Passive Infrared Sensors

Homing in on Heat

One way to make sure that the lights get turned off when you leave a room is to use Passive Infrared (PIR) sensors. Jeff examines the science and technology behind PIR sensors. He then details how to craft effective program code and control electronics to use PIR sensors is a useful way.

By Jeff Bachiochi

“The last one to leave, please turn off the lights.” How many times did you hear this while growing up? It’s an iconic phrase sometimes used to suggest the end of life, but as I remember it, just an effort to save electricity. I would always use the logic that bulbs burn out during the initial surge current and not necessarily from remaining on, but that logic never worked on Mom. To this day I am obsessive about turning lights off (thanks Mom!). To that end I tried installing Passive Infra Red (PIR) sensors to handle this automatically. After being inundated with complaints (from my wife Beverly) about lights turning off “while I’m still in the room,” I gave up.

While PIR devices are sensitive to heat (infrared)—the human body’s radiation is strongest at a wavelength of 9.4 µm—they are based on the heat source moving past the sensor. Let’s look at a typical PIR sensor element to see how this works. The RE200B PIR sensor comes in a TO-5 package. Manufactured by Glolab, this device actually contains two sensors as seen in Figure 1.

FIGURE 1
The metal tab on the TO-5 can indicates the X-axis plane across both sensor elements. The window filter material is optimized for approximately 10 μm wavelength.

Each pyroelectric sensor is made of a crystalline material that generates a surface electric charge when exposed to heat. When the amount of radiation striking the crystal changes, so does amount of charge on the input to a sensitive FET device built into the sensor. The two elements are in series with the FET input connected to their junction. With this configuration and a wide (138-degree) field of view, whatever ambient light falls on both the sensors is canceled out. The sensor elements are sensitive to radiation over a wider range so a filter window is added to the TO-5 package to limit detectable radiation. As a standalone this device is not very useful. We need a way to interrupt the heat source from hitting both sensor elements at the same time.

Anyone familiar with opto encoders already understands how this works. Opto transmitter/receiver pairs are placed on opposite sides of a spoked wheel. Light passes between the spokes as it rotates between the pair. A second pair is placed such that when one light path is blocked by a spoke, the other light path is between spokes. As the spoked wheel rotates, the opto device’s output alternates between one coupled pair and the other. With some logic on the opto outputs, you can tell both direction and speed of the rotation. Creating the same kind of “picket fence” in front of the infrared (IR) sensor elements can cause the radiation to be alternately blocked and passed to each sensor. The trick will be to design the slat width and placement to give the desired effect.

Fresnel Lens

Figure 2
Lenses of large aperture and short
focal length are massive. The bulk
of the material can be eliminated as
long as the lens’ curve stays the same.
This can be accomplished by a series
of annular lens rings or the special grinding pattern on a single blank.

A lens could be used to artificially reduce the field of view, by collecting and focusing it into a smaller spot. Move an object in front of the lens left to right and the spot moves right to left, behind the lens. If the spot passes over the two sensor elements sequentially, voilà—each sensor will produce a push or pull at the center tapped output. And that is something we can detect. A single lens would create one sensitive area out in front of the device. This might be just what you are looking for. However, to be sensitive to a wider range we must have multiple lenses. Since glass is opaque to IR we can’t use a typical glass lens. It turns out that polyethylene type materials do pass IR light and can be formed in various Fresnel lens patterns.

The idea for the Fresnel lens goes back to the French mathematicians of the late 18th century. This was an attempt to make lenses thinner while retaining the optical quality of the original. Figure 2 shows how unnecessary thickness is removed from an original lens without changing the lens’ curvature. In the early 19th century this idea was adapted for use in lighthouses by Augustin-Jean Fresnel. The thin cross section of the Fresnel lens makes it ideal for PIR lenses. …

Read the full article in the June 335 issue of Circuit Cellar

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Gesture Recognition in a Boxing Glove

Sensors Packed in the Punch

Learn how these two Boston University graduate students built a gesture-detection wearable that acts as a building block for a larger fitness telemetry system. Using a Linux-based Gumstix Verdex, the wearable couples an inertial measurement unit with a pressure sensor embedded in a boxing glove.

