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Teardown of an (IoT) Wireless Device with Bluetooth Low-Energy and ZigBee

23 Jun 17

The Internet of Things (IoT) is one of the hottest areas of new product development. By 2020 it is estimated there will be 50 billion IoT devices. Since all of the products I design are protected by NDA, I’ve decided to instead show you the details behind a IoT reference design from Texas Instruments (TI) that offers Bluetooth Low-Energy, ZigBee, and 6LoWPAN wireless protocols.

TI’s has developed a IoT reference design they call SensorTag that’s purpose is to showcase their IoT system-on-a-chip called the CC2650.The original SensorTag used TI’s CC2541. The newest SensorTag that is based on the CC2650 is a significant performance improvement over the original version. The CC2650 is built on a much faster 32-bit Cortex-M3 microcontroller, versus the CC2541’s low-speed 8-bit 8051 microcontroller. Also, unlike the CC2541 which only offers Bluetooth Low-Energy, the CC2650 offers ZigBee and 6LoWPAN wireless protocols.

The SensorTag, as its name might imply, is loaded with various sensors including temperature, humidity, pressure, an accelerometer, a gyroscope and a magnetometer.The SensorTag constantly transmits the data from these sensors using either Bluetooth Low-Energy (aka Bluetooth Smart), ZigBee, or 6LoWPAN.

Transceiver Radio & Microcontroller

TI’s CC2650 is known as a System On a Chip (SoC).  It not only includes all of the circuitry for transmitting and receiving data via radio waves (called the transceiver) but it also includes a microcontroller that runs the required protocol stacks (firmware) and interfaces with all of the sensors.

There is a lot of functionality built into that little chip.  It includes a Cortex-M3 32-bit microcontroller which is a very standard, and fairly powerful microcontroller. Not only does the microcontroller control the wireless transceiver but it also can control external components, like sensors, buttons, LEDs, displays, etc. This is because the CC2650 provides up to 31 general purpose I/O lines, various timers, analog-to-digital converters, a battery monitor, and various serial interfaces like I2C (a two-wire serial interface) and SPI.

The full schematic diagram for the SensorTag is available from Texas Instruments.

The antenna

Bluetooth Low-Energy, ZigBee, and 6LoWPAN all use a carrier frequency of 2.4 GHz.  There are two common choices when it comes to 2.4GHz antennas. Either a chip antenna or a PCB antenna. The SensorTag uses a PCB antenna known as an Inverted-F antenna.  A PCB antenna has the advantage of being essentially free because no extra component is necessary. On the other hand a chip antenna can allow a smaller board size. PCB antennas also may require several board revisions to get them to work optimally.

Crystal Oscillators

These generate precise frequency oscillations for timing the microcontroller and communications with the various sensors. Quartz crystal oscillators revolutionized the watch industry decades ago. These oscillators use the piezoelectric effect which is when a crystal vibrates at a frequency proportional to the pressure applied to it. The SensorTag uses two crystals: one at 24 MHz and one at 32.768 kHz.

External Memory Storage

Although the CC2650 includes 128kB of built-in FLASH memory, the SensorTag also includes an additional 512kB of FLASH memory. This extra memory is provided by the W25X40CLUXI from Winbond Electronics.

The Sensors

All of the sensors are microchip based solutions. They all include analog-to-digital converters on-chip allowing them to output data in digital format via the popular two-wire serial interface, I2C.

Accelerometer / Gyroscope / Magnetometer

InvenSense MPU-9250 – The MPU-9250 is a multi-chip module consisting of two dies integrated into a single package. One die houses the 3-axis gyroscope and the 3-axis accelerometer. The other die houses the AK8963 3-axis magnetometer from Asahi Kasei Microdevices.

Hence, the MPU-9250 is known as a 9-axis motion sensing device that combines a 3-axis gyroscope, 3-axis accelerometer, 3-axis magnetometer and a Digital Motion Processor™ (DMP). The MPU-9250 communicates with the primary system microcontroller via either I2C or SPI serial interfaces. I2C (and secondly SPI) are by far the most common communication protocols used by sensors. An accelerometer measures proper acceleration or g-force which is different than measuring the rate of velocity change. For example, an accelerometer will measure 9.8 m/s^2 (1 g) when stationary on the Earth.

This is the acceleration caused by the Earth’s gravity. It’s actually during free fall that an accelerometer will measure zero (0 g). The InvenSense accelerometer can measure up to +/- 16 g’s.

