EEWeb Pulse 124: May, 2014

Dell Compellent’s

Storage Array Speeds and Scalability Interview with Alan Atkinson VP & GM of Dell Storage

Optimal Membrane Switch Design Reducing BOM in LED Designs

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CONTENTS

PULSE

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Featured Products

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This week’s latest products from EEWeb.

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10 SHIFT REGISTERS16 to Reduce Size and BOM in LED Designs 26 26 An Intro to PID Controllers

Using

The first part of the series aims to demystify the mathematical tunings involved in using PID controllers.

Dell Compellent SC8000

Offering a product is only a portion of the solution here— the rest of it is providing support to your customers around these releases. What types of services does Dell offer to support its data storage products?

Optimal Membrane Switch Design

An overview of some conventional flexible membrane keypads and some unique ways of implementing them in your application.

Alan Atkinson VP of Dell Storage

A conversation about Dell Compellent's

by Michael Lyons, NXP Semiconductor groundbreaking solution and how it will revolutionize data centers.

I

We have full professional services, which are one of the service leaders dating back from the Perot acquisition forward. As far as regular support, I think our copilot, which is the compellent support for our organization, is generally recognized as the best in the class support product.

We don’t metric our folks on how many cases they close a day or by quantity.

They really will stay on the phone with the customer as long as it takes—they’re

n designs that use LEDs, shifter registers can be very useful.

For instance, if the system includes a seven-segment display, a single indicator, or an array of LEDs that form a grid or panel, a standard 8-bit shift register can be used to allow a low pin-count microcontroller to drive multiple LEDs.

Using Shift Registers in LED Designs

How shift registers can be used in LED designs to drive multiple LEDs and reduce the size and BOM of your project.

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Mounted LED Concerns Sheer stress, vibration, or shock can take a toll on another part of the screen printed membrane keypad. Many membrane keypads incorporate surface mounted LEDs within the membrane sandwich. Printed silver circuits and polyester cannot tolerate soldering temperatures. LEDs are attached to the printed silver circuits with a small amount of silver-filled conductive epoxy.

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In a perfect world, attaching and connecting LEDs to printed silver circuits with conductive epoxy sounds like a good idea. However, one of the inherent problems with polyester film used in flexible membrane switches is that the peel strength adhesion of hard coat texture inks, graphic ink, or silver-filled ink for circuit conductors is less than desired.

Figure 2: Standard membrane switch stack-up.

16

LED failures can occur when stress fractures transpire between the silver ink and the polyester at the LED location or along the silver ink conductor next to the LED. The failure starts to occur as a stress crack which may not cause an open circuit right away. When additional stresses are applied during temperature excursion, shock, vibration, intermittent, open circuits can develop causing the LED to be inoperative. Unfortunately there is no practical repair option.

These LED failures can occur even when the flexible membrane is mounted to a metal support plate. Imagine the reliability problems that can be initiated when LEDs are mounted in unsupported

34

MIXINGRTZ SIGNALS:

41

An Introduction to

PID

Return to Zero Comic

flexible membrane keypads. Unsupported keypads are easily stressed during handling when removed from the shipping box, inspected, inventoried, and kitted for an Original Equipment Manufacturer (OEM) assembly line. Applied stresses may not cause any immediate problems. Most stress related LED problems do not show up until the product is in the customer’s hands. The later the failure is detected, the higher the total cost is to repair or replace.

Flexible membrane keypads include a flex tail that is part of the same polyester sheet that contains the circuit conductors in the polyester/adhesive keypad sandwich.

Creasing, tearing, abrasion or vibration can easily damage the flex tail or the termination point at the end of the tail. The total length of the keypad flex tail plus the size of the keypad itself is constrained by the maximum size of the printed polyester sheet that can be printed.

Solution: Transition to Rigid PCB The best solution involves replacing the parts of the keypad design that caused the problems instead of working around the problems. Epec Engineered Technologies has decades of design and assembly experience with replacing the layered flexible printed membrane with a very thin printed circuit board usually about 0.5 mm (0.020 inches) thick (see figure 3).

CONTROLLERS

Identifying the Problem

The intent of discussing these problems is to identify the cause of the failures and find a solution. Without knowing the cause of the problem, finding a permanent solution is more difficult. If a part does not stick well to another part, the solution may not be more adhesive. This is a classic engineering materials problem looking for a better solution.

S

The printed circuit board is mounted to the metal support plate with high performance acrylic adhesive, similar to a layered flexible membrane keypad.

The thermal coefficient of expansion of the printed circuit board laminate is a better match to the metal support plate compared to the polyester/adhesive sandwich. Temperature excursion, shock, and vibration do not cause delamination with the printed circuit board keypad.

Figure 3: High reliability membrane switch with backed rigid printed circuit board.

{Part 1}

The printed circuit keypad assembly can be completed with a graphic overlay, molded rubber keytops, or molded plastic keytops the same as with a printed membrane keypad. The total thickness of the assembly is unaffected as the thin printed circuit board is almost the same thickness as the layered polyester/adhesive.

ince the early 1900s, PID compensators have been one of the most widely used closed loop controllers in industrial applications. However, the tuning of such controllers is widely considered a difficult art. Talking with anyone who is familiar with tuning often quickly leads to a very distressing discussion about poles, zeros, and margins which Visit:inclined eeweb.com makes the casually engineer either stop or, if they are feeling brave (i.e., deadlines

“Most stress related LED problems do not show up until the product is in the customer’s hands.”

