Category Archives: Guides

LTM2893 μModule isolator for ADCs

Analog to digital converters (ADCs) need to float to the common mode of the input signal to absorb the harsh voltage conditions and transients. The best way to do this is to place an isolation barrier between the ADC and the external signal. Even applications that perform under moderate conditions can benefit from the presence of an isolator. The LTM2893 from Linear Technology provides such isolation, improving on system safety, especially when reading from high-resolution successive approximation register type of ADCs.

Ideally, the isolator for an ADC should be near invisible. Its function would be to manage the control and data signals, maximizing the sampling rate, and minimizing the effects of jitter on the performance of signal to noise ratio. The LTM2893 μModule isolator from Linear Technology meets all the above criteria, achieving these for ADCs with SPI interfaces, offers a 1 Msps range, while supporting a 6K Vrms isolation rating.

Options that are more traditional exist, but provide limited functionality, especially when reading data from high-resolution successive approximation register (SAR) ADCs. Most traditional high speed digital isolators work maximum up to 25 MHz, with a few special devices reaching 40 MHz On the other hand, the LTM2893 can easily read data samples at rates up to 100 MHz. Additionally, it is flexible enough to be able to handle multiple ADCs. This effectively solves timing issues and other limitations of the standard digital isolator interfacing that SAR ADCs face.

Test and process equipment need isolation so that their inputs are not damaged if accidentally misconnected or from overvoltage events. Usually, engineers use an isolator as a high voltage level shifter for extending the common mode range thereby reducing the ground noise. The LTM2893 is intelligent enough to ignore transients events of the common mode type up to 50K V/μs, as this provides a low-capacitance isolation barrier along with fully differential data communication.

When dedicated SPI isolators and other general-purpose digital isolators isolate ADCs, they use multiple digital isolators for supporting signals such as busy status or conversion start signals. In addition, they offer a 3- or 4-wire SPI port. They also suffer from signal propagation delays, as the isolated SPI port must wait for the return of the acknowledgement signal before the next data latching can occur. Adding all the propagation and the response delays from the ADC SPI port, a single read may suffer a delay of about 35 ns. Therefore, although the initially rating of a digital isolator may be at 150 Mbps, in reality, the delays reduce the effective frequency to 25 MHz or even less.

Linear Technology has provided the LTM2893 with a dedicated master SPI engine on its isolated side, and a dedicated slave engine and a buffer on the logic side. The master SPI engine of the LTM2893 monitors the status signals from the ADC, fetching the data as soon as its BUSY signal goes low. There is no interaction with the logic side once the conversion has started.

The buffer register on the slave SPI engine on the logic side receives data from the isolated side via the isolated barrier. The two sides therefore, operate independently of each other.

What are Linear Actuators?

Any device creating motion in a straight line is a linear actuator. A vehicle is an excellent example of linear motion—the engine makes the car move forward or back in a straight line, unless the driver changes the direction. Other examples of this application are available in the process industries, material handling, food, and beverages processing industry, robotics, and many more.

The industry uses different types of linear actuators powered by pneumatics, hydraulic, and/or electric. As it is natural for pneumatic and hydraulic power to produce linear motion, they are simple devices and the industry often calls them cylinders. On the other hand, electric powered linear actuators almost always use a rotary electric motor. That means converting the rotary motion to a linear one through a belt or a screw/nut system. Although conversion does make the electric linear actuator somewhat more complex than pneumatic or hydraulic actuators are, using electricity can offer significant advantages in several applications.

Engineers must make a crucial decision when selecting the type of linear actuator they prefer for use in a specific application. For instance, although the pneumatic cylinder offers the advantages of lower cost and ease of use, the user often confronts potential compressed air leaks that reduce the efficiencies in operation. Similarly, although providing high-thrust capabilities, a hydraulic cylinder is prone to fluid leaks and they may not be very friendly to the environment.

On the other hand, electric linear actuators offer distinct benefits:

  • Ability to handle complex motion profiles
  • Ability to adapt quickly to changing needs
  • High efficiency, lower energy usage, and lower lifetime costs
  • Integrates easily into other electric production systems

With motion-control systems becoming increasingly more complicated, electric linear actuators provide precise control of force, deceleration, acceleration, and speed. Their ease of use allows them to outperform easily other technologies dependent on fluid power. Easily handling complex motion profiles, electric linear actuators offer infinite positioning capabilities with data feedback and high accuracy and repeatability.