A gyroscope measures orientation along 3-axises. For many products it is critical for it to know which way is up. That’s the function of a gyroscope. A magnetometer measures magnetic field strength, and in the case of the MPU-9250, it measures it along 3 axes. A magnetometer is usually used as a compass, but can also be used for other functions like a metal detector (limited to detecting only magnetic, or ferrous metals).

All of these sensors are created using a technology called Micro-Electro-Mechanical Systems (MEMS). MEMS is a technology that allows super small electro-mechanical devices, like sensors and actuators, to be created alongside the electronic devices on a microchip.

Humidity Sensor

Texas Instruments HDC1000YPA – The HDC1000YPA measures humidity using a capacitive sensor.  A capacitor is a device that stores electrical energy. A capacitor consists of two conductive plates separated by an insulating dielectric material. The dielectric material’s properties are sensitive to moisture causing the capacitance to vary with humidity.  This effect is used to measure humidity.

The HDC1000YPA also includes a temperature sensor that outputs the temperature of the chip itself, instead of a distant object like the next component. Both the humidity and chip temperature are passed to the microcontroller via I2C.

Infrared Temperature Sensor

Texas Instruments TMP007 – The TMP007 measures the infrared energy emitted by an object to determine the object’s temperature. It passes this measurement value on to the microcontroller via either an I2C or SMBus interface. This method allows temperature measurement of an object without the need to ever make physical contact.

Pressure Sensor

Bosch Sensortec BMP280 – This chip measures barometric pressure which can be used for weather forecasting and altitude measurements. It interfaces with the CC2650 microcontroller via either I2C or SPI serial ports. Before a big storm the barometric pressure drops so measuring it is a critical for weather forecasting. Also as you go up in altitude the barometric pressure drops at a predictable rate.

Digital Microphone

Knowles SPH0641LU4H – This is a digital microphone chip known as a MEMS (Micro-Elecrtro-Mechanical-System) device. This microphone gives the SensorTag the ability to transmit audio.

Light Sensor

Texas Instruments OPT3001 – This is a sensor that detects the intensity of visible light. The spectral response of this sensor closely matches the human eye and includes a significant reduction of Infrared (IR) light. The measured light intensity value is sent to the CC2650 microcontroller via the I2C serial interface.

DevPacks

One big improvement made with this version of the SensorTag is the addition of a port for connecting up external devices. DevPack plug-in modules allow you to extend the functionality of the SensorTag by adding features such as display, lighting, capacitive touch, new sensors and much more. You can also design your own packs to interface with the SensorTag via the DevPack port.

Power Management

The SensorTag is powered from a single 3V lithium coin cell battery. It also has the option of adding a AAA battery pack.The original SensorTag used a TPS62730 buck regulator to down convert the 3V battery to only 2.1V. The new version instead powers all of the circuits directly from the battery without any extra internal regulation. A Texas Instruments TPS2291 load switch is placed between the battery and the other circuits so as to provide a controlled voltage ramp up of the supply voltage.

In general, there are two types of voltage regulators – linear, and switching. A linear regulator (sometimes called a Low-DropOut regulator or just LDO) is simple but very inefficient.  They waste lots of energy as heat). They are especially wasteful when the input voltage is much higher than the output voltage, wasting as much as 90% of the input power. The primary advantages of a linear regulator is they generate a very clean output, they’re simple, and cheap. A switching regulator, like the TPS62730 used in the original SensorTag, on the other hand is very efficient, usually only wasting 5-15% of their input power.  However, they are very complex circuits compared to linear regulators.

In simple terms, they work by switching on/off while using an inductor and capacitor as temporary energy storage elements. For example, the original SensorTag had a regulator switching frequency of 2 MHz.

Passives

There are three fundamental electrical components that are used in pretty much all electronic circuits: resistors, capacitors, and inductors.Resistors and capacitors are the most common and even the simplest of circuits use them.

Numerous resistors are used by the SensorTag for set points, voltage dividers, and filtering.  Resistors, as their name implies, resist the flow of current.Also a large number of capacitors are used by the SensorTag for energy storage, filtering, timing, and AC coupling.  Fundamentally, capacitors store energy in the form of an electric field. Inductors aren’t as common, but they are still used in most commercial quality electronic circuits.  Inductors are the cousin to capacitors. They are used for energy storage, filtering, tuning, and timing.  Unlike capacitors, inductors store energy in the form of a magnetic field.