3

PULSE Single Phase Fan Predriver Here is a look back of the Allegro’s single phase fan pre-driver released last 2008. The A4930 reduces external component count and incorporates all the key features required for high-current fans. It is designed for pulse width modulated (PWM) current control of single phase brushless fans. It provides internal synchronous rectification control circuitry to improve power dissipation in the external MOSFETs during PWM operation. The device also has internal circuit protection features such as thermal shutdown with hysteresis, rotor lock, and dead time protection...Read More

ARM Processors in a Mixed Signal World There are many types of ARM Processors and the best way to understand the whole ARM processor family is having it classified by application. ARM Processors provide scalable performance, real-time response and configurable features with dual-core options boosting energy efficiency. Recent IC Insight reports highlights the growing market shared by 32-bit microcontrollers, especially ARMbased microcontrollers. 32bit MCUs are much higher returns than other MCUs in terms of sales. It also acquires 20% unit volume growth higher than 8/16-bit MCUs...Read More

Medical Grade 320W Power Supply The MMK320S-24 from Astrodyne is a medical grade, 320 Watt, Enclosed Switching Power Supply that guarantees an output voltage of 24 V. This device has an output current of 12.5 A and operates at a frequency range of 47-63 Hz. It also has 0.8 efficiency and operates at temperature range of -25 to +85 degrees Celscius. For safety purposes, the device is equipped with an over temperature protection, over current protection and over voltage protection...Read More

New 100G Optical Transceivers Introducing Avago Technology’s new generation of 100G optical transceiver module solutions, 100G QSFP28 SR4 and 100G CFP4 LR4. These devices are designed for modern datacenter and enterprise networking applications. The 100G QSFP28 SR4 will be demonstrated using live traffic streams of 100GbE data transmitting over a 100m OM4 optical fiber cable. According to Philip Gadd, vice president and general manager of the Fiber Optics Product Division at Avago Technologies, Avago is now expanding on their broad portfolio of 100G optical transceiver module solutions...Read More

Low Power CMOS AD Converters The CS5505/06/07/08 family of low-power CMOS analog-to-digital (A/D) converters are ideal for measuring low-frequency signals representing physical, chemical, and biological processes. The CS5507/08 family members have single-channel differential analog and reference inputs, and the CS5505/06 members have four pseudo-differential analog input channels. The CS5505/07 family provides a 16-bit output word.

The CS5506/08 provides a 20-bit output word. The CS5505/06/07/08 family samples upon command up to 100 output updates per second...Read More

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FEATURED PRODUCTS High Current Air Core Inductors The new high frequency, high current power inductors offers offers excellent Qfactors of up to 230 at 400 MHz. It can handle current of up to 57 A with inductance values from 22 to 257 nH. The VS Series is offered in three sizes/configurations. The 1010VS measures 10.0 X 10.0 mm, with a maximum height of 6.10 mm. It is available with five inductance values between 23.5 and 146 nH, current ratings up to 26.0 Amps, and Q factors as high as 150. The 1212VS measures 12.0 X 11.5 mm with a maximum height of 11.3 mm...Read More

Power Supply Solution Products Digi-Key Corporation announced a global distribution agreement with XP Power, a power-solution leader offering the widest range of power products available from one source. XP Power is one of the world’s leading developers and manufacturers of power supply solutions for the electronics industry, continuously updating their product range to provide leading-edge power supply technology. This constant refreshing of their product line assures customers that they can source the newest, most cost-efficient products on the market...Read More

Highly Efficient Quad MOSFET Excessive heat generation in high-definition, compact active bridge applications such as network cameras can cause image quality issues. Similarly, thermally induced noise can affect the system’s image sensors which can also degrade the camera’s picture quality. The typical heat sinking solution to regulate thermal fluctuations can further complicate these intricate designs with an added component count and cluttered board space. Fairchild Semiconductor’s FDMQ86530L 60V quad-MOSFET provides designers with an all-in-one package to help with these critical design challenges...Read More

1 Mbit FRAM with I2C Interface Fujitsu Semiconductor announced the developed of a new FRAM product, the MB85RC1MT, with 1 Mbit of memory, the highest memory density of the company’s products with an I2C serial interface. The new product is available in sample quantities starting today. The new product is guaranteed for up to 10 trillion read/write cycles, and is optimum for use in applications requiring frequent rewriting of the data, such as real-time data logging for factory-automation, metering , and industrial equipment. Now with the broad range of lineup for both the I2C and SPI serial interface products...Read More

Digital RGB Light Sensor The ISL29124 is an advanced digital red, green, blue (RGB) color light sensor having low power and high sensitivity. It is incorporated with an I2C (SMBus compatible) interface. The device’s leading photodiode array is providing an accurate RGB spectral response and excellent light source to light source variation (LS2LS). ISL29124 has IR blocking filter to reject IR in light sources, allowing the device to operate in environments from sunlight to dark rooms. The integrating ADC rejects 50Hz and 60Hz flicker caused by artificial light sources. A selectable range allows the user to optimize sensitivity suitable for the specific application...Read More

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PULSE ZMotion Detection and Control Family The Zilog’s ZMOTION Detection and Control Family is a product that provides the improvement of sensitivity and stability over traditional designs. It has a high performance eZ8 CPU core and flexible clocking scheme. It comes with an on-chip analog comparator and full duplex UART of which are some of the key features of the microcontroller. Zilog’s ZMOTION Detection and Control Family of product provides an integrated and flexible solution for motion detection applications based Passive Infrared (PIR) technology...Read More

Fast Curing Epoxy System The Supreme 3HTND-2GT is a one part, high performance epoxy system that features fast curing perfect for glob top and die attach applications as well as bonding and sealing. It is a multifunctional epoxy system that has a large array of remarkably suitable features such as no mixing, a convenient viscosity, sterling physical properties and very fast cures. It can be applied immediately and effectively to a specific area. This epoxy combines excellent electrical insulation properties and thermal conductivity with top-notch dimensional stability and the capability of withstanding rigorous thermal cycling and shocks...Read More

Power and Space Management IC Space is always an important factor in cars, and with the dashboard being one of the most important part of the vehicle, it is necessary to have the most advanced design possible that can be employed in it. Maxim has just released two new products that promotes space-saver feature and more efficient design in the field of automobile design. Whether design teams are trying to cram more features and functions into dashboards or striving to increase efficiency, design groups want chips that save space and reduce weight...Read More

