are transmitting printable ASCII data via the target’s software- or hardware-based UART.

In the event that the device sending optical data is using a different encoding or modulation scheme not supported by a standard terminal program, you can preempt the FT231X interface by connecting a logic analyzer, Arduino, or any other tool capable of processing raw digital signals to the OpticSpy’s TP5 (Comparator Output) test point.

Bandwidth & Range

OpticSpy supports signals up to 800 kbps per the application note on which this design is based. I haven’t fully characterized the lower and upper speeds, but my experiments have ranged from 2400 to 115.2 kbps with no loss of data.

We’re using a Vishay Semiconductors BPW21R photodiode for the front end, which has an ideal spectral response from 420 to 675 nm. As opposed to typical photodiodes, which have a peak response for near IR, the BPW21R approximates the human eye making it more suitable for visible light. It is still quite sensitive to IR, allowing us to support a wider range of wavelengths.

OpticSpy is designed for higher bandwidth at the expense of sensitivity. The brighter the transmitting signal, the better the receive range will be. For my visible light transmission experiments, I’ve achieved ~1 inch with Tomu, which has a very bright LED, and directly on the surface with a TP-Link router, which has a not-so-bright LED shining through a lightpipe.

For near IR signals, like those from a TV remote control, distance is greater. With the Parallax Hackable Electronic Badge, which has a 1608-sized IR LED, I’ve gotten to ~3 inches. Depending on the OpticSpy gain settings, you can also use it to filter out the IR carrier/modulation (typically 30-56 kHz), killing two birds (capture and demodulation) with one stone. This is due to the high gain of the amplifiers reducing frequency response of the unit.

Demonstrations/Example Code

The following demonstrations transmit printable ASCII data with NRZ (Non-Return-to-Zero) encoding to emulate a standard UART interface.

All OpticSpy design documentation (including schematics, PCB/Gerber plots, and bill-of-materials) and code for the above examples are available on my Optical Covert Channels project page.


This project isn’t just based on theoretical concepts - optical covert channels and data transmissions via LEDs actually happen in the real world! I was inspired and motivated by many prior works (and a few recent ones), mostly involving methods of secretly exfiltrating data from compromised devices. Some of my favorites are listed here:

There are many ways to convert light into digital signals, most of which consist of a photodetector front-end and some amplification circuitry. OpticSpy is just one option, which I created specifically to make exploring different types of optical data transmissions easier. Here are a few other projects that could supplement your optical receiver toolkit or provide background information on optoelectronics:

  • Forrest Mims’ Engineer’s Mini Notebook: Optoelectronics Circuits originally published by Radio Shack in 1985 is a classic guide to all things optical.

  • Craig Heffner’s IRis project is a very sensitive, high gain amplifier designed to receive modulated IR signals from remote controls and proximity sensors on mobile phones.

  • The Dark Art Lab’s Building a laser microphone shows how to convert a hobbyist audio amplifier kit into a laser microphone that can receive sound modulated by a vibrating surface.

Manufacturing Plan

The units will be manufactured by e-Teknet, a PCB fabrication and assembly facility in mainland China. I’ve worked with them for nearly 20 years for many of my prototypes and high volume products. They were instrumental in building the first electronic badges ever created for DEFCON 14, 15, 16, 17 and 18, which contained complex board shapes and very tight deadlines. The production OpticSpy boards will have a black matte soldermask to reduce reflections from ambient light sources.

To have better control of the component supply chain, I will be ordering all components myself from trusted distributors and will perform incoming/quality inspection before sending them to e-Teknet.

I am in the process of creating a system-level test procedure, which will be used by the factory to individually test each unit durung production. This will ensure that all features are properly functioning before units are shipped to backers.

Risks & Challenges

The OpticSpy has gone through several development iterations and is ready for production. The PCB is a simple two-layer design with standard-sized SMT devices and a few through-hole components, so the risk of encountering technical problems during manufacturing is low.

All components are available in ample quantity from major parts distributors, so it is unlikely that we will have delays due to parts shortages.