If you would like to learn all of the details to developing a new electronic product be sure to check out my Ultimate Guide on How to Develop a New Electronic Product.
If you found this guide helpful please share it across your social media networks. You’ll find share buttons below. I really appreciate shares!

Author : John Teel
Reference : http://predictabledesigns.com/tear-down-of-a-bluetooth-low-energy-ble-product/

Recent Blogs

20 Nov 17

OrCAD™ Design

I would like to share my views on one of many popular industrial EDA software: OrCAD. This electronic design automation tool is pretty much the standard and is in widespread use in the industry. It is not meant for the hobbyist, as it has a steep learning curve: OrCAD splits up every feature into standalone applications and each feature has its own program.

OrCAD Capture is one of the most widely used schematic design solutions in the world. Because it’s part of the OrCAD PCB Design Platform, it can be purchased as a stand-alone application yet will integrate seamlessly with other OrCAD applications as your needs expand or change. It comes with huge libraries of components; These large libraries are critical because creating new components can introduce errors that won’t be captured by any of the verification tools. That being said, regardless of the package you’ll eventually need to create some custom components yourself. OrCAD handles pin swapping much better than other software like Altium. OrCAD has fast response times to common actions like copy, drag, popup properties etc. It also has very flexible DRC checking. In OrCAD I could mark a pin as NC and it transferred to layout as NC, never popping up as an DRC error for the branch called “unconnected pins”. In Altium, I had to explicitly put a script in query which would mark pins as NC in case I wanted to run NC rule against other pins.

The latest OrCAD Capture version has many new features. The design difference viewer performs logical and graphical comparisons between two designs, two schematic folders or two schematic pages and displays the differences in the form of a portable HTML format. The new advanced annotation feature lets users annotate multiple schematic pages at a time giving them complete control over their component annotation process in the design cycle. OrCAD Capture provides you with the capability to convert Capture designs to XML format and vice-versa based on the requirements. The new PDF export functionality lets users export Capture designs as a PDF file and provides intelligent design information.

OrCAD PCB UI is seriously fast. OrCAD PCB/Allegro has an amazing autorouter. It really works well and with proper placement it does a great job. However, it takes a long time to understand and configure. Basically, you have to configure things like libs, padstacks, etc.. Allegro’s biggest weakness is that it does not have any real library management. Even the place parts option in the PCB has no way of displaying parts or symbols as they call them in logical folders.

Putting these things aside, the true power of OrCAD Allegro really shines when you want to do things like large complex boards or RF design. The shape editing tool in OrCAD/Allegro is amazing for copper pours and copper pour editing. Large copper pours don’t bog down the display either. In Allegro, Automatic length matching works very well. A lot of times it manages to make right length adjustments even in areas where one would think it is impossible. Its 3D rendering falls short, though.

As I had mentioned before, in OrCAD you have different applications for each feature. This is actually really inconvenient as you need to work with a few different windows opened while performing any function. While in Altium, the schematic editor and PCB editor can be accessed and worked on in adjacent tabs. Also, there is scope for alerting and updating changes in one window to other. The panels feature I mentioned in our previous Altium post also needs a special mention here, as it adds more convenience while working, providing easy access to SCH lists, PCB lists, etc.

Both Altium and OrCAD provide wizards to ease new PCB footprint creations. However, the wizard in Altium is more advanced and has more package designs compared to the one in OrCAD. Trying to create PCB footprints for components outside the wizard is similar in OrCAD and Altium just like any EDA software. Still, Altium feels more user friendly regarding shortcuts and number of clicks needed for any action, compared to OrCAD. Getting more into OrCAD might help me find it easier to work on in the future.

One major thing that separates OrCAD from the lower end CAD packages is the PSpice add-ons that allow full circuit simulation. It does have quite a learning curve but if you have it at your disposal, it can save you a ton of time and frustration on some of the more advanced mixed signal designs. There are even entire courses in college focused on just learning how to use this one feature. OrCAD CIS allows you to integrate component information in a database, something that is useful when working in a bigger team with an accelerated design cycle.

By: Tony Jose
References:

  1. http://www.orcad.com/products/orcad-pcb-designer/overview
  2. http://www.orcad.com/products/orcad-pcb-designer/compare
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20 Nov 17

Altium™ Designer 15.1

If you’re getting into circuit design, then these are some of the skills you want to have: Selecting parts, schematizing a working design, thermal management, EMC, managing various constraints, design for manufacture, etc.. If you can place and route a PCB in one design package, chances are it’s not going to be a huge amount of trouble to do it in another package. In this article, I would like to share my views on the most popular industrial EDA software, Altium Designer.