It is easy to change the programming of an electric actuator. As parameters change, changing the program allows the actuator to adjust to the new specifications. Not only does this minimize downtime, it also reduces loss of productivity in the industry.

Compared to the 10-15% total system efficiency for pneumatic systems and 40-50% for hydraulic systems, electric powered linear actuators operate at 70-80%. Although the initial acquisition cost may be high, electricity powered linear actuators offer savings over their lower total life cycle cost, apart from the savings in energy use, efficiency, and reduced maintenance.

If all other equipment in the system operate on electricity, it is easy for users to integrate electric actuators also into the motion control system. Users can take advantage of integrating electric actuators in systems that use PLCs, HMIs and other similar devices for enhancing motion control, data collection, and diagnostics.

In the market, numerous actuator types/styles are available and they come in various degrees of precision and cost. For instance, one can have models that offer high repeatability, but with moderate accuracy. It is necessary to understand the requirements in the application for selecting a suitable actuator.

The Importance of Decibels in Electronics

Engineers use decibels everywhere for calculating power levels, voltage levels, reflection coefficients, noise figures, field strengths, and more. Most instruments use it, whether they are signal generators, spectrum analyzers, test receivers, power meters, network analyzers, or audio analyzers. Despite this, decibels remain a mystery to most people, sometimes including experienced engineers.

Engineers deal with numbers in all their professional activities, with some numbers being very large or very small. However, most of the time, rather than the numbers themselves, it is the ratio of two quantities that is more important. For instance, the base station of a mobile radio system many be transmitting 80 W of power, of which only 2×10-8 W or 2.5×10-8 percent reaches a mobile phone.

For dealing with very large or very small numerical figures, it becomes easier to use the logarithm of the numbers instead. For instance, the above base station transmits at +49 dBm, while the signal strength reaching the mobile phone is at -57 dBm. This makes the level difference between the two 106 dBm.

The main advantage in expressing ratios in decibels is they become far easier to manipulate. Adding and subtracting decibel values needs a much lower mental effort than to multiply or divide linear values.

Although a ratio cannot have dimensions, engineers use units of Bel to honor the inventor of the telephone, Alexander Graham Bell. The use of decibel makes the numbers more manageable, with decibel being one tenth of the Bel. Just as we multiply meters with 1000 to convert them to millimeters, we need to multiply Bel values by 10 to convert them to decibels. Therefore, dB represents ten times the ratio of two power values expressed as a logarithm to the base 10.

Since the decibel is a ratio, engineers must express arbitrary power levels with reference to a fixed quantity, as this allows proper comparison of the power levels. Telecommunication and radio frequency engineers most commonly use the reference quantity as the power of 1 mW into a 50-Ohm load. That is how in our example above, expressing 80 W of power in dBm becomes 10 x log (80/0.001) = 49 dBm. Although earlier, some engineers used the natural logarithm with a base of e, nowadays, engineers use the base 10 logarithm almost exclusively for calculating dBm.

Although the concept of decibels involves the ratio between two power levels, this can be easily converted to a ratio between two voltage levels, since the knowledge of power and resistance helps in finding the voltage across the resistance.

Apart from dBm, engineers use other reference quantities such as 1 W, 1 V, 1 µV, 1 A or 1 µA as well. In these cases, they express the dB quantities as dBW, dBV, dBµV, dBA, and dBµA. Similarly, for field strength measurements, these become dBW/m2, dBV/m, dBA/m and dBµA/m.

Engineers obtain absolute values when expressing power level ratios using the reference values above. Therefore, they call these absolute values as levels. For instance, a level of 10 dBm represents a value 10 dB above 1 mW, while a level of -20 dBµV represents a value 20 dB below 1 µV.

ATtiny Remote Power Switch for the Raspberry Pi

One of the shortcomings of most highly popular single board computers such as the Raspberry Pi (RBPi) is the lack of an on/off power switch. The board springs to life as soon as you insert the micro USB power cable into its socket. If you simply switch off power or pull out the micro USB cable off the RBPi, you stand the risk of not only losing data but also of corrupting the file system. Therefore, to shutdown the RBPi safely, you need to call a shutdown command, which closes down the file system and takes the RBPi into a safe state, allowing you to remove the USB cable.

The above has been the reason for several projects to incorporate a switch with the RBPi that will safely switch it off without corrupting the file system. Most of the projects incorporate a board sitting on the GPIO header of the RBPi along with a micro USB connector and a toggle switch to control the power supply for the RBPi. The entire control of the power supply comes from a tiny microcontroller on the add-on board, which monitors the state of the toggle switch and the RBPi. In turn, the microcontroller switches a MOSFET and an LED indicates the status of power. This also precludes the necessity of unplugging the RBPi from the power module after switch off.