By Blade Olson and Patrick Dillon

Diagnostic monitoring of physical activity is growing in demand for physical therapists, entertainment technologists, sports trainers and for postoperative monitoring with surgeons [1][2]. In response to the need for a low-cost, low-profile, versatile, extensible, wearable activity sensor, the Hit-Rec boxing sensor is a proof-of-concept device that demonstrates on-board gesture recognition and high-throughput data monitoring are possible on a wearable sensor that can withstand violent impacts. The Hit-Rec’s ability to gather raw sensor values and run calculations at a high frame rate make the Hit-Rec an ideal diagnostic device for physical therapists searching for slight perturbations across a user’s gestures in a single recording session or for looking at discrepancies between the ideal motions of a healthy individual and the user’s current motions. The following sections will describe the implementation of a prototype for the Hit-Rec using a boxing glove (See Lead Photo Above).

SYSTEM OVERVIEW

The Hit-Rec sensor incorporates a Gumstix Verdex Pro running Linux, a 9-DoF (degree of freedom) inertial measurement unit (IMU), a pressure sensor that is connected to the Gumstix via a 12-bit analog-to-digital converter (ADC) and LEDs for user feedback. The ADC and IMU both communicate over I2C. The LEDs communicate to the Gumstix through general purpose input/output (GPIO). Figure 1 shows a high-level explanation of hardware interfaces and Figure 2 provides an illustration of the system overview. All software was written in C and runs exclusively on the Gumstix Verdex Pro. A Linux kernel module was written to interact with the LEDs from the user-space program that performs data capture and analysis. IMU data was smoothed and corrected in real-time with an open-source attitude and heading reference system (AHRS) provided by Mahony [3][4]. A circular buffer queue was used to store and retrieve sensor data for recording and analysis. Punch classification compares accelerometer values at each data point and chooses the gesture with smallest discrepancy.

Figure 1
This high-level diagram details the data transfer connections made between the main hardware and software components of the Hit-Rec.

Figure 2
Overview of the software architecture for translating IMU and Pressure data to user feedback

Each of three LEDs on the Hit-Rec glove represents a different gesture type. After the “punchomatic” program is started, the user is prompted to record three gestures by way of three flashing LEDs. In the background, IMU data is continuously being recorded. The first, yellow LED flashes until an impact is registered, at which point the last 50 frames of IMU data are used as the “fingerprint“ for the gesture. This gesture fingerprint is stored for the rest of the session. Two additional gestures are recorded in an identical manner using the red and blue LEDs for the subsequent punches. After three gestures have been recorded, the user can punch in any form and the Hit-Rec will classify the new punch according to the three recently recorded punch gestures. Feedback on the most closely related punch is presented by lighting up the corresponding LED of the originally recorded gesture when a new punch occurs.

SENSORS

We used the Adafruit LSM9DS0 with breakout board as an IMU sensor and a force-sensitive resistor (FSR) from Adafruit as a pressure sensor. Both sensors communicate over I2C, which the pressure sensor achieves through an ADC. …

Read the full article in the June 335 issue of Circuit Cellar

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Device Silences TV Commercials

Arduino-Controlled Solution

Ever wish you could block out those annoying TV ads? Tommy describes in detail how he built a device for easily muting the audio of commercials. His project relies on three modules: a UHF radio receiver, an IR module and an Arduino Trinket board.

By Tommy Tyler

Does your blood start to boil as soon as one of those people on TV tries to sell you precious metals, a reverse mortgage, a miraculous kitchen gadget or an incredible weight reduction plan? Do you want to climb the wall the next time someone says “But wait! Order now and get a second one free . . .“? Believe it or not, there was a time long ago when TV commercials were actually entertaining. That was before commercial breaks evolved from 30 second or one-minute interruptions into strings of a half-dozen or more advertisements linked end-to-end for three to five minutes—sometimes with the exact same commercial shown twice in the same group! What is perhaps most annoying is the relentless repetition.

Historically, all the feeble attempts at TV commercial elimination have been applied to recordings on VCRs or DVRs. Anyone who watches programming that’s best enjoyed when viewed in real-time—news, weather and sports—has probably wished at one time or another for a device that can enable them to avoid commercials. They long for a device that could be inserted between their TV and the program source—whether it be cable, satellite or an OTA antenna—to instantly recognize a commercial and blank the screen, change channels or somehow make it go away. The technology for doing that does exist, but you’ll probably never find it applied to consumer products. Since funding of the entire television broadcast industry is derived from paid advertisements, any company that interferes with that would face enormous opposition and legal problems.