Altium has bit of a learning curve for a newbie, so it might not be as intuitive as KiCAD or Diptrace, but is much better compared to Eagle. However, for someone with experience in creating few PCBs with some other EDA softwares, Altium would be under the belt once you review the basic working and get used to the really impressive User Interface.

Altium’s biggest plus is its UI. Altium has different panels for the schematic library, PCB library, schematic document, PCB layout document, and others which can be easily accessed when working and hidden in tabs on the sides of the window when not.  These tabs can be viewed and accessed just as easily as changing tabs in a browser. This layout provides an ergonomic experience, making it so that users don’t have to keep on switching between windows during designing like they have to other design packages like KiCAD. Altium Designer has a project tab with an intuitive project tree of all the documents in a particular project, which allows easy access to drag and drop files in and out of the project.

The Altium Schematic editor is fairly straightforward and has tons of hotkeys associated with it to make it easy when creating a component with several pins. Most ICs just have a rectangle and pins but if you needed to draw custom shapes, it’s fairly easy to do so. The footprint editor is fairly straightforward as well: It comes with a wizard that walks the user through several different types of packages and does all the spacing for you. The integrated library basically combines the schematic library with the PCB library; Looking through it, we can find the necessary resistors and capacitors needed to build the circuit. They all have the associated PCB footprints built in.

Altium has the ability to outline all the changes in front of the designer, validate them and then execute. It does this with an “ECO” process and it literally lists every single change you’re about to make to the design and displays whether it was successful or not. This may seem like overkill but when you’re moving around the design making changes, it’s a really nice visual check to make sure you’re changing what you want. While creating the PCB and when importing the schematics we get to see every single thing through the ECO process, including the components, NETs, PCB footprints, classes and even the room. Altium has some features to help with routing complex designs.

The 3D modelling in Altium is fantastic. We can bring in models (such as our proposed enclosure) and see how well our PCB fits. We can export the entire board with components and use it to build a case in another software. Or we can import a case into Altium and design the board to fit it. It even does collision detection of the board, case, and components.

Altium has never been cheap, but it now has a product called Circuit Maker which is free, allows unlimited number of components and board size, and has a lot of Altium’s main functionalities. The drawbacks are that it’s in beta and you can only run it on your browser. Altium also has a mid range product called Circuit Studio that is very much like Altium Designer but a bit cheaper. It’s closer to the full designer than circuit maker is. Altium is quickly becoming the industry standard for professionals and the features that are lacking will surely improve as their customer-base and widespread feedback grow accordingly.

By: Tony Jose
References:
1. 
http://www.altium.com/altium-designer/overview
2. https://www.sfcircuits.com/pcb-school/pcb-design-software-comparison-guideac

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23 Jun 17

Bluetooth or WiFi – Which is Best for Your New Wireless Product?

There are numerous wireless standards at your disposal when creating a new product. Each choice has its own set of advantages and disadvantages. It really depends on your goal. In this article we’re going to look at the three most popular short-range wireless standards including: Bluetooth Classic, Bluetooth Low-Energy (BLE), and WiFi Direct.

The Need for Speed

If high speed data transmission is the most critical requirement for your product then most likely WiFi Direct will be the best choice. Everyone has heard of WiFi, but few know of WiFi Direct. Although that is changing.

Standard WiFi requires an access point. So if you want to transfer data from one device to another it must pass through the access point.WiFi Direct has the speed advantages of WiFi without the need for an access point. Data can be transmitted directly from one device to another just like with Bluetooth.

Table 1 – Speed Comparison

WiFi Direct has a maximum data transfer speed about 10x the speed obtainable with Bluetooth Classic.

So, for example, if your product needs to stream video, especially high-definition video, you’ll need the fastest wireless connection possible. There is no way Bluetooth will be fast enough, so you’ll almost surely need to offer WiFi Direct connectivity.At the other end of the speed spectrum is Bluetooth Low-Energy (also called Bluetooth Smart) which is about 2-3x slower than Bluetooth Classic, or 20-30x slower than WiFi Direct. It is typically used for transmitting small amounts of intermittent data, such as sensor readings (temperature, acceleration, etc.) or perhaps GPS coordinates.

When you need to constantly transmit data, such as when streaming audio, you’ll usually need to use Bluetooth Classic. Bluetooth Classic is optimized for streaming applications, versus BLE which is optimized for short, infrequent bursts of data.