This power switch from Nanomesher, using an Attiny85 microcontroller, adds a new dimension to controlling the RBPi—it has a remote that you can use to remotely control power to the RBPi. The entire arrangement comes as a kit, and you get a hack able and smart power switch for the RBPi that a removable Attiny85 microcontroller controls. There are also four jumper cables that allow the board to connect to the RBPi GPIO, a high quality micro USB cable 20 cm long, and an infrared remote control.

The project is hack able in the sense you can remove the ATtiny85 microcontroller and reprogram it to provide any type of functionality with the remote. Of course, reprogramming the ATtiny85 will require an Arduino-compatible platform such as the Uno. Other Arduino devices with switches are available, and you may already own some, or you may buy them for experimentation. The ATtiny requires wiring up with the Arduino on a breadboard for the programming.

You can use the included remote or any other remote already available with you. Since the kit is hack able and reprogrammable, you can make it recognize many more signals, changing the timings and functioning of the shutdown. For instance, you may add another button for a hard reset, and reprogram the Attiny85 to recognize it.

Although the kit does a fine job of shutting down the RBPi safely, the presence of the jumper wires to connect to the RBPi makes the kit somewhat cumbersome to use. The project would have been much more useful if the kit could be fitted onto the RBPi in the form of a HAT. Of course, the presence of jumpers does make the kit more flexible since one can select the GPIO pins for connection.

Low-Side & Hi-Side Current Sensing

Electronic systems tend to manage their power consumption to reduce the production of heat as waste. This calls for optimizing the system efficiency by effectively distributing power. As the voltage applied to the circuit is usually a constant, engineers monitor power consumption by keeping track of the current drawn by the circuit—power being the mathematical product of the current and voltage fed to the circuit. Current sensing has additional advantages, mainly that of maintaining the health of the system, preventing circuit faults from turning disastrous, and preventing batteries from over-discharging.

Engineers use two basic methods to monitor electric current. The first method follows Ampere’s law, and engineers measure the magnetic field surrounding a current-carrying conductor. The second method follows Ohm’s law, and engineers measure the voltage drop across a small resistor inserted in series with the circuit. The first is a non-intrusive method, but useful only for regularly changing currents, such as alternating current. It is also an expensive method, rather prone to temperature coefficient errors and effects of non-linearity. The second method is simpler, but introduces an element of insertion loss.

The semiconductor industry offers resistive-sensing techniques that are cost-effective and accurate, while making measurements suitable for various applications running on direct current. The resistive-sensing technique relies on sensing the current on the low-side or on the high-side of the circuit, the optimal approach depending on the application.

In resistive sensing, engineers insert a low-value resistor in series with the current path. This produces a small voltage drop in proportion to the current the circuit is consuming and which passes through the resistor. An electronic sense amplifies this tiny voltage to make it easier to process further. However, the sense resistor’s placement depends on the environment of the application and this can present some serious challenges for the sense amplifier.

If the position of the sense resistor is between the load and the circuit ground, a single operational amplifier, acting as a sense amplifier, is adequate to amplify the resulting voltage drop. Engineers call this low-side sensing, and is different from high-side sensing, where they place the resistor between the positive lead of the supply and the load.

In both cases, the sense resistor must be of adequately low value to prevent it from dissipating high power, but its value must be high enough for it to generate a detectable voltage for the sense amplifier to multiply it accurately. The sense amplifier multiplies the difference of voltage across the sense resistor, but uses a common-mode voltage for the purpose.

For low-side sensing, the common-mode voltage is close to the ground, and the rest of the circuitry following the sense amplifier may run on low voltage. However, high-side sensing requires the common voltage to be close to the supply voltage, and sometimes this may be high enough to present supply voltage problems for the circuit following the sense amplifier.

Some applications are unable to tolerate the tiny voltage drop introduced by the sense resistor on the low-side. The situation aggravates as the load current increases. For them, engineers have to follow high-side sensing inevitably.

What are Ball Grid Arrays?

Initially, surface mount devices, especially ICs, came as perimeter-only packages, with pins for soldering placed along the edge of the device. As ICs became more complex, they needed more pins for external interfacing, which made the packages larger. Manufacturers soon realized there was a large unused real estate that lay just under the package. Therefore, they made the ball grid array (BGA) packaging, which, in place of pins, had solder balls aligned in a grid under the device. Soldering BGAs involves melting these solder balls onto pads on the PCB.