After many years of searching the Internet I’ve concluded it is wishful thinking to expect anyone to market a product that automatically eliminates commercials in real-time. I decided to work instead on the next-best approach I could think of: A device that makes it quick and easy to minimize the nuisance of commercials with the least amount of manual effort possible. This article describes a “Kommercial Killer (KK)” that is controlled by a small radio transmitter you carry with you so it’s easily and instantly accessible. No scrambling to find that clumsy infrared remote control and aim it at the TV when a commercial starts. Just press the personal button that’s always with you, even while remaining warm and cozy curled up under a blanket.

Kommercial Killer

The KK operates from anywhere in the home, even from another room completely out of sight of the TV and can be triggered at the slightest sound of an advertisement, political message, solicitation or perhaps even a telephone call. It works with any brand and model TV without modifications or complicated wiring connections by using the TV’s infrared remote control system. If you get a new TV, its remote control can easily teach KK a different MUTE command. Don’t worry about leaving the room with the TV muted. KK automatically restores audio after a certain amount of time. The default time is three minutes, the length of a typical commercial break, but you can easily configure this to any amount of time you prefer. And when you want to restore audio immediately—for example if you have muted non-commercial program material by mistake or if a commercial runs shorter than expected—just press your transmitter button again.

Figure 1
Schematic of the Kommercial Killer

KK is built mainly from three commercially available modules that do all the heavy lifting (Figure 1). The first module is a miniature UHF radio receiver. The second is an infrared module that can learn and mimic the TV mute signal. The third module is an Arduino Trinket board that provides commercial break timing and overall control. This article explains how to load a small program into that module without needing any special equipment or training, and even if you have absolutely no previous experience with Arduino devices.

The three modules are small and inexpensive ($7 to $10 each) and with just eight additional components KK can be built on an open perf board, strip board or enclosed in a 6-inch3 box. It is powered from the same USB Micro cable you use to load or modify the Arduino program, or from any other available USB port or 5 V charger.

UHF Receiver Module

The best UHF radio transmitters and receivers are all manufactured in China, and there are no major distributors in the U.S. So, order this item early and be prepared to wait about 20 days for delivery. After sampling many different remote controls to evaluate performance, quality, cost and shipment, I selected a product manufactured by the Shenzhen YK Remote Control Electronics Company, whose products are sold and shipped through AliExpress. Shenzhen remote controls use two types of receivers. . …

Read the full article in the May 334 issue of Circuit Cellar

After you’ve read the full article, don’t forget to go the the Article Materials Page for useful links and information.
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HDMI TFT Modules Simplify Connectivity

HDMI TFT module product line that greatly simplifies the process of connecting to the display. Rather than juggling an FPC ribbon cable with a middle-man controller board, you can connect an HDMI cable from your desired board or computer right into the TFT module. This makes it easy to interface with your display from the development and prototyping stages, all the way into final application production.

The ease-of-use of these new products follows through into touch panel integration as well. For both the resistive and capacitive (PCAP) touch panel options, USB-HID driver recognition is installed. Each of the touch panel modules are also each pre-calibrated in-house to the display they’re mounted on. This means that a simple USB to micro-USB cable just needs to be connected from your board with touch interaction output (such as Raspberry Pi) to the module and your touch interactivity is ready to go immediately.

Smart Power Switches Meet Automotive Needs

Infineon Technologies offers power IC manufacturing technology: SMART7. Infineon designed it specifically for automotive applications such as Body Control Modules or Power Distribution Centers. SMART7 power ICs drive, diagnose and protect loads in applications like heating, power distribution, air-conditioning, exterior and interior lighting, seat and mirror adjustment. They also provide a cost-effective and robust replacement of electromechanical relays and fuses. SMART7 is based on thin-wafer technology that reduces power losses and chip sizes. Based on SMART7, Infineon has introduced the two high-side power switch families PROFET+2 and High Current PROFET. The SPOC+2 multichannel SPI high-side power controllers will follow within a year.

Infineon High Res PROFET TSDSO-14

The PROFET+2 family was developed for automotive 12 V lighting load applications and capacitive loads. These comprise e. g. halogen bulbs in external lighting control, interior lighting and dimming, as well as LED lighting. PROFET+2 devices provide state-of-the-art diagnostics and protection features. They maintain pin-out compatibility with their predecessor family PROFET+ for zero-cost migration. There is no ECU layout change needed, if single-channel devices are replaced by dual-channel variants and vice versa. Compared to their predecessor family, the PROFET+2 devices are up to 40 percent smaller in package size and improve energy efficiency with 50 percent lower current consumption. Their mass production is planned to start as of Q4 2017 and later. All high-side switches will be qualified in accordance with AEC Q100.