433 MHz ISM Band FSK Transmitter IC The TH72011 is a Frequency-Shift Keying (FSK) transmitter with single ended RF output and a full integrated PLL stabilized VCO integrated circuit. It has high FSK deviation that is possible for wideband data transmission. It has an on-chip low voltage detector and a very low stanby current. The TH72011 is an FSK transmitter integrated circuit designed to operate for applications in 433 MHz European industrial-scientificmedical (ISM) band, according to EN 300 220 telecommunication standard. But this integrated circuit can also be available to other countries who uses the similar frequency band...Read More

Full-featured 802.11 b/g Wi-Fi Module The RN131 is an 802.11 b/g wireless LAN module with ultra-low power design suitable for battery powered applications. With its small form factor and extremely low power consumption, the RN-131 is perfect for mobile wireless applications such as asset monitoring, GPS tracking, and battery sensors. The device has a complete ultra low power embedded TCP/IP solution. The combination of ultra-low power and the ability to wake up, connect to a wireless network, send data, and return to sleep mode in less than 100 milliseconds...Read More

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FEATURED PRODUCTS Wide Input Constant Current LED Drivers The LDB24-xx is a series of Wide Input DC/DC Constant Current LED Drivers that offers seven models available now on the market. These has an input voltage range of 9.0 ~ 36.0 Vdc and output voltage range of 14.0 ~ 48.0 Vdc. With an output current accuracy of ±5.0 %, the devices have efficiency of 95 %. All models in the series comes up with PWM and analog dimming control...Read More

68 MHz I2C Programmable Oscillator The I2C-OSC board is an 8-pin CMOS 1 kHz – 68 MHz Programmable Oscillator device using I2C bus. There are no external components required. Only two signal lines SDA and SCL plus supply voltage and ground are required to be connected.

This makes it perfect for embedded systems that require programmable oscillator.

This board features innovations that set it apart from other programmable oscillator module. Innovations feature like on board I2C address jumpers, pull-up resistors, and power LED...Read More

High Isolation DC-DC Converters Murata announced the MGJ2 series of 2 Watt high isolation dual output DC/DC converters from Murata Power Solutions. These compact encapsulated devices are suitable for powering “high side” and “low side” gate drives in bridge circuits using insulated-gate bipolar transistors (IGBTs) and MOSFETs. Offering basic and supplementary insulation, with an isolation test voltage of 5.2 kVDC and conforming to the internationally recognized safety standard UL60950 (pending), the MGJ2 series can provide a key element of the end-product’s safety insulation system...Read More

Single Inverter with Open-Drain Output The 74AXP1G06 is a single inverter with low power consumption and has an opendrain output. The Schmitt-trigger action on the input of this device makes the circuit tolerant of slower input rise and fall times. The 74AXP1G06 provides very low static and dynamic power consumption across the entire VCC range from 0.7 V to 2.75 V. It is fully specified for partial power down applications using IOFF. The IOFF circuitry disables the output, preventing the potentially damaging backflow current through the device when it is powered down...Read More

Hi-Speed USB Host Controller The SAF1760 is Universal Serial Bus (USB) host controller having a generic processor interface. The device incorporates an Enhanced Host Controller Interface (EHCI), a Transaction Translator and three integrated Hi-Speed USB transceiver that support high-speed, full-speed and low-speed modes. The host controller and the three transceivers of the SAF1760 are compliant with Universal Serial Bus Specification Rev. 2.0. The EHCI part of the SAF1760 is established from Enhanced Host Controller Interface Specification for Universal Serial Bus Rev. 1.0...Read More

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PULSE Accurate Isolated LED Drivers Power Integrations introduced its new family of isolated LED Drivers.

LYTSwitch™-2 delivers an accurate output power of up to 12 watts and significantly minimizes component count, producing a simpler, smaller and more reliable LED lighting design. LYTSwitch-2 LED-driver ICs use primary-side control, resulting in cost-effective, single-sided PCBs with low component counts. In addition, driver isolation allows the LEDs to be affixed directly to a metal heat sink, avoiding the added expense of an electrically isolating enclosure that is often required for non-isolated drivers...Read More

150 Watt DC-DC Converters Power-One’s K Cassettes are a broad and flexible group of power supplies delivering high efficiency and reliability, low output voltage noise and excellent dynamic response to load/line changes, plus wide input voltage ranges of 8 to 385 VDC. They can readily provide up to 150W of power over one or two outputs that offer SELV, no load, overload and short circuit-proof protection. The K Series is equipped with a suppressor diode as well as input fuse and a symmetrical input filter that protects the system from high input transient voltages...Read More

8-bit 2-channel DAC with Buffer The R2A20162 is an 8-bit, 2-channel DAC with buffer that is very small in size package line up and +/-0.7 LSB guaranteed differential nonlinearity error. It has a high output current capacity and 10-bit serial data transfer format. The R2A20162 is an integrated circuit semiconductor of CMOS structure with 2-channels of built-in DAC with output buffer op-amps. It is the electrical characteristic improvement version of the M62342. Serial data transfer type input can easily be used through a combination of three lines: DI, CLK, and LD...Read More

Portable Spectrum Analyzer DSA1030A is a portable spectrum analyzer with small size and light weight and its outstanding performance can satisfy most of radio frequency applications. The digital IF technology enables exceptional system performance and stability. In addition, the wide-screen display, innovative parameter icon layout and user-friendly designs ensure easy and fast spectrum measurement. The DSA1030A is guaranteed to have advanced performance and stability. The DSA1030A operates at frequency range of 9 KHz to 3 GHz awith a frequency resoltuion of 1 Hz...Read More

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FEATURED PRODUCTS H-Bridge Motor Driver The BD6360GUL is a lens driver that It provides 2 Full-ON Drive H-bridge channel. It was developed specifically for stepping motors in auto focus and zoom applications, in parallel interfacing function. The parallel interface requires just a control signal from the microcontroller in order to drive the motor. The gadget is offered in a ultra small functional lens framework for auto focus or zoom system purposes using a stepping motor. This driver integrates a power supply and wave-shaping circuit for the photo-interrupter necessary in order to determine the location of the motor...Read More