Using BGAs leaves a considerably larger area free on the PCB. Compared to mounting a package with pins on its perimeter, BGAs offer better thermal and electrical properties, and this has made the format popular, following the continued miniaturization of electronics.

Since their introduction, although their basic concept has remained the same, BGAs have changed in dimension and now come with far smaller pitches and smaller outlines. There are varieties as well, with some packages having connections only on the periphery and none at the center, while others have the connections distributed evenly across the bottom of the package.

For simpler BGAs, routing traces on the PCB is simple as the balls are placed well apart or there is space in the middle of the device. However, with increasing pin counts and decreasing pitches, routing between the pins becomes more difficult, resulting in increasing the layers of the board, thereby increasing the cost and reliability concerns.

As BGAs become increasingly more complex, designers have to depend on vias to connect the BGA with the rest of the circuitry on the PCB. Vias are small holes drilled through the multilayer PCB and plated with copper to provide connection between pads and traces on different layers. Some vias are through-hole types, meaning they start and end on the two extreme layers of the PCB, and may connect to other layers in between. Other vias can be blind types, starting from one of the outermost layers and ending on an internal layer, possibly connecting other layers in between. Blind vias are not visible on the PCB surface as they start and end at different internal layers, and may connect other internal layers as well. However, all the above require great precision while manufacturing, and are expensive processes.

Ordinarily, PCB designers prefer not to use vias on a pad, as during soldering, vias can wick solder from the pads leaving the joint in a dry and unsoldered state. However, with BGA pitches getting increasingly smaller, designers do not have much choice, but tenting is offering a way out. Tenting allows filling the via hole with an insulating material and covering the top with a layer of copper, thereby preventing wicking.

As the BGA pins lie in between the device body and the PCB, traditional soldering methods such as hand soldering and wave soldering are no longer useful, and assemblers rely on infrared heating or reflow ovens to solder BGAs to a PCB. This requires a pick-and-place machine placing the BGA package precisely on the pads and uniformly heating the area to form the actual connections.

How Do Power Supplies Share Current?

Those who use power supplies to run different devices often face a peculiar problem. The load may demand more power from a single power supply that it can safely provide continuously. Since the voltage to the load has to remain constant, the situation calls for using additional power supplies to supply the excess current, and inevitably, users must connect them in parallel. However, simply connecting power supplies in parallel does not guarantee they will share the load current between them in an acceptable manner to operate normally.

Although designers do design some power supplies with dedicated circuits within them to ensure proper sharing of load current when connected in parallel, this is not a generalized practice. Moreover, even if power supplies of one manufacturer can optimally share current when connected in parallel, they may not do so when operating in parallel with power supplies from another manufacturer. In fact, power supplies from the same manufacturer but different models may also not work satisfactorily in parallel.

Theoretically, an ideal voltage source will supply unlimited amounts of power all the while maintaining a constant voltage level. Real power supplies have a limit to the amount of current they can supply to the load. If a load wants to draw power beyond the capacity of the supply, it will reduce its output voltage such that the power delivered remains within its capacity. Should the demand for current increase further, the output voltage reduces further until it reaches zero, and the power supply shuts down. Recovering automatically or through an external reset from an over-current situation is a design feature.

In reality, all voltage sources come with a positive and non-zero internal impedance. This drops the output voltage at the terminals as the load current increases. Power supply specifications call this change in output voltage with load current as the load regulation, and this is specific to each power supply. As the requirement is to have the output voltage change as little as possible with increasing current, some power supply designers prefer to design for low output impedances. Some power supplies have remote voltage sensing to boost the output voltage by the amount it has drooped. However, this is not desirable when sharing current.

One of the problems in connecting power supplies in parallel to supply higher current than either can supply is the current balance characteristics of the units may not match. In case the error in the initial voltage settings between the units is bigger than the depression in the output voltage at maximum load, the first unit may supply its entire share before shutting down. This leads to the second unit attempting to deliver the load current, and since it cannot do so, it shuts down as well.

One of the methods to enable proper current sharing is to enhance the output impedance of each unit so that their individual output voltage droops at full load is far more than the no-load voltage difference between the units. Although the voltage regulation of the system degrades significantly due to the intentional voltage droop, the current sharing between the power supplies is more successful.