As with any overseas process, our major risks are Customs issues and delays in shipping materials between China and the US.

Shipping & Fulfillment

The OpticSpy will be shipping from Crowd Supply’s Portland, Oregon warehouse. If you’d like to learn more about where, when and how things ship, please visit the Crowd Supply Guide.

Parts List

Digi-Key Part # Manufacturer Manufacturer Part # Reference Quantity Description
399-1170-1-ND Kemet C0805C104K5RACTU C1, C2, C3, C4, C5, C6, C7, C11, C14 9 Capacitor, 0.1 uF, 50 V, Ceramic, 10%, X7R, 0805
399-1158-1-ND Kemet C0805C103K5RACTU C8 1 Capacitor, 0.01 uF, 50 V, Ceramic, 10%, X7R, 0805
1276-1156-1-ND Samsung CL21C470JBANNNC C9, C10 2 Capacitor, 47 pF, 50 V, Ceramic, 5%, C0G, 0805
718-1956-1-ND Vishay Sprague 293D106X0016A2TE3 C12, C13 2 Capacitor, 10 uF, 16 V, Tantalum, 20%, Size A
311-1124-1-ND Yageo CC0805KRX7R9BB471 C15 1 Capacitor, 470 pF, 50 V, Ceramic, 10%, X7R, 0805
751-1013-ND Vishay Semiconductor BPW21R D1 1 Photodiode, Silicon PN, 420-675 nm, TO-5
754-1134-1-ND Kingbright APT2012SYCK D2, D3 2 LED, yellow clear, 150 mcd, 2.0 Vf, 590 nm, 0805
445-1568-1-ND TDK MPZ2012S221AT000 L1 1 Inductor, Ferrite Bead, 220 R @ 100 MHz, 3 A, 0805
H2960CT-ND Hirose Electric UX60-MB-5S8 P1 1 Connector Mini-USB, 5-pin, SMT w/ PCB mount
MMBT3904FSCT-ND ON Semiconductor MMBT3904 Q1 1 Transistor, NPN, 40 V, 200 mA, SOT23-3
P100KACT-ND Any Any R1 1 Resistor, 100k, 5%, 1/8 W, 0805
490-2667-1-ND Bourns PVG5A203C03R00 R2, R12 2 Resistor, variable trimmer, 20k, 1/8 W, SMD
P1.0KACT-ND Any Any R3, R6, R11 3 Resistor, 1k, 5%, 1/8 W, 0805
490-2674-1-ND Bourns PVG5A504C03R00 R4 1 Resistor, variable trimmer, 500k, 1/8 W, SMD
P4.7KACT-ND Any Any R5, R15, R16 3 Resistor, 4.7k, 5%, 1/8 W, 0805
P10KACT-ND Any Any R7, R8, R9 3 Resistor, 10k, 5%, 1/8 W, 0805
490-2663-1-ND Bourns PVG5A105C03R00 R10 1 Resistor, variable trimmer, 1.0M, 1/8 W, SMD
P27ACT-ND Any Any R13, R14 2 Resistor, 27 ohm, 5%, 1/8 W, 0805
401-2001-ND C&K Components JS202011CQN SW1 1 Switch, DPDT slide, 300 mA @ 6 VDC, PCB mount
MAX4124EUK+TCT-ND Maxim Integrated MAX4124EUK+T U1, U2 2 IC, Operational Amplifier, Rail-to-Rail, SOT23-5
MAX985EUK+TCT-ND Maxim Integrated MAX985EUK+T U3 1 IC, comparator, push-pull, rail-to-rail, SOT23-5
768-1129-1-ND FTDI FT231XS-R U4 1 IC, USB-to-UART bridge, SSOP20
576-1259-1-ND Microchip MIC5205-3.3YM5 U5 1 Linear regulator, LDO, 3.3 V, 150 mA, SOT23-5

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Grand Idea Studio

Grand Idea Studio is a product design, development, and licensing firm with a focus on consumer devices and open source modules for electronics hobbyists. It is run by computer engineer and hardware hacker Joe Grand.

Joe Grand


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