However, it is possible to use BLE for streaming audio, but not at the same quality as with Bluetooth Classic. For example, Bluetooth stack provider, Searan LLC can provide you with a custom Bluetooth LE stack that allows audio streaming.

Transmission Range

WiFi Direct has a maximum range of about 200 feet, compared to only about 50 feet typically for Bluetooth (Classic and Low-Energy). The increased range of WiFi Direct is possible because of the higher transmission power used by WiFi Direct. The trade off is battery life and this increased transmission power will drain a small battery much faster than either Bluetooth standard.

Table 2 – Range Comparison

But wait a minute…things aren’t always so simple. There are some exceptions.  First of all, there are actually different classes of Bluetooth transmitters. Most Bluetooth products use a class 2 transmitter with a range around 50 feet as previously stated. But it’s possible to use a class 1 transmitter with a range closer to about 300 feet.  But, just like with WiFi Direct, the higher transmission power comes at the cost of reduced battery life.

By using a range extender circuit (which consists mostly of a very sensitive receiver) you can increase the range with Bluetooth even further. For example, Bluetooth module provider Bluegiga offers a long-range BLE module (BLE121LR) with a range up to around 1,500 feet. They also offer a Bluetooth Classic long-range module (WT41) with a range up to 3,000 feet!

There is yet another exception. In some applications, it’s actually possible for Bluetooth (even the Low-Energy version) to transmit over a larger range than WiFi Direct while still using very little power. This is possible due to an awesome feature called mesh networking.Normally to send data from device A to device C you must form a direct link between A and C. But with mesh networking you can instead send data from device A to device C via device B.

So if device B happens to be halfway between A and C, then A and C can be twice as far apart as normally allowed. This is because device B acts as a relay, or in many ways a signal booster. This idea can be expanded making possible a large network of interconnected, low power devices spread out over a large distance. In fact, up to 65,000 devices may be interconnected using mesh.

A leading maker of Bluetooth microchips called CSR started including mesh networking with their Bluetooth Low-Energy chips in 2014. So far they are the only chip maker to offer mesh with BLE. However, I doubt that will be the case much longer.

There is the option of having a custom Bluetooth stack developed to allow mesh networking with other chips, or with Bluetooth Classic. I know that Bluetooth stack provider Searan has the ability to add mesh networking to their Bluetooth stacks.

Power / Battery Life / Battery size

Higher speed and longer direct transmission range correlate with higher power usage and thus shorter battery life. So if battery life or battery size are important for your product then power usage becomes critical.

Bluetooth Low-Energy (BLE) is the clear winner in regards to low power usage. It was primarily developed for Internet of Things applications which many times need to run from a small, single watch battery. A BLE device can run for a year or two on a single watch battery. This is possible primarily because these types of products are designed to only transmit occasionally. For example, a BLE device may only transmit data for 1 second once per minute. This means the device is idle for 59/60 = 98.3% of the time.

Compatibility

If compatibility with older smart phones is critical for your product, then Bluetooth Classic may be the best choice. All smart phones support Bluetooth Classic, but only moderately newer phones support BLE and WiFi Direct.

Table 3 – Compatibility Comparison

For some applications at times Bluetooth Classic is best choice, and at other times Bluetooth Low-Energy is the better option.  For example, perhaps you prefer Bluetooth Low-Energy to conserve battery life, but you also want to allow compatibility with older smart phones.

The best solution may be Bluetooth Dual-Mode. When communicating with newer phones you could use the battery saving BLE mode, but when you need to link to older phones then you could select Classic mode. Most of the Bluetooth chip makers and module providers offer dual-mode Bluetooth solutions.

Security

All three wireless standards offer a high level of security. However, WiFi uses 256 bit encryption versus Bluetooth (Classic and LE) use only 128 bit encryption. In most cases Bluetooth’s level of security is sufficient, but if security is critical for your product then WiFi Direct may be the better option.

Summary

As is always the case with engineering, there are trade-offs between the various solutions.  No solution is best in all applications.  You need to decide which criteria is most important for your product. This may be simple or complex.  If speed is all you care about then your choice is easy.  Or if battery life is your primary concern then your choice is pretty simple.  But if you care about both speed and power usage equally then your choice becomes more complex.

Deciding which specifications are the most critical for your product is always a challenging aspect of product development.  Welcome to the world of product development where nothing is truly simple. If it was easy, every company would be as successful as Apple.

Author : John Teel
Reference : http://predictabledesigns.com/what-type-of-wireless-is-right-for-your-product-bluetooth-wifi/

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