ElectroSmash Pedal for the Raspberry Pi

Guitarists favor expensive gear. For instance, they hold online discussions about the best types of wire for guitar pickups. They even go to great lengths while selecting the type of transistors that will give them the best fuzz tone. They hold extensive discussions about the merits of the pentode rectifier over the tetrode type. While the geeks in the electronics world share several common characteristics with the guitar geeks, the ElectroSmash Pedal Pi would interest both.

Both teams are already familiar with the single board computer, the Raspberry Pi (RBPi). ElectroSmash provides a pedal that works with the RBPi Zero and allows the user to program the effects. The brains behind the project are in the code that the user has to download and compile on the RBPi.

Although it is possible to write the code afresh, but downloading the sample provided by ElectroSmash is more sensible, and gets you started faster. The community behind the Pedal Pi has contributed the code, and the user has the complete freedom to use it as it is, or to modify the parameters. ElectroSmash provides the Pedal Pi in a kit form, which means owners have to assemble it first.

Instructions for the assembly are available from the ElectroSmash website. The kit comes with all components neatly labeled, which makes the kit easy and straightforward to put together. One does not need extensive soldering experience for the assembly.

The kit has two ICs, the first an op-amp, and the other an analog to digital converter chip. Follow the instructions on the ElectroSmash site to place them on the board the right way around.

Typically, the RBPi Zero comes with the header pins not soldered to the board, and the user has to do the placement and soldering. However, one can get around this problem by using the RBPi ZWH variant, as this board comes with the header pins soldered in place.

Once you have assembled the pedal, you may find it is not as robust as the regular guitar pedals available on the market. According to ElectroSmash, the aim of the Pedal Pi project is to offer learning about guitar pedals and having fun with them. As an electronics kit, the ElectroSmash Pedal Pi kit certainly lives up to its claim.

Although the kit may seem slightly expensive, comparing it with other guitar pedals shows its true value. For instance, the distortion pedal from Ibanez, the classic Tube Screamer, costs almost twice the full kit. Although the ElectroSmash kit has about ten other effects built in, the user can add many more—in fact, only the programmer’s ingenuity, imagination, and programming skills limit the range of effects that the kit can handle.

Following the code sample that ElectroSmash provides is simplicity itself. They list the code sample in order of increasing complexity, ranging from the simple tone to the looping effect. The user can have fun playing with different types of distortion and use a processed quality on the fuzz, bit-crusher effect, and distortion. The effects are all available in the file fuzz.c and one can change a few numbers to give a new effect.

Connecting Wireless Temperature Controllers

Modern industrial temperature controllers are not just simple thermostats, as their earlier counterparts were. With the ability to control upwards of a hundred parameters, the latest industrial temperature controllers allow users to set not only temperature points, but also program alarm settings based on adjustable ramp parameters. Users can select the RTD or thermocouple they want to use for collecting data, while setting limits on the set points.

With the advent of digital temperature controllers, users can configure them with a physical interface. Although, initially, the design of some models allowed them to connect to nearby computers through a wired link, the later models of temperature controllers come with Bluetooth enabled.

Traditionally, the physical interface of temperature controllers featured two to five buttons that allowed the user to set the various parameters for the controller. With the limited three to four character LED display on the controller, the user had to either know the button combinations or refer to a manual during the process of setting up the parameters.

Connecting earlier temperature controllers to PCs through wired serial interfaces presented other problems. It required the PC to be near the controller, as the interface and cable could cover only limited distances. This meant the PC had to operate in the noise and dust of the industrial environment, reducing its operational life. Cables connecting the two were prone to electromagnetic interference, and a tripping hazard. Most modern PCs come with only USB connections, and do not have serial interfaces any more, complicating the situation further.

Bluetooth enabled industrial temperature controllers have solved the above problems with ease. Several controller can connect to one mobile device with an app using Bluetooth—a short-range connecting technology. As the user brings the mobile device within range of the controller, he or she can ping the controller to confirm the specific device to interact. The app on the mobile allows the user to interact with the controller for viewing and setting all its parameters and for reviewing any of its error messages.

With the app interface offering greater graphical flexibility, the user can read the error messages and parameter names in plain text. Moreover, he or she can access in-line help for further understanding the function of each parameter and its permissible settings.

The graphical app interface allows the user to set up the temperature controller easily. It does not require the user to page through a manual or memorize the settings. No cables or other inconvenient interfaces are necessary for using these modern mobile interfaces.

With the unprecedented growth of cloud-enabled devices and the Internet of Things, there are concerns