Infineon Technologies | www.infineon.com

Client Profile: Newhaven Display International, Inc.

About Newhaven Display
Since 2001, Newhaven Display has been providing the worldwide marketplace with cost-effective, high-quality displays, including OLEDs, LCDs, and VFDs. In addition to its vast standard part offerings, Newhaven Display develops custom display designs for all industries. It prides itself on first-rate customer support, design services, and development assistance.
At its Elgin, IL headquarters, Newhaven Display performs product quality inspections, stock, design, develop, manufacture, and assemble our display products. All of its partnered production centers are state-of-the-art facilities with extensive experience in display development. Newhaven Display works closely with its production centers to ensure its products meet all requirements of proper design and quality standards.

NewhavenDisplay

Why Should CC Readers Be Interested?
Newhaven Display offers a variety of high-quality TFT displays. Ranging from 1.8” to 7.0”, these TFTs come ready with the option of capacitive or resistive touch and are available as standard, Premium (MVA), or Sunlight Readable displays. When wider viewing areas are needed, the Premium TFTs have up to 75° view from all sides, whereas the Sunlight Readable TFTs are the ideal option for outdoor applications.
To help with developing with these TFTs, Newhaven Display also has plug-and-play BeagleBone and Arduino development boards that make prototyping a breeze. Developed and designed by Newhaven Display’s engineers in Elgin, IL, these boards are perfect for any level of engineer looking to get started with TFT development. For high-quality, brilliant TFT displays and development assistance, turn to Newhaven Display.

Elgin, IL, USA
www.newhavendisplay.com

LUXEON UV U1 Offers 2× Performance Smallest UV Emitter

Lumileds recently announced the LUXEON UV U1 LED for use in a variety of UV applications, including UV curing, counterfeit detection, analytical instrumentation, inspections and other UVA and Violet (380–420 nm). Featuring the same micro package size as LUXEON Z UV, the new version enables a higher power density.

The LUXEON UV U1 LED is nominally tested at 500 mA, but it can be driven at up to 1 A to achieve higher irradiances. For the application of UV curing at 395 nm, LUXEON UV U1 achieves 700 mW at 500 mA and greater than 1300 mW at 1 A under 25°C. Compared to the 3.5 × 3.5 mm2 package size of most UV LEDs, LUXEON UV U1’s unique micro package size delivers superior packing density as well as greater than 5× higher power density. The LUXEON UV U1’s footprint is a drop-in replacement for the LUXEON Z UV, while providing twice the typical radiometric power as its predecessor at 380–390 nm.

Source: Lumileds

Future-Proof, Next-Gen Wireless LED Lighting Solution

GreenPeak Technologies recently launched a wireless low-cost ambient lighting application based on the new GreenPeak GP651 communication chip that can support various ZigBee and IEEE 802.15.4 communication protocols. The solution can combine LED lights with smart ambient applications to provide you with the freedom to create a variety of lighting scenes. The solution supports one- , two-, and four-channel LED bulbs. You can control settings and time schedules via a Smart Home system, a smart phone, or a basic wireless switch.GreenPeak Infographic LED GP651

The GP651 is a low-cost, small footprint (QFN32), single-chip solution. Additional cost savings can be achieved because of its 125°C (257°F) spec, reducing the size of a heatsink, enabling a compact and creative product design, and reducing the complexity of manufacturing resulting in a low total BOM.

Source: GreenPeak Technologies

60-V LED Driver with Internal 4-A Switch & PWM Generator

Linear Technology’s LT3952 is a current mode step-up DC/DC converter with an internal 60-V, 4-A DMOS power switch. It is specifically designed to drive high power LEDs in multiple configurations. It combines input and output current regulation loops with output voltage regulation to operate as a flexible current/voltage source.  The LT3952’s 3-to-42-V input voltage range makes it ideal for a wide variety of applications, including automotive, industrial, and architectural lighting.Linear 3952

The LT3952 can drive up to 16 350-mA white LEDs from a nominal 12-V input, delivering in excess of 15 W. It incorporates a high side current sense, enabling its use in boost mode, buck mode, buck-boost mode or SEPIC topologies. Internal spread spectrum frequency modulation minimizes EMI concerns. The LT3952 delivers efficiencies of over 94% in the boost topology, eliminating the need for external heat sinking, and internal LED short-circuit protection enables added reliability required in most applications. A frequency adjust pin permits the user to program the switching frequency between 200 kHz and 3 MHz, optimizing efficiency while minimizing external component size and cost. The LT3952 delivers over 90% efficiency while switching at 2 MHz in a tiny solution footprint. The LT3952 provides a very compact high power LED driver solution in a thermally enhanced TSSOP-28E package.