2-Pole Ceramic Gas Discharge Tubes TE Circuit Protection 5 mm, 2-pole GDTs (ceramic gas discharge tubes), are commonly used to help protect sensitive telecom equipment such as communication lines, signal lines and data transmission lines from damage caused by transient surge voltages that typically result from lighting strikes and equipment switching operations. Raychem Circuit Protection GDTs offer a high level or surge protection, low capacitance and a broad array of breakover voltage levels, making them suitable for applications such as MDF (Main Distribution Frame) modules, high data-rate telecom applications (e.g. ADSL, VDSL), and surge protection on power lines...Read More

IO Link Compliant HV Line Driver The ZIOL2211 is a single channel high voltage line driver containing a wide range of configurable feature set with a nonvolatile storage of system configuration. It has an excellent electromagnetic compatibility (EMC) performance due to adjustable output slew rate control with a low RDSon of only 6.6 立. The ZIOL2211 is a line driver/level shifter IC containing an HV I/O channel (high voltage: max. power-supply/signal swing = 36V) having a wide range of configurable system features. It addresses the physical layer of sensor/actuator systems in factory automation and is especially designed to support the communication standard IO-Link...Read More

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TECH ARTICLE

MIXING SIGNALS: An Introduction to

PID CONTROLLERS {Part 1}

by Sree Harsha Cypress Technologies

S

ince the early 1900s, PID compensators have been one of the most widely used closed loop controllers in industrial applications. However, the tuning of such controllers is widely considered a difficult art. Talking with anyone who is familiar with tuning often quickly leads to a very distressing discussion about poles, zeros, and margins which makes the casually inclined engineer either stop or, if they are feeling brave (i.e., deadlines closing in), tune the loop intuitively.

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11

PULSE Most of the time, tuning the loop directly on the real system will give favorable results if done carefully and, very happily, a whole lot of math can be ignored. This is almost exclusively the reason why mathematical tuning still remains a less popular method among engineers. This will be a series of articles which I hope will demystify most of the math without being too dry.

A lot of this material is heavily based off of my discussions with Ross Fosler, who I owe most of my practical knowledge in control theory.

Why PID? To begin with, why do we need PID controllers? Yes, yes the textbooks all say that you need them and then give a rather generic diagram similar to the one below:

Figure 1. A generic plant

“In short, we need a mathematical model which can accurately describe the plant characteristic to be able to design a controller which can meet our criteria of overshoot, speed of rejection, and so on.�

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TECH ARTICLE But, in a real world, where do we need them? For example, consider a simple room temperature controller. It can either switch ON to heat the room or switch OFF. The regulator in this case is a simple ON-OFF or Hysteric controller. Since we aren’t too picky about the temperature being a few degrees off, this type of controller works quite well (Figure 2).

Figure 2.

A simple hysteric controller

Now, say we want a more consistent temperature and have a heating element which can control the amount of heating smoothly; i.e., we have more than just an OFF and ON state. This might be a PWM or some other form of input whose magnitude dictates how much heating is produced by the element.

Figure 3.

Basic Increment/ Decrement Rule

Figure 3 shows a very simple set of rules which can be coded into any generic microcontroller to get this done. We can even throw in a small tolerance band to make the controller smooth around the desired temperature.

Upon close examination, this flow chart is pretty vague and ‘Increment Control Signal’ can mean either increment by 1% or 10%. Additionally, we know that just because we switch ON the heating element, the temperature doesn’t change instantaneously. In essence, our room has an associated ‘Plant Characteristic’ to it. Trying to change the temperature very fast will just lead us to overshoot or undershoot the required room temperature.

Figure 4.

Fast Increment vs Slow Increment

With a little trial and error, however, we will be able to arrive at a point where we can trade-off between how fast the temperature reacts with the amount of overshoot we can tolerate. This works out great for simple systems but sometimes plant characteristics can be nasty.

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PULSE For example in Figure 5, the last case is a particularly interesting one, where the plant initially swings in the reverse direction you want to control! Trying to control such systems with a simple rule set can turn into a nightmare for the engineer dealing with it.

In theory, the generic rules associated with the simple increment/decrement rule can work with any system as long as your desired setpoint is a DC value. Only, that the speed at which you reach the desired settling point might be much slower than what you actually need. This is a key point given that rejecting disturbances is fundamental to all closed loop systems.

For example, a voltage spike due to a sudden variation in the input voltage or a sudden drop in load can be unacceptable beyond a short period for the devices powered by it.

Figure 5: Some typical Plant Characteristics

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In short, we need a mathematical model which can accurately describe the plant characteristic to be able to design a controller which can meet our criteria of overshoot, speed of rejection, and so on. Specifically, the above two terms are more formally called as Phase Margin and Bandwidth.

In addition, being able to design a controller on paper will provide an excellent starting point on what the control parameters and will save a whole lot of time spent on tweaking the PID loop.

In part two, I’ll show how to understand plant characteristics using Bode Plots and specifically how to associate a plot with its time response.

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PULSE

Optimal

Membrane Switch Design For High Reliability Applications

By Paul Knupke Epec Engineered Technologies

16

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TECH ARTICLE

O

ne style of low-profile keypad assembly is the conventional flexible membrane keypad

where the switch circuitry is screenprinted. Silver conductive polymer inks are printed onto 1.25 mm (0.005 inches) polyester sheets. Two opposing polyester circuit layers are separated by a thin adhesive/polyester layer with a hole at the switch location. Finger pressure at the switch location deforms the front circuit layer through the spacer hole and completes the circuit to the bottom circuit layer. Tactile feel is provided by a metal snap dome or an embossed dome formed in a polyester sheet, sometimes called poly-domes.

