Page 1

EEWeb

PULSE

EEWeb.com

Issue 29 January 17, 2012

Tom Lee

Quanser, Inc.

Electrical Engineering Community


It’s all about

connections. EEWeb Electrical Engineering Community students

hobbyists

discussions

technical documents

industry experts engineers

white papers links

resources

Contact Us For Advertising Opportunities reference designs

1.800.574.2791application notes

advertising@eeweb.com power

www.eeweb.com/advertising lighting

community sensor

microcontroller wireless

The user-to-user forum is for everyone, from design engineers to hobbyists, to discuss technology, products, designs and more. Join the discussions that match your interest or offer your expertise to others. Join the discussion now at:

www.digikey.com/techxchange Digi-Key is an authorized distributor for all supplier partners. New products added daily. Š 2011 Digi-Key Corporation, 701 Brooks Ave. South, Thief River Falls, MN 56701, USA


TA B L E O F C O N T E N T S TABLE OF CONTENTS

4

Tom Lee QUANSER, INC. Interview with Tom Lee - Chief Education Officer

9

What’s New at Quanser? BY TOM LEE

An update on Quanser, Inc. and the direction they plan to take their products.

Featured Products The Route to PCB

11 12

BY PAUL CLARKE WITH EBM-PAPST Clarke describes his approach to PCB layout.

Understanding Incremental Encoder Signal

16

BY JIM MILLER WITH QUANTUM DEVICES How to get positional information from an incremental encoder.

RTZ - Return to Zero Comic

EEWeb | Electrical Engineering Community

19

Visit www.eeweb.com

3


TomLee INTERVIEW

Tom Lee - Chief Education Officer

Can you tell us a little bit about your background? My training is in engineering. I got my bachelor’s and master’s degrees in systems design engineering, which is an interdisciplinary program, from the University of Waterloo in Canada. The university thought that sometime in the future there would be a need for people to speak more than one engineering language, so it created this program. After several years in the program, I decided that I needed to get a bit more of a firm grounding on some of the more traditional engineering techniques. So I got my doctorate degree in mechanical engineering. That whole journey took about 14 years, and then in the late 1980s I got picked up by the company Maplesoft to try and figure out ways to present and transform what was essentially a pure mathematics and computer science software product into something that engineers would find appealing. At that time I was one of the few users of the Maple system in the engineering

EEWeb | Electrical Engineering Community

Visit www.eeweb.com

4

FEATURED INTERVIEW

Quanser, Inc.


INTERVIEW

I gained a lot of experience from those previous endeavors, and then this year the founders of Quanser approached me. I’ve known them for a long time, and they told me they were going on this exciting journey and wanted me to go with them. So I joined them about half a year ago. How would you define your role at Quanser? The core business that the company does is provide laboratory equipment and education solutions to universities. As Chief Education Officer, I am required to be able to deal with the formalism of education. We’ve gone past the point of just providing great tools and machines for lab exercises. We now have to look at how it all fits into the overall mandate of the university, as well as the emerging influences and trends of global industry. All of the major challenges that society faces that are typically worked out by engineers are now putting a huge demand on education systems. We do feel that we are part of the solution, and Quanser needed somebody with a fair amount of depth with regard to both technology and how people use technology for education. So what I do is help the company figure out strategies to

accelerate the transformation from a technology company to something very education-centric. So is the primary goal at Quanser to provide educational resources? Historically it wasn’t pure education. It was a series of mechatronics devices and robotic devices that were very high-precision and allowed researchers and educators to explore a lot of newer concepts in computer control of machines. In fact, most of our business for the first ten years was funded by

We’ve gone past the point of just providing great tools and machines for lab exercises. We now have to look at how it all fits into the overall mandate of the university, as well as the emerging influences and trends of global industry.