The LT3952 has a gate driver for a PMOS LED disconnect switch, delivering dimming ratios of up to 4,000:1 using an external PWM signal. For less demanding dimming requirements, the CTRL pin can be used to offer a 10:1 analog dimming range and an internal PWM generator can be used for 5:1 dimming. The LT3952’s fixed frequency, current-mode architecture offers stable operation over a wide range of supply and output voltages. Output short-circuit protection and open LED protection enhance system reliability. Other features include frequency synchronization, spread spectrum frequency modulation, programmable VIN undervoltage and overvoltage protection, and an input current limit and monitor.

The LT3952EFE is available in a thermally enhanced 28-lead TSSOP package. Three temperature grades are available, with operation from –40°C to 125°C (junction) for the extended, and industrial grades, and a high temperature grade of –40°C to 150°C. Pricing starts at $3.95 each in 1,000-piece quantities and all versions are available from stock. For more information, visit www.linear.com/product/LT3952

Source: Linear Technology

New Power Factor-Corrected AC-DC Drivers for LED Lighting Apps

ON Semiconductor has announced two new series of power factor corrected (PFC) offline AC-DC drivers for high performance LED lighting applications. Extending the NCL3008x family of products, the NCL30085, NCL30086, and NCL30088 address single-stage design implementations up to 60 W that require high power factor. The NCL30030 broadens the existing solutions which support higher power (up to 150 W) two-stage topologies that require low optical ripple and wide LED forward voltage variation.

 

Source: ON Semiconductor

Source: ON Semiconductor

The NCL30085, NCL30086, and NCL30088 use a PFC current control algorithm that makes them suitable for flyback buck-boost and SEPIC topologies. By operating in quasi-resonant mode, they can deliver optimum efficiency across wide line and load levels. The innovative control methodology enables strict current regulation to be achieved (within 2% typically) solely from the primary side.

 

The non-dimmable NCL30088 is complemented by the “smart-dimmable” NCL30086, supporting analog and pulse-width modulation (PWM) dimming with a single input that controls the average LED current. Completing the series is the NCL30085, which supports three levels of log step dimming: 70%, 25%, and 5%. As a result, it permits light output reduction by toggling the AC switch on/off to signal the controller to lower the LED current point. All three devices feature user-configurable current thermal fold-back mechanisms that help prevent overheating and enable manufacturers to support longer lifetime warranties.

 

The NCL30085 and NCL30088 are available in SOIC-8 packages. The NCL30086 is offered in an SOIC-10 package with pricing of the series starting at $0.35 per unit in 10,000-piece quantities.

 

The NCL30030 is a two-stage PFC controller plus quasi-resonant flyback controller optimized for medium and high power LED lighting applications up to 150 W. This device is best suited for commercial lighting such as lowbay, highbay, and streetlighting. The NCL30030 makes use of a proprietary multiplier architecture to achieve low harmonic distortion and near-unity power factor while operating in critical conduction mode (CrM).

The NCL30030 is in an SOIC−16 package with one pin removed for high-voltage spacing. Pricing starts at $0.65 per unit in 10,000-piece quantities.

 

Source: ON Semiconductor

LED Light Engines Deliver Up to 4,000 Lumens

Innovations in Optics has announced  high-power white LED light engines for OEM fiberoptic illumination. LumiBright Light Engines couple directly to liquid light guides and fiber bundles with no additional optics. They deliver up to 4,000 lumens into the light guide.