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17

PULSE

S

ince the flexible printed membrane switch assembly is a polyester sheet and layered adhesive, the switch assembly is not self-supporting and must be mounted to a rigid support.

A common support is a flat metal plate such as aluminum. Large dimension flexible printed membrane switch keypads mounted to metal plates are common in the industry. Larger membrane switches with metal plates can suffer performance and construction integrity problems when used in less than ideal environments.

Performance and Construction Integrity Problems These problems are generally related to engineering materials selection. Flexible screen printed membrane keypads are all based on polyester sheets with printed silver conductors (See figure 1).

Polyester is the only common plastic film that has the physical memory to

Figure 1: Screen printed polyester membrane switch with silver conductive ink.

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return to its natural position after finger pressure is applied, released to close, and open the switch contact surfaces. Other than polyester, common plastic films will permanently deform after repeated operation and will not return to the normal open switch position when finger pressure is removed. Polyester is universally used for screen printed flexible membrane switches because it is the only material that works correctly. The pressure sensitive adhesive used in membrane keypads is acrylic adhesive but there are different acrylic adhesives that can be used. Each acrylic adhesive group has its own characteristics based on performance and cost usually aligns with performance. The lower cost acrylic adhesives are used only for the least expensive. The lowest performance keypads used in “throw-away� applications where life and environmental performance are traded for lower cost.

TECH ARTICLE “Other than polyester, common plastic films will permanently deform after repeated operation and will not return to the normal open switch position when finger pressure is removed.�

Even the best designed and manufactured flexible screen printed membrane keypads can have problems when mounted to metal support plates where the keypads and metal plates have large dimensions.

The culprit is the difference in the thermal coefficient of expansion between the plastic/adhesive membrane keypad sandwich and the metal support plate.

With higher or lower temperature excursions from room temperature the difference in expansion rates causes sheer stress at the interface between the membrane keypad’s rear mounting acrylic adhesive and the metal plate.

Acrylic adhesive has better peel strength performance than sheer strength.

Repeated stress cycles can cause delamination between the membrane keypad and the metal support plate.

Once the delamination starts, there is no practical solution or repair.

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PULSE Mounted LED Concerns Sheer stress, vibration, or shock can take a toll on another part of the screen printed membrane keypad. Many membrane keypads incorporate surface mounted LEDs within the membrane sandwich. Printed silver circuits and polyester cannot tolerate soldering temperatures. LEDs are attached to the printed silver circuits with a small amount of silver-filled conductive epoxy.

In a perfect world, attaching and connecting LEDs to printed silver circuits with conductive epoxy sounds like a good idea. However, one of the inherent problems with polyester film used in flexible membrane switches is that the peel strength adhesion of hard coat texture inks, graphic ink, or silver-filled ink for circuit conductors is less than desired.

Figure 2: Standard membrane switch stack-up.

LED failures can occur when stress fractures transpire between the silver ink and the polyester at the LED location or along the silver ink conductor next to the LED. The failure starts to occur as a stress crack which may not cause an open circuit right away. When additional stresses are applied during temperature excursion, shock, vibration, intermittent, open circuits can develop causing the LED to be inoperative. Unfortunately there is no practical repair option.

These LED failures can occur even when the flexible membrane is mounted to a metal support plate. Imagine the reliability problems that can be initiated when LEDs are mounted in unsupported

20

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TECH ARTICLE flexible membrane keypads. Unsupported keypads are easily stressed during handling when removed from the shipping box, inspected, inventoried, and kitted for an Original Equipment Manufacturer (OEM) assembly line. Applied stresses may not cause any immediate problems. Most stress related LED problems do not show up until the product is in the customer’s hands. The later the failure is detected, the higher the total cost is to repair or replace.

Flexible membrane keypads include a flex tail that is part of the same polyester sheet that contains the circuit conductors in the polyester/adhesive keypad sandwich.

Creasing, tearing, abrasion or vibration can easily damage the flex tail or the termination point at the end of the tail. The total length of the keypad flex tail plus the size of the keypad itself is constrained by the maximum size of the printed polyester sheet that can be printed.

Identifying the Problem The intent of discussing these problems is to identify the cause of the failures and find a solution. Without knowing the cause of the problem, finding a permanent solution is more difficult. If a part does not stick well to another part, the solution may not be more adhesive. This is a classic engineering materials problem looking for a better solution.

“Most stress related LED problems do not show up until the product is in the customer’s hands.”

Solution: Transition to Rigid PCB The best solution involves replacing the parts of the keypad design that caused the problems instead of working around the problems. Epec Engineered Technologies has decades of design and assembly experience with replacing the layered flexible printed membrane with a very thin printed circuit board usually about 0.5 mm (0.020 inches) thick (see figure 3).

The printed circuit board is mounted to the metal support plate with high performance acrylic adhesive, similar to a layered flexible membrane keypad.

The thermal coefficient of expansion of the printed circuit board laminate is a better match to the metal support plate compared to the polyester/adhesive sandwich. Temperature excursion, shock, and vibration do not cause delamination with the printed circuit board keypad.

Figure 3: High reliability membrane switch with backed rigid printed circuit board.

The printed circuit keypad assembly can be completed with a graphic overlay, molded rubber keytops, or molded plastic keytops the same as with a printed membrane keypad. The total thickness of the assembly is unaffected as the thin printed circuit board is almost the same thickness as the layered polyester/adhesive.

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21

PULSE Additional Benefits of Using a Rigid Circuit Board in Your Design 1. Additional electronic parts can be incorporated into the keypad assembly.

2. Surface mounted LEDs can be directly soldered to the printed circuit board, thereby eliminating potential intermittent or open LED circuits caused by stress.

3. Keypad interconnections to the application’s electronics are greatly expanded as a wide variety of connectors can be soldered on the rear surface of the printed circuit board through cutouts in the metal support plate.