EEWeb | Electrical Engineering Community

the researchers who would purchase the machines, because they themselves couldn’t design machines of this kind of caliber. But the machines were so tuned to the kinds of experiments they were doing that the match was perfect. Along the way though, in the periphery, these devices started infiltrating the education side of the university, and professors who fell in love with the equipment would introduce it to their students. Concurrently, as that was happening, engineering as a community and society finally started embracing the whole notion of mechatronics and robotics. Probably the greatest examples of that were the FIRST Robotics Competitions for high school students, which now take place all over. It has become an immense initiative attracting all sorts of different schools, communities, and companies. So the combination of having the right technology and the trends in society aligning with it is what brought us to where we are today. Can you tell us more about the products you provide for students? If you consider junior and seniorlevel college students, you would typically see control systems courses. And in that context it is very common for students to be supplied with one of our machines moving around, allowing students to try controlling it, as well as observing its phenomena. Now, we’re looking much more into expanding beyond that, and there’s a lot of interest right now in getting some of these techniques from the higher-level courses down to the

Visit www.eeweb.com

5

FEATURED INTERVIEW

world, which is why I was picked up by the company. I was actually working in more of a marketing and sales context, and from that I was immersed in all sorts of different activities, both technical and more business oriented. All throughout, the theme of education was a very important part of what I was doing, both from a work point of view as well as a personal interest.


INTERVIEW

That’s the kind of creative thinking we’re trying to do right now, and these demands can be fully validated by lots of colleges that are really looking to enhance all parts of their education. Can you tell us more about the software you use? LabVIEW is a huge part of it, which is heavily influenced by our partnership with National Instruments. But there is a whole bag full of standard software that engineers use for control systems, modeling and dynamic analysis— all that kind of thing. So definitely LabVIEW, but prior to that, tools like Simulink were important. Even the product that I used to work on, Maple, is part of that family. We’re like any other modern or progressive engineering organization with our software tools. What kind of tool set is usually provided with the machines to control them? At the user level it will typically be something like LabVIEW, but we also offer our own software that provides several things that a regular computer cannot. A regular computer can’t really control these things because the machines have to be synchronized according to a real-time clock to allow the algorithms to work properly. With tools like LabVIEW, you don’t need some of the low-level stuff. But we also provide some high-level, easyto-use control environments for

students. Looking at some of the mechatronics control kits, do you provide models for students to help educate them? Yes. If you truly want to do engineering design right for the very challenging application areas that industry faces today, not only do you need the whole experimentation and testing—the machine side of things—you also need the modeling and simulation, which is the more theoretical side of things. One of the things we’ve always believed in is that it is not good enough just to provide hands-on experience. You need to provide that handson experience in context with the theories and principles the students are learning in the lectures. That whole thought is about modeling and simulation, and doing things more analytical in nature. What are some of your most exciting products for sale? One product that always caught my interest—partly because it’s reaching into an audience that is unconventional for a lot of companies like us—is called the Shake Table. It’s an earthquake simulation device. Basically, it looks like a giant bathroom scale on really heavy-duty motors, and it provides the necessary movement to simulate real earthquakes— not just from a bunch of random shaking; we can actually take the data recorded from a real historical earthquake and feed it into the machine for an accurate simulation of the earthquake. In the educational setting this is used

EEWeb | Electrical Engineering Community

for structural competitions, typically for civil engineering students. The students build structures, whether from toothpicks, LEGOs, or something similar, and they can actually test the quality of their design with a “real” earthquake. It’s a really interesting platform to do more than just hang a weight off of a bridge to see if it collapses. This adds another dimension to the testing process. On the other side, haptics is a technique to generate feeling on a controller of some sort. For example, if you have a steering wheel connected to a simulation device, we have techniques to actually project feeling onto the steering wheel. So if you’re in a simulation environment where you are in a collision, for instance if you’re hit by another car from behind, the feeling actually comes through the wheel. More in the area of things like biomedical engineering, there is actually an emerging set of techniques for training surgeons to do dangerous operations in a simulation environment using devices we provide, where surgeons do surgical maneuvers on virtual patients. In these cases, the feeling the surgeons get from the scalpel that is attached to one of our machines is very close to what they would feel in a real-life situation. Most of our applications tend not to be these romantic things like telemedicine or earthquake engineering; a lot of them are pretty fundamental devices. For example, we have what we call the rotary product line. It is sort of the Cadillac of control systems educational lab equipment. It has a modular

Visit www.eeweb.com

6

FEATURED INTERVIEW

freshman and sophomore levels. In those cases, they would be primarily for motivational purposes so students can see what they can expect from later lab experiences.