The 2400-W (Source:

The 2400-W (Source: Innovations in Optics)

Offering substantial cost and operational advantages, white LEDs are becoming popular light guide illumination sources for many technical applications that were historically dominated by tungsten halogen and HID lamps. LumiBright light engines feature patented technologies that encompass non-imaging optics with chip-on-board (COB) LED arrays on metal core circuit boards to provide both optimum luminous efficacy and ideal thermal management. Unlike the so called “big chip” LEDs used in many light guide illuminators, LumiBright light engines feature large source size and emit into a numerical aperture that matches the acceptance cone angle and diameter of light guide systems. The unique design results in many more lumens emitted from light guides relative to the big chip Lambertian emitters.

The LumiBright 2400B-400-W has a 0.66 numerical aperture (NA) and illuminates fiber bundles and light guides sized from 6.0 to 8.0 mm in diameter. Well suited for applications in machine vision and remote source illumination, the light engine generates up to 4,000 lumens. The 2400B-500-W is ideally suited for endoscope and microscope illuminator applications with a 0.60 NA for light guides that are 3.0 to 5.0 mm in diameter. The 2400B-500-W produces up to 1,500 lumens. Available light engine system accessories include thermal management devices, wire harnesses, and driver/controllers.

Source: Innovations in Optics

Data Communication Between “Smart” Pendants

As head of the Computer Science and Software  Engineering department at Penn State Erie, The Behrend College, Chris Coulston is busy.

But not too busy to surf the ‘Net for design inspiration.

And one of his latest projects may earn him the title of “social jewelry designer,” along with college professor and department chair.

In the June issue of Circuit Cellar, Coulston writes about his design and construction of an RGB LED pendant that “cycles through a color sequence, detects when another pendant is brought into its proximity, and communicates color sequence information to the other pendant through its LED.” The heart of the design is a Seoul Semiconductor SFT722 RGB LED.

Coulston was online a few years ago when he ran across the first half of his project inspiration—a Mitsubishi Electric Research Laboratories technical report titled “Very Low-Cost Sensing and Communication Using Bi-directional LEDs.” The report, Coulston says, “describes how an ordinary LED with no additional circuitry can act as a full-duplex communication channel.”

Pendant’s two boards

His remaining inspiration came from an article he recalled appearing in Circuit Cellar a decade ago.

The Mitsubishi labs technical report “got me thinking about Jeff Bachiochi’s article ‘Designing with RGB LEDs’ (Circuit Cellar 159, 2003), in which the challenges associated with designing a piece of LED jewelry are described,” Coulston says. “The fusion of these two ideas was the inspiration for my social jewelry design.”

Coulston’s design includes a pair of circuit boards, the upper containing the LED and analog circuitry and the lower containing the microcontroller.

“The prototype pendant is mainly controlled through a USB-to-USART bridge,” Couston says. “Its power is supplied by the same connection.”

He invites anyone who is  “curious how an LED can be used as a transceiver and how it’s used to build a piece of social jewelry” to read his article. You’ll find it in next month’s issue of Circuit Cellar.

Q&A: Raspberry Pi Innovation

Orlando, FL-based web app developer and blogger Shea Silverman recently received Kickstarter funding for the latest version of PiPlay, his Raspberry Pi-based OS. Shea and I discussed his ongoing projects, his Raspberry Pi book, and what’s next for PiPlay.—Nan Price, Associate Editor

 

silverman

Shea Silverman

NAN: What is your current occupation?

SHEA: Web applications developer with the Center for Distributed Learning at the University of Central Florida (UCF).

NAN: Why and when did you decide to start your blog?

SHEA: I’ve been blogging on and off for years, but I could never keep to a schedule or really commit myself to writing. After I started working on side projects, I realized I needed a place to store tips and tricks I had figured out. I installed WordPress, posted some PhoneGap tips, and within a day got a comment from someone who had the same issue, and my tips helped them out. I have been blogging ever since. I make sure to post every Friday night.

NAN: Tell us about PiPlay, the Raspberry Pi OS. Why did you start the OS? What new developments, if any, are you working on?

piplay-case

Shea’s PiPlay Raspberry Pi OS recently reached 400% funding on Kickstarter.

SHEA: PiPlay is a gaming and emulation distribution for the Raspberry Pi single-board computer. It is built on top of the Raspbian OS, and tries to make it as easy as possible to play games on your Raspberry Pi. My blog got really popular after I started posting binaries and tutorials on how to compile different emulators to the Raspberry Pi, but I kept getting asked the same questions and saw users struggling with the same consistent issues.

I decided I would release a disk image with everything preconfigured and ready to be loaded onto an SD card. I’ve been adding new emulators, games, and tools to it ever since.