4. Connectors can be high density, through-hole, surface-mounted, polarized, latching, or shielded.

5. Electronic components such as resistors, capacitors, diodes, and even integrated circuits can also be mounted to the rear side of the printed circuit.

Determining Cost Now that doors of keypad design latitude have been open with expanded selection of electronic components offering reliable soldered electrical joints and much greater reliability, we can look at the last major benefit—cost.

A single printed circuit board replaces several labor intensive manufacturing steps in manufacturing flexible printed membrane keypads. Each of the polyester layers require at least one screen printing operation for the conductive silver ink and generally another printing operation for UV dielectric on the flex tail.

Each polyester printed sheet requires profiling the shape of the keypad and flex tail by steel rule die cutting, knife cutting, or laser cutting. The spacer layer between the polyester circuit layers also requires cutting. Finally, the polyester circuit layers and the spacer layer need to be assembled and laminated together.

Compared to the material and labor needed to fabricate the layered polyester/ adhesive membrane, the printed circuit board is no more expensive and usually less expensive.

“A single printed circuit board replaces several labor intensive manufacturing steps in manufacturing flexible printed membrane keypads.”

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TECH ARTICLE “The improved reliability using a thin printed circuit board in keypads allows the improved user interface keypad to be used in high reliability and harsh environments with improved overall system design, without increasing the cost.�

Summary In summary, the causes of poor reliability in conventional flexible silver printed membrane keypads have been identified and a good solution has been advanced.

Along with solving the initial reliability problem of flexible printed membrane keypads in mundane environments, using a thin printed circuit board in place of the layered printed polyester/ adhesive provides vastly improved interconnection choices.

Figure 4: Membrane switch with rigid printed circuit board stack-up.

Incorporating other electronic components in the keypad is also comparable or lower total cost. The improved reliability using a thin printed circuit board in keypads allows the improved user interface keypad to be used in high reliability and harsh environments with improved overall system design, without increasing the cost.

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PULSE

Dell Compellent

Enterprise-class

Performance at the Price of Disk

Interview with

Alan Atkinson

VP & GM of Dell Storage

26

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INTERVIEW

D

high-performance, low-latency, flash storage solutions for virtually any demanding application. price advantage over traditional solutions and performance at the enterprise level.

With technologies evolving at a rapid rate, Dell Compellent’s storage solutions have simplified scalability to adapt to the ever-changing demands of the industry.

EEWeb spoke with Alan Atkinson, Vice President and General Manager of Dell Storage, about their unique approach to product development, how the changing demands of data centers will influence product design, and how Cloud computing will revolutionize the storage industry.

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PULSE

What is Dell’s approach to providing flash storage products to customers?

We really went at it a different way. We asked ourselves; what if you were able to offer flash at a price where you could take all of your data and put it on flash because that’s what a majority of our customers say they want? The problem is they can’t afford it, so we just couldn’t justify the economics of it. The end goal for our new product was to break the price barrier in the industry—that doesn’t necessarily mean that we would be the fastest, but we definitely had performance targets that we wanted to hit. We ended up with a way to let the user put 100% of their data on flash.

That’s a very different approach than I’ve seen other vendors take and I think that’s a unique thing for Dell.

If you think about Dell’s pedigree, disrupting the economics of the data center is kind of our sweet spot. Our latest data center disruption is called Fluid Cache. This will essentially be a PCIe NAND offering that’s pretty

differentiated, but that will actually target high-end applications—however, this won’t be the majority of what it will be used for. What we want to do is let you get there if you need to get there, but we also want to be able to offer a usage for flash that’s much broader than what is out there now.

How is this solution unique in the industry?

We saw other vendors coming out with technologically uninteresting products; they essentially do what you would expect them to do—but what most of the other vendors have gone after is speed.

We have also seen some vendors go after some specialized workloads, like cloud and QLS—and that’s all fine. But what we really wanted to do was leverage the technology that we had with the Compellent and EqualLogic install base and really go after that larger market.

I have yet to meet a customer that wouldn’t like to have flash instead of disk if they could afford it. We saw that as a market opportunity because nobody was going after that area and mostly because to date, the only way to deal with the cost of better flash was to apply technology you need to for compression or those

“What if you were able to offer flash at a price where you could take all of your data and put it on flash because that’s what a majority of our customers say they want?”

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INTERVIEW “We came up with what I think is a very clever software implementation that allowed us to utilize types of flash that had previously not been used for enterprise storage. ” type of things; which are all fine, but they come at a tradeoff of either performance or CPU horsepower to do that. We came up with what I think is a very clever software implementation that allowed us to utilize types of flash that had previously not been used for enterprise storage. In doing so, we were able to get to the price performance level that we wanted, and to date, no one has been able to match us.

Data centers are very dynamic in that they have needs that change all the time from the customers.

How are you staying in sync with these trends?

It’s interesting—the data center is probably more dynamic than anything I’ve seen since the migration away from the mainframe in the early ‘90s.

On one hand you have your traditional IP, and that discussion hasn’t changed all that much. I would say there’s more focus on power and cooling, but it’s not a radically different conversation.

Of course, the advent of virtualization has really driven realization much higher than it’s traditionally been.

You start to see bottlenecks move to places like storage. Then you start to see a lot of interest in efficiencies with the virtualization of networking and storage and you start putting PCIe and NAND together, which brought networking and storage closer together.

Dell Compellent SC2000

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PULSE Those are some of the trends in the traditional data center, but I think the more dynamic part of data centers— which is still relatively small but growing very rapidly—is what software defined for a data center. For example, private clouds that could be implemented as a private cloud or just more of a traditional type of on-demand service. That side of the world is very interesting. They tend to like very uniform footprints; they typically deploy things as pods so they become these sorts of building blocks and have dynamic workload changes applied with them. That’s an area we’re pretty excited about because we have a strong presence in server, storage, and networking—all three as well as services and software. We think that gives us a pretty unique advantage.

We try to put together solutions because in that part of the storage world, you don’t have to buy the traditional big storage array, top of the rack switch, a core switch, and so on. It’s a different type of architecture and we think we’re very well positioned there. It’s also an emerging technology, so if you were to compare dollars, you’re going to have a relatively small expenditure in that area.

We spend a lot of time thinking about that space and we’re pretty excited about it.

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As far as talking to the data centers and getting a feel for the things they’re looking for, how do environmentally friendly solutions come into play with data centers?

Well it’s not just storage; it’s our whole power and cooling footprint. In those cases, I think the trends that we’ve seen lately have been around what flash does for the storage environment. In regards to convergence—if you look at our VRTX product, for example—it has been a real game changer in the economics with power and cooling as well. But on the flash side, where we’ve really seen it, it’s not unusual that we can take 6U— ten times more worth of spindles—and collapse them down into 2U of flash.

This is because people aren’t actually using all the data on those spindles and all they really care about is the performance characteristics. As soon as you go to solid state you change that discussion. Again, this is one of those cases where because we got to the current price point, we can now take a lot more spindles out than other vendors can. You can get pretty good rack compression and that obviously comes with a pretty good power and cooling state as well. It’s a lot cheaper not to have to run those motors. We’ve seen that be a pretty interesting benefit of the whole solid-state discussion.

INTERVIEW What types of customers are using Compellent solutions?

We are still early on in the game, but I’m seeing deals go down with financials.

Financials are very keen on this, which makes sense. They’re probably among the most data center constrained and some of the most performance hungry out there for their applications, so that’s not really surprising. We’re also seeing a lot of interested service providers.

Surprisingly, if we were to cross the other side, we’re getting a lot of generalpurpose interest—the kind of customer that is putting out 3 terabytes of storage.

If you look at how our customers buy, they buy a combination of performance and capacity. Just the fact that we’re basically at the price point that we were in May for capacity disks you can now buy, as far as performance disks, you can get 15k if you need. They can now buy flash—it’s just a real differentiator in that general-purpose market. It’s the same people that may have kicked the tires before but now they’re going to buy flash instead of disks.

“If you look at how our customers buy, they buy a combination of performance and capacity.”

Dell Compellent SC8000

Offering a product is only a portion of the solution here— the rest of it is providing support to your customers around these releases. What types of services does Dell offer to support its data storage products?

We have full professional services, which are one of the service leaders dating back from the Perot acquisition forward. As far as regular support, I think our copilot, which is the compellent support for our organization, is generally recognized as the best in the class support product.

We don’t metric our folks on how many cases they close a day or by quantity.

They really will stay on the phone with the customer as long as it takes—they’re

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PULSE proactive either in a box or they’ll perform firmware upgrades, which is an area where we consistently get kudos.

That’s been well before my time at Dell, so that goes back to where Compellent was an independent company. We’ve been taking some of the software that powers that and building them EqualLogic as well. Again we’re spending a lot of time talking about family values, if you will, trying to get sort of the best features of all of our product lines across all of our product lines because why not. We own that IP, so why wouldn’t we do that? That’s an area where we really excel.

How would describe the leadership and culture behind Dell’s flash storage solution?

I think it’s a culture of innovation that goes way back. Tiering was basically invented by a few people at Compellent.

I know that’s been copied a lot and there’s multiple versions of vendors who would still argue they’re best in class, but because of the way we get virtualization tiering, We really took a step back and said what if we rewrote these tiering algorithms specifically for flash—what could we accomplish and how can we really be disruptive? To us, the design goal that really goes after that market was not specialized. We could have done something like: we just want to make the fastest thing out there and we could have probably pulled it off and I think actually on the PCIE NAND side we’re going to make some pretty exciting announcements in that area.

32

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“Flash being the price of disk is really one example of disruptive design.

We’re in the midst of a really exciting time in Dell storage.”

I think we’ve got we really set out to look at a problem that no on else was really going after and figured out a way to do it. I think that’s a really good team effort between marketing guys and the engineers researched it really well. We know people want flash, we don’t know how to get it to them other than selling it at a loss, which isn’t a great business generally so this is something we’re really excited about. So far it’s been going really well for us.

Flash being the price of disk is really one example of disruptive design.

We’re in the midst of a really exciting time in Dell storage. Between August of this year to March 2014, we have 9 product introductions, which is a really remarkable clip of getting products out. They’re all sort of done with that disrupting the data center economic kind of philosophies. That’s not just flash, but that’s also things like the Fluid Cache and also things like data placement at the low end when you really want to optimize capacity size and all through the lens of how can we be disrupting by offering more for less. I think that is the general design philosophy that we have.

INTERVIEW M o v i n g To w a r d s a

David Elien VP of Marketing & Business Development, Cree, Inc.

Clean Energy

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FUTURE

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PULSE

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TECH ARTICLE

Using

SHIFT REGISTERS to Reduce Size and BOM

in LED Designs

by Michael Lyons, NXP Semiconductor

I

n designs that use LEDs, shifter registers can be very useful.

For instance, if the system includes a seven-segment display, a single indicator, or an array of LEDs that form a grid or panel, a standard 8-bit shift register can be used to allow a low pin-count microcontroller to drive multiple LEDs.

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PULSE Figure 1 gives an example. A single 5V 74HC595 shift register, with serial inputs and serial or parallel outputs, provides I/O expansion for the microcontroller. Serial data is applied to the serial input of the 74HC595 and clocked in via the input clock.

Once the 74HC595 is loaded, the output clock applies the data to the storage register and to the parallel and serial outputs. External drivers, controlled by the 74HC595, then activate the corresponding LEDs.

Figure 1. An 8-bit 74HC595 shift register driving multiple LEDs

The ability to cascade shift registers can reduce the total number of microcontrollers needed in the design, and that can help lower costs and reduce size, too.

Figure 2. Cascading 74HC595 devices to drive more LEDs

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Using the 74HC595 for I/O expansion means that it takes only three MCU control pins to drive up to eight LEDs. Reducing the number of control pins makes it possible to use an MCU with a lower pin count, and that can yield a smaller, more cost-effective design.

Also, because the 74HC595 includes a serial output, several devices can be cascaded together. Figure 2 gives the layout.

TECH ARTICLE Now, with the cascading, the same three pins on the microcontroller can be used to control up to 16 or 24 LEDs instead of just eight. The ability to cascade shift registers can reduce the total number of microcontrollers needed in the design, and that can help lower costs and reduce size, too.

Figure 3 gives the output schematic for one such device, the NPIC6C596A LED driver from NXP, which combines shift register functions similar to a 74HC595 with a high-voltage (HV) MOSFET driver.

In some cases, a 5 V, 8-bit register like the 74HC595 can be used to drive LEDs directly.

This works best when the LEDs are specified for relatively low voltage and forward current. LEDs that operate with voltages higher than 6 V or require forward current that exceeds 70 mA will typically require an external driver.

Replacing the 74HC595 with the NPIC6C596A eliminates the need for external drivers, creating a design that is more compact and has a lower bill of materials.

Open-drain Outputs Adding open-drain outputs to the shift register creates a single-chip solution that eliminates the need for an external driver.

This can yield significant reductions in the bill of materials, since each output of the shift register can drive the LEDs directly.

NPIC6C devices have open-drain outputs that are tolerant to 33 V. Each output is designed to sink 100 mA and there is no limit on ground current. All the outputs can actively sink 100 mA simultaneously.

The outputs include current-limiting circuitry, which sets a 250 mA maximum on the sinkable current, and each output also includes thermal protection. Having

Figure 3. Output schematic for shift register with opendrain outputs

Figure 4. Output schematic for shift register with open-drain outputs

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PULSE these protections means the NPIC6C596A device can be used to drive a wider range of LEDs than the 74HC595, including LEDs that operate at higher voltages and with higher forward current.

Protection features Figure 5 shows the behavior of the current-limiting circuitry on the opendrain outputs of the NPIC6596A. The circuitry limits the maximum current each output can sink. As the drain voltage increases, the drain source current decreases. This protects the outputs and the components they are driving. At 25 째C, the output clamp is typically activated when the drain source current is 250 mA.

Figure 5. Current-limiting behavior in NPIC6C596A

Figure 6 shows how the open-drain outputs of the NPIC6C596A provide thermal protection. The clamp current is inversely proportional to temperature.

As the temperature increases, the output resistance increases, thus limiting the drain source current and preventing damage to the output and the components it drives. At 25 째C, the output typically limits the drain source current to 120 mA.

Figure 6. Thermal protection in NPIC6C596A

As the temperature increases, the output resistance increases, thus limiting the drain source current and preventing damage to the output and the components it drives.

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TECH ARTICLE

Multiple Options Table 1 shows the NPIC6C LED drivers available from NXP. The NPIC6C596 and the NPIC6C596A are 8-bit solutions, while the NPIC6C4894 is a 12-bit solution. All include a serial output for cascading. Data is propagated through the shift register on the rising edge of the input clock. With the NPIC6C595 and the NPIC6C4894, the same rising edge is used to clock data to the serial output QS. The NPIC6C596 and NPIC6C596A delay the serial output to the next falling edge of the input clock. The delay provides a longer data hold time, which improves timing margin and makes it easier to cascade many shift registers.

The NPIC6C596 and NPIC6C4894 can be used between 4.5 and 5.5 V, making them suitable for 5.0 V control logic interfaces.

The NPIC6C596A can be used from 2.3 to 5.5 V, so it can be used with 5.0, 3.3, and 2.5 V control logic interfaces. All NPIC6C devices operate from -40 to +125 째C and with an input clock frequency of at least 10 MHz.

The delay provides a longer data hold time, which improves timing margin and makes it easier to cascade many shift registers.

NPIC6C LED drivers from NXP Format

Supply voltage (V)

fmax (MHz)

Tamb (째C)

QS clock

NPIC6C595

8-bit

4.5 to 5.5

10

-40 to +125

Rise

SO16, TSSOP16, DQFN16

NPIC6C596

8-bit

4.5 to 5.5

10

-40 to +125

Fall

SO16, TSSOP16, DQFN16

NPIC6C596A

8-bit

2.3 to 5.5

10

-40 to +125

Rise

SO16, TSSOP16, DQFN16

NPIC6C4894

12-bit

4.5 to 5.5

10

-40 to +125

Rise

SO20, TSSOP20, DQFN20

Type number

Packages

Table 1. NPIC6C LED drivers from NXP

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PULSE Package Suffix

D

PW

EQ

D

PW

16-pin

16-pin

16-pin

20-pin

20-pin

SOTI109-1

SOT403-1

SOT763-1

SOT163-1

SOT-360-1

Width (mm)

6.00

6.40

2.50

10.30

6.4

Length (mm)

9.90

5.00

3.50

12.80

6.50

Height (mm)

1.75

1.10

1.00

2.65

1.10

Pitch (mm)

1.27

0.65

0.50

1.27

0.65

Package

Table 2. Package options for NPIC6C LED drivers

NPIC6C LED drivers are available in industry-standard SO and TSSOP packages, as well as the space-saving DQFN leadless package, which is up to 76 percent smaller than a TSSOP and 40 percent smaller than a QFN. DQFN packages also include a heat sink and are the packages of choice for spaceconstrained applications that use higher currents. Automotive variants are also available.

Conclusion When LEDs are part of the design, shift registers make it possible to use a smaller, less expensive microcontroller. Standard 8-bit shift registers like the 74HC595 are available from a number of suppliers, including NXP. Shift registers that are equipped with open-drain outputs, like the NPIC6C series from NXP, go a step further, because they eliminate the need for external LED drivers. More about the NPIC6C series can be found at http:// www.nxp.com/products/logic/family/ NPIC/#overview.

When LEDs are part of the design, shift registers make it possible to use a smaller, less expensive microcontroller.

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