INTERVIEW

Do you provide suggested course material along with these products for professors to use when instructing their students? Yes, that’s one of the things that we’ve always prided ourselves in, and is

BeStar

in many ways what makes us so different from a lot of lab equipment companies. We put considerable effort into the curriculum side so every one of our products has related written material. By doing this, we try to significantly reduce the start-up effort by professors and TAs to introduce new equipment and concepts into a lab. This is one of the areas that I’m more directly involved in, and we’re really looking at new media techniques like video, audio and online resources for instruction, and I’m having a lot of fun with that. ■

®

FEATURED INTERVIEW

design where, based on a single servomotor, you can attach all sorts of different devices to serve various purposes. These tend not to be as big of applications as the others, but they do a great job of isolating key concepts while still providing some real down-to-earth application context.

Teamwork • Technology • Invention • Listen • Hear

ACOUSTICS & SENSORS PRODUCTS

INDUSTRIES

Speakers

Automotive

Buzzers

Durables

Piezo Elements

Medical

Back-up Alarms

Industrial

Horns

Mobile

Sirens/Bells

Fire / Safety

Beacons

Security

Microphones

Consumer

Sensors

Leisure

Preferred acoustic component supplier to OEMs worldwide

bestartech.com | sales@bestartech.com | 520.439.9204 EEWeb | Electrical Engineering Community Visit www.eeweb.com QS9000 • TS/ISO16949 • IS O 14001 • IS O 13485 • IS O 9001

7


Technology You Can Trust

Ultra Low Power Digital Optocouplers in Industrial Communication Interfaces 90% less power than standard optocouplers 40% lower power than alternative opto-isolators • Ultra low power • High temperature and supply voltage range • High noise immunity (35 kV/µs dynamic and static common mode rejection) • Certified for safe insulation (up to 1140 Vpeak continuous working voltage)

To request a free evaluation board go to: Avago Technologies new generation optocouplers, ACPL-x6xL series and www.avagotech.com/optocouplers ACNW261L, offer significant power efficiency improvements for industrial communication interfaces. With 35 years of experience in digital optocoupler design, Avago delivers quality you can count on. Optocouplers

ACPL-M61L/064L/W61L/K64L

Controller

Transceiver

Bus Line

Key Features


PROJECT

Quanser? By Tom Lee

Our company develops modern hands-on lab solutions for engineering education. The company was founded in 1989 with a goal of providing sophisticated mechatronic experiment rigs for research in a wide range

of application areas including robotics, aerospace, unmanned vehicles, haptics and telemedicine. The Quanser approach is unique in that it successfully integrates the benefits of true hands-on experiences with the flexibility of

Figure 1: A Quanser device for exploring haptics - control techniques that delivers force sensations as well as motion.

EEWeb | Electrical Engineering Community

software, and the necessary rigor of modeling and theory. The lab solution that we are most recognized for is the modern control systems laboratory, typically deployed in the third or fourth year of university. Digital control of complex engineering systems have become one of the most important engineering technologies of the 21st century and many universities have adopted the Quanser approach to modernize their control systems curriculum which has largely been unchanged for several decades in spite of the rapid advancements in industry. More recently, Quanser has been called to envision and develop solutions for a broader range of key educational contexts. For example, we began collaborating with leading universities to adapt Quanser solutions for the senior year capstone projects. Through the advanced equipment, students

Visit www.eeweb.com

9

FEATURED PROJECT

What’s New at


PROJECT Similarly, at the other end of the undergraduate time line, we have been active in developing new motivational lab experiences for the first year, general introduction to engineering courses. Our “Engineering Inspiration Lab” concept, which combines research-grade equipment with level-appropriate hands-on lab exercises, offers students a chance to experience truly innovative engineering in their first year of university. Sustainable engineering, earthquake engineering, biomedical engineering and high-performance automotive engineering are examples of some of the application contexts that can be introduced to the students. The concept of providing the best

equipment—which is historically reserved for graduate students—to keen freshmen, has gained strong interest from institutions, which see its potential as a powerful tool to improve recruitment, retention and success rates. Looking ahead, there is a wide range of such projects where we try to map our existing products to other modern educational needs. Examples include, distance and continuing engineering education (i.e., providing lab experience in distance education courses) as well as K-12 education (i.e., motivating and empowering students even before they arrive on campus).■

Figure 2: Quanser engineer, Peter Martin, developing a new lab exercise that combines a conventional experiment with video game style 3D animation.