I just recently completed a Kickstarter that is funding the next release, which includes a much nicer front end, a web GUI, and a better controller configuration system.

NAN: You wrote Instant Raspberry Pi Gaming. Do you consider this book introductory or is it written for the more experienced engineer?

SHEA: Instant Raspberry Pi Gaming is written like a cookbook with recipes for doing various tasks. Some of them are very simple, and they build up to some more advanced recipes. One of the easier tasks is creating your user account on the Pi Store, while the more advanced recipes have you working with Python and using an API to interact with Minecraft.

Readers will learn how to setup a Raspberry Pi, install and use various emulators and games, a bit about the Minecraft API, and common troubleshooting tips.

pitroller

The Pitroller is a joystick and buttons hooked up to the GPIO pins of a Raspberry Pi, which can act as a controller or keyboard for various emulators.

NAN: You are a member of FamiLAB, an Orlando, FL-based community lab/hackerspace. What types of projects have you worked on at the lab?

miniarcade

Disney director Rich Moore poses with Shea’s miniature arcade machine. The machine was based on Fix It Felix Jr. from Disney’s Wreck It Ralph.

SHEA: I spend a lot of time at the lab using the laser cutter. Creating a 2-D vector in Inkscape, and then watching it be cut out on a piece of wood or acrylic is really inspiring. My favorite project was making a little arcade machine featuring Fix It Felix Jr. from Wreck It Ralph. A marketing person from Disney was able to get it into the hands of the director Rich Moore. He sent me a bunch of pictures of himself holding my little arcade machine next to the full size version.

NAN: Give us a little background information. How did you become interested in technology?

SHEA: My mom always likes to remind me that I’ve been using computers since I was 2. My parents were very interested in technology and encouraged my curiosity when it came to computers. I always liked to take something apart and see how it worked, and then try to put it back together. As the years went on, I’ve devoted more and more time to making technology a major part of my life.

NAN: Tell us about the first embedded system you designed.

SHEA: I have a lot of designs, but I don’t think I’ve ever finished one. I’ll be halfway into a project, learn about something new, then cannibalize what I was working on and repurpose it for my new idea. One of the first embedded projects I worked on was a paintball board made out of a PICAXE microcontroller. I never got it small enough to fit inside the paintball marker, but it was really cool to see everything in action. The best part was when I finally had that “ah-ha!” moment, and everything I was learning finally clicked.

NAN: What was the last electronics-design related product you purchased and what type of project did you use it with?

SHEA: At UCF, one of our teams utilizes a ticket system for dealing with requests. Our department does a hack day each semester, so my coworker and I decided to rig up a system that changes the color of the lights in the office depending on the urgency of requests in the box. We coded up an API and had a Raspberry Pi ping the API every few minutes for updates. We then hooked up two Arduinos to the Raspberry Pi and color-changing LED strips to the Arduinos. We set it up and it’s been working for the past year and a half, alerting the team with different colors when there is work to do.

NAN: Are you currently working on or planning any projects?

SHEA: My Kickstarter for PiPlay just finished at 400% funding. So right now I’m busy working on fulfilling the rewards, and writing the latest version of PiPlay.

NAN: What do you consider to be the “next big thing” in the industry?

SHEA: Wearable computing. Google Glass, the Pebble smart watch, Galaxy Gear—I think these are all great indicators of where our technology is heading. We currently have very powerful computers in our pockets with all kinds of sensors and gadgets built in, but very limited ways to physically interact with them (via the screen, or a keypad). If we can make the input devices modular, be it your watch, a heads-up display, or something else, I think that is going to spark a new revolution in user experiences.

Battery Charger Design (EE Tip #130)

It’s easy to design a good, inexpensive charger. There is no justification for selling cheap, inadequate contraptions. Many companies (e.g., Linear Technology, Maxim, Semtech, and Texas Instruments) supply inexpensive battery management ICs. With a few external parts, you can build a perfect charger for just about any battery.

Texas Instruments’s UC2906 is an older (Unitrode) IC designed to build an excellent sealed lead-acid battery charger with a sophisticated charging profile. Figure 1 shows the recommended charger circuit.

Figure 1: This lead-acid battery charger uses Texas Instruments’s UC2906 IC.

Figure 1: This lead-acid battery charger uses Texas Instruments’s UC2906 IC.