EEWeb | Electrical Engineering Community

Visit www.eeweb.com

10

FEATURED PROJECT

are able to explore and experience true engineering workflows including design, analysis, project management and presentation. In some sense, the idea was to get the students to replicate our own design process for a complex device. One example was a ball balancing mechanism that required creative design of a system that used standard servo motor technology and a camera. Student groups would then figure out the additional mechanisms and the necessary control strategy to balance a ball on a flat plate. As it happens, Quanser actually offers such a device as part of its product line. So in essence, in a controlled environment, students replicated our own engineering workflow.


F E AT U R E D P R O D U C T S Microchip Technology Inc. today announced the HID-class MCP2210 USB to SPI protocol converter—the simplest, smallest-footprint and most cost-effective option for adding USB-Certified connectivity to SPIbased systems. Microchip also provides free downloads of supporting software drivers, DLLs and a PC configuration tool, in addition to an evaluation board, to make it fast and simple for designers without USB expertise to add USB connectivity. The converter comes in small, 20-pin SSOP and 5×5 mm QFN packages, for space-constrained applications. Additionally, the MCP2210 has nine flexible, general-purpose I/O that can be configured via a PC as standard digital I/O pins or in alternate configurations, providing additional system I/O that simplify designs and support a wide range of applications. For more information, please click here.

iNEMO® Body-Motion Sensor STMicroelectronics, a global semiconductor leader serving customers across the spectrum of electronics applications and the leading supplier of MEMS (Micro-Electro-Mechanical Systems) for consumer and portable applications 1, today unveiled a smart suit prototype with sewnin new multi-sensor ST iNEMO® motion co-processor that recognize complex movements of the wearer’s body and translate them to a digital model with outstanding precision and speed. The iBMR, iNEMO Body Motion Reconstruction technology could improve outcomes in clinical and sports medicine applications, as well as enhancing augmented reality where users could, for example, jog side by side with the world champion on their local running track. The current-generation prototype of ST’s body-motion reconstruction suit demonstrates the optimal performance of the miniaturized iNEMO multi-sensor nodes attached on each arm, forearm, thigh, calf, and two on the back; additional nodes can be mounted on hands, on shoes or on the head. For more information, please click here.

Gen4 TrueTouch® Controller Cypress Semiconductor Corp. introduced a new Gen4 TrueTouch® controller targeted at the rapidly growing tablet and ultrabook market. The new CY8CTMA1036 device has 65 sense-I/Os, enabling it to deliver flawless touchscreen performance for screens up to 12 inches. Like the smaller-screen Gen4 devices, it offers industry-best performance in all categories, including the world’s best signal-to-noise ratio (SNR) and unparalleled performance in the presence of all noise sources— the biggest challenge faced by touchscreen designs. Gen4 also has the lowest active power consumption, unparalleled tracking accuracy and the fastest refresh rates. It provides full support for major mobile operating systems including Win8 and Android. The new CY8CTMA1036 uses a 32-bit ARM® Cortex™ core, and offers 65 sensing I/O channels with support for up to 1036 nodes on the screen, 35 percent more than any other single-chip solution. Additional sensing channels are essential for greater accuracy, linearity, support for smaller sized fingers and the ability to resolve multiple fingers close together.For more information, please click here.

EEWeb | Electrical Engineering Community

Visit www.eeweb.com

11

FEATURED PRODUCTS

USB to SPI Converter


I currently use a software package called PADs at ebm-papst, which in my view is a great package if you can find someone else to afford and purchase it. However, no matter what package you use, you can still achieve the same results. So where do we start? Assuming that I have all the footprints I need and I’m happy with the

circuit drawings and components, I will print out the circuit schematics. It is important to have these at hand; you’re going to convert these line drawings into real copper. Next, I import or load up all the component footprints into my layout package. There are two possible approaches. You can either be an auto-route person or, like me, route the entire board by hand. For designs that do not have large numbers of buses

e rk er la ngine l C nE au esig

P sD c ni tro ec El

E TH

E UT CB RO P TO

W

hen it comes to turning your design or circuit into a real-life threedimensional object, there is one step that can make a big difference with it being successful. Laying out your PCB is just as important a skill as designing the circuit. In this article, I want to look at some of the key steps and the approach I take when taking the route to PCB.

and are primarily embedded micros, hand routing is just as quick as auto-routing. I say this because I would have to check track width rules like, “Is the net set to the correct width to carry the current?” I would also go back and check that signal lines are not next to power rails or noise sources. Therefore, in my head I can do this as I route and get the best layout I want, using my brain as the auto-router and designrule checker.

Figure 1: The Route to PCB

EEWeb | Electrical Engineering Community

Visit www.eeweb.com

12


TECHNICAL ARTICLE

Assuming I have a PCB outline, I will create a physical representation and start placing connectors—the ones that just have to go somewhere. I glue on the connectors so I can’t accidentally move them. It is then important to check PCB size and the location of the connectors to see if they fit in the enclosure. I then start routing the board in one of two ways. Most of my boards are two or four-layer. Regardless of the number of layers, I think about the board as a 3D object. The circuit layout can be broken down into two types: One type of layout deals more with analog circuits, having short routes between a resistor and an IC or between a few caps and regulators (Figure 2). The other type of layout is for, digital circuit with long runs of two or more routes running between multiple devices. One example would be routing a SPI bus (Figure 3). I try and start with the analog circuits and lay out the components and tracks as they appear in the

TECHNICAL ARTICLE

I start by grouping the components into areas around the outside of the board. For instance, let’s say I have a switch mode power supply—all these routes end up in a jumble over on one side. So do not overlap; just place them side-by-side in a grid to get an idea of the board area required. I do this for each block of the circuit, and this is why having the schematic in front of you is useful— you can see if the 100nF cap is for the power supply or needs to go next to an IC for decoupling. I move these blocks around until I can see where I want the flow or interfacing edges of each block to go until I’m ready to move on.

Figure 2: Analog

Figure 3: Digital

circuit diagram. If you don’t have a lot of overlapping nets in a 2D drawing then it should be easy to do the same on the PCB. I will keep it all to one side of the board if I can, which allows for another circuit to sit on the other side. I have

EEWeb | Electrical Engineering Community

used this technique often with RPM monitoring circuits for fans with the PWM drive circuit on the other side of the board. They both have to feed to and from the microcontroller and device—in this case a fan—so it is good if they run in parallel.

Visit www.eeweb.com

13


TECHNICAL ARTICLE

However, there are no hard rules, and when you have a digital embedded circuit you will have both layout types to deal with. This means that I will layout each block as it fits each layout profile above. Digital and analog lines from the micro will follow a more blue/red rule until they reach the analog-type circuits. This allows me to break out the signals from the micro and keep tight and compact analog circuits ring fenced from each other. There is, however, one very important part of the circuit I have not talked about yet—the power rails. Now it’s not hard to remember to connect power rails like your +5 or +3.3-volt lines, but people do forget about the ground or 0-volt rail. For each section of circuit or large device, I always check that I run a 0-volt trace out and connect it back. I try and use the “around the outside” rule. OK, not a great sounding rule but this means that I will have a track that runs around the entire outside of the board in a loop and then feeds into these blocks. It’s also good to highlight the whole track and see where it’s running. Can you bridge a gap (Figure 4)? The better your 0-volt connections,

the more likely your board will work well! Once complete, I then tackle the flood plan. Now I know not everyone worries about this but I do a copper flood on top and bottom connected to 0 volts. By maximizing the 0-volt tracks the flood will reach all parts of my board and I will have good connections throughout. Finally, I will run connection and clearance design rule checks that are built into PADs to flag silly errors before generating a final export to the mechanical engineer. He will, in my case, check that there aren’t any 0603 resistors sitting under an IC when it was meant to be on the back of the board. I only made that mistake once! I then can send off my files for the board to be made. It is a good idea to be certain that all the components will fit on the board. I once worked at a place where we had a PCB mill that could drill and cut the tracks from blank sheets of copper. This was a good way

to see if everything fit in the right place before spending money on prototype boards. There are many hard and fast rules you can add to your design approach, but these simple and basic principles allow me to design a board with minimal errors and reduce my chance of a re-spin. About the Author Paul Clarke is a digital electronics engineer with strong software skills in assembly and C for embedded systems. At ebm-papst, he develops embedded electronics for thermal management control solutions for the air movement industry. He is responsible for the entire development cycle, from working with customers on requirement specifications to circuit and PCB design, developing the software, release of drawings, and production support. ■

Figure 4: Ground Track

EEWeb | Electrical Engineering Community

Visit www.eeweb.com

14

TECHNICAL ARTICLE

For a digital layout, I will run the lines together as much as possible, but I do not try to only stay to one side of the board. I will, however, use a rule: blue = horizontal, red = vertical. The blue and red refer to the bottom and top sides of the board as it is displayed in the CAD package. By running these lines only horizontal on one side of the board and vertical on the other, it will minimize the number of board layers required.


Get the Datasheet and Order Samples http://www.intersil.com

Dual 800mA Low Quiescent Current 2.25MHz High Efficiency Synchronous Buck Regulator ISL78228

Features

The ISL78228 is a high efficiency, dual synchronous step-down DC/DC regulator that can deliver up to 800mA continuous output current per channel. The supply voltage range of 2.75V to 5.5V allows for the use of a 3.3V or 5V input. The current mode control architecture enables very low duty cycle operation at high frequency with fast transient response and excellent loop stability. The ISL78228 operates above the AM radio band as well as the 2.25MHz switching frequency, allowing for the use of small, low cost inductors and capacitors. Each channel is optimized for generating an output voltage as low as 0.6V.

• Internal Current Mode Compensation

The ISL78228 has a user configurable mode of operation-forced PWM mode and PFM/PWM mode. The forced PWM mode operation reduces noise and RF interference while the PFM mode operation provides high efficiency by reducing switching losses at light loads. In PFM mode of operation, both channels draw a total quiescent current of only 30µA, hence enabling high light load efficiency in order to maximize battery life. The ISL78228 offers a 1ms Power-Good (PG) to monitor both outputs at power-up. When shutdown, ISL78228 discharges the outputs capacitor. Other features include internal digital soft-start, enable for power sequence, overcurrent protection, and thermal shutdown. The ISL78228 is offered in a 3mmx3mm 10 Ld DFN package with 1mm maximum height. The complete converter occupies less than 1.8cm2 area.

• 100% Maximum Duty Cycle for Lowest Dropout • Selectable Forced PWM Mode and PFM Mode • External Synchronization up to 4MHz • Start-up with Pre-biased Output • Soft-Stop Output Discharge During Disabled • Internal Digital Soft-Start - 2ms • Power-Good (PG) Output with 1ms Delay • TS16949 Compliant • AEC - Q100 Tested • Pb-free (RoHS Compliant)

Applications • DC/DC POL Modules • µC/µP, FPGA and DSP Power • Rear Camera Systems • Navigation Systems • Infotainment Systems

The ISL78228 is both AEC - Q100 rated and fully TS16949 compliant. The ISL78228 is rated for the automotive temperature range (-40°C to +105°C).

100

EFFICIENCY (%)

90 80

2.5VOUT-PFM 1.8VOUT-PFM

70

2.5VOUT-PWM 60 1.8VOUT-PWM

50

VIN = 5V 40

0.0

0.1

0.2

0.3 0.4 0.5 OUTPUT LOAD (A)

0.6

0.7

0.8

FIGURE 1. EFFICIENCY CHARACTERISTICS CURVE

May 2, 2011 FN7849.0

Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2011 All Rights Reserved. All other trademarks mentioned are the property of their respective owners.


Understanding Incremental Encoder Signals Jim Miller

Application/design Engineer

Engineers using an incremental encoder for the first time often have a misunderstanding about what types of signals are provided by an encoder and how to interface an encoder to their application. They tend to know that an incremental encoder will be able to provide highly accurate positional information, but how to get this data from an incremental encoder is often a mystery. While there are many variations of incremental encoders, the most common provide three main channels of information: A, B and Z. Channels A and B provide identical square wave signals that correlate to the “line count” of the encoder. If the encoder has a resolution of 5,000 lines, there will be 5,000 pulses per revolution (PPR) on channel A and 5,000 PPR on channel B. Channels A and B offset from each other by 90 electrical degrees. This offset is known as quadrature and is used to determine direction of rotation. The term quadrature comes from the 90 electrical degree offset, as there are four 90-degree segments in a 360 electrical degree cycle.

360˚

1

A

2

3

4

B Figure 1

In one direction the leading edge of channel A will be before the leading edge of channel B. And in the opposite direction channel B will lead channel A. Channels A & B (Incremental Channels) Use only A (or only B) for a RPM or counting applications where the rotation is either unidirectional or where you don’t need to know direction.

A Figure 2

EEWeb | Electrical Engineering Community

Visit www.eeweb.com

16


TECHNICAL ARTICLE U V W

These signals can also be used to set up an up/down counter.

Figure 4

Index pulse, also known as Z, marker, or I

For a 5,000 line count encoder, this would mean locating a homing position to within 1/5,000 of a rotation or a precision of .072 Mechanical Degrees.

The Index pulse is a pulse that occurs once per rotation. It’s duration is nominally one A (or B) electrical cycle, but can be “gated.”

Commutation (UVW) signals are used to commutate or electrically time a brushless DC motor. I like to compare these signals to that of a distributor in a car. The commutation (sometimes called “Hall”) signals tell the motor windings when to fire (Figure 4).

The Index (Z) pulse can be used to verify correct pulse count.

A B

You would need to have encoder commutation signals if the motor you are mounting the encoder to has a pole count and there is no other device doing the commutation. It is important to note that commutation signals need to be aligned or “timed.”

Z Figure 3

Single-ended vs. Differential These terms refer not to the waveforms of signals, but instead to the way the signals are wired.

The Incremental Encoder Index pulse is commonly used for precision homing. As an example, a lead screw may bring a carriage back to a limit switch. It is the nature of limit switches to close at relatively imprecise points. This gives a coarse homing point. The machine can then rotate the lead screw until the Z pulse goes high, identifying a homing point with much higher precision.

Single-ended wiring uses one signal wire per channel and all signals are referenced to a common ground. “TTL” and Open Collector are types of single-ended wiring.

Noise Spike Occurs

Single Ended Wiring

Signal noise remains

RECEIVING DEVICE

ENCODER

Differential Wiring

Clean Signal

Noise Spike picked up on Signal

Signal as Seen by Device

RECEIVING DEVICE

ENCODER Signal noise canceled out

Figure 5

EEWeb | Electrical Engineering Community

Visit www.eeweb.com

17

TECHNICAL ARTICLE

Use A and B together to know direction. After two low pulses, the next high pulse indicates direction. This is due to the phasing offset between A and B of 90 electrical degrees, placing the signals in what is known as “quadrature.”


TECHNICAL ARTICLE can common-mode-error out a noise component that is picked up along the wiring.

Differential wiring is often employed in longer wire runs as any noise picked up on the wiring is common mode rejected.

Jim Miller is employed with Quantum Devices Inc, a leading manufacturer of optical rotary incremental Encoders. He plays a vital role in optical encoder design and development. â–

Figure 5 shows an example of how differential wiring

RS-422 is an example of differential wiring. About the Author

EEWeb EEWeb Electrical Engineering Community

Electrical Engineering Community

Join Today

Contact Us For Advertising Opportunities

1.800.574.2791

www.eeweb.com/register advertising@eeweb.com www.eeweb.com/advertising EEWeb | Electrical Engineering Community

Visit www.eeweb.com

18

TECHNICAL ARTICLE

Differential wiring uses two wires per channel that are referenced to each other. The signals on these wires are always 180 electrical degrees out of phase, or exact opposites. This wiring is useful for higher noise immunity, at the cost of having more electrical connections.


RETURN TO ZERO RETURN TO ZERO

EEWeb | Electrical Engineering Community

Visit www.eeweb.com

19


RETURN TO ZERO RETURN TO ZERO

EEWeb Electrical Engineering Community

Contact Us For Advertising Opportunities

1.800.574.2791

advertising@eeweb.com www.eeweb.com/advertising EEWeb | Electrical Engineering Community

Visit www.eeweb.com

20

EEWeb Pulse - Volume 29  

Interview with Tom Lee – Chief Education Officer; What’s New at Quanser?; The Route to PCB; Understanding Incremental Encoder Signal; RTZ –...