In addition to the IC, only a handful of resistors and a PNP power transistor Q1 are needed to build it. Q1 must be rated for the maximum charging current and fitted with a heatsink.

An LED with its current-limiting resistor R can be connected to pin 7, which is an open-collector NPN transistor, to indicate the presence of power. Similarly, an LED with a series resistor could be connected to pin 9, which is also an open-collector NPN transistor to indicate overcharge (it is not used in Figure 1). The UC2906 datasheet and the Application Note provide tables and equations for selection of resistors Rs, Rt, RA, RB, RC, and RD and suggestions for adding various features.

Editor’s Note: This is an excerpt from an article written by George Novacek, “Battery Basics (Part 3): Battery Management ICs,” Circuit Cellar 280, 2013.

The Future of Monolithically Integrated LED Arrays

LEDs are ubiquitous in our electronic lives. They are widely used in notification lighting, flash photography, and light bulbs, to name a few. For displays, LEDs have been commercialized as backlights in televisions and projectors. However, their use in image formation has been limited.

A prototype emissive LED display chip is shown. The chip includes an emissive compass pattern ready to embed into new applications.

A prototype emissive LED display chip is shown. The chip includes an emissive compass pattern ready to embed into new applications.

The developing arena of monolithically integrated LED arrays, which involves fabricating millions of LEDs with corresponding transistors on a single chip, provides many new applications not possible with current technologies, as the LEDs can simultaneously act as the backlight and the image source.

The common method of creating images is to first generate light (using LEDs) and then filter that light using a spatial light modulator. The filter could be an LCD, liquid crystal on silicon (LCoS), or a digital micromirror device (DMD) such as a Digital Light Processing (DLP) projector. The filtering processes cause significant loss of light in these systems, despite the brightness available from LEDs. For example, a typical LCD uses only 1% to 5% of the light generated.

Two pieces are essential to a display: a light source and a light controller. In most display technologies, the light source and light control functionalities are served by two separate components (e.g., an LED backlight and an LCD). However, in emissive displays, both functionalities are combined into a single component, enabling light to be directly controlled without the inherent inefficiencies and losses associated with filtering. Because each light-emitting pixel is individually controlled, light can be generated and emitted exactly where and when needed.

Emissive displays have been developed in all sizes. Very-large-format “Times Square” and stadium displays are powered by large arrays of individual conventional LEDs, while new organic LED (OLED) materials are found in televisions, mobile phones, and other micro-size applications. However, there is still a void. Emissive “Times Square” displays cannot be scaled to small sizes and emissive OLEDs do not have the brightness available for outdoor environments and newer envisioned applications. An emissive display with high brightness but in a micro format is required for applications such as embedded cell phone projectors or displays on see-through glasses.

We know that optimization by the entire LED industry has made LEDs the brightest controllable light source available. We also know that a display requires a light source and a method of controlling the light. So, why not make an array of LEDs and control individual LEDs with a matching array of transistors?

The marrying of LED materials (light source) to transistors (light control) has long been researched. There are three approaches to this problem: fabricate the LEDs and transistors separately, then bond them together; fabricate transistors first, then integrate LEDs on top; and fabricate LEDs first, then integrate transistors on top. The first method is not monolithic. Two fabricated chips are electrically and mechanically bonded, limiting integration density and thus final display resolutions. The second method, starting with transistors and then growing LEDs, offers some advantages in monolithic (single-wafer) processing, but growth of high-quality, high-efficiency LEDs on transistors has proven difficult.

My start-up company, Lumiode (www.lumiode.com), is developing the third method, starting with optimized LEDs and then fabricating silicon transistors on top. This leverages existing LED materials for efficient light output. It also requires careful fabrication of the integrated transistor layer as to not damage the underlying LED structures. The core technology uses a laser method to provide extremely local high temperatures to the silicon while preventing thermal damage to the LED. This overcomes typical process incompatibilities, which have previously held back development of monolithically integrated LED arrays. In the end, there is an array of LEDs (light source) and corresponding transistors to control each individual LED (light control), which can reach the brightness and density requirements of future microdisplays.

Regardless of the specific integration method employed, a monolithically integrated LED and transistor structure creates a new range of applications requiring higher efficiency and brightness. The brightness available from integrated LED arrays can enable projection on truly see-through glass, even in outdoor daylight environments. The efficiency of an emissive display enables extended battery lifetimes and device portability. Perhaps we can soon achieve the types of displays dreamed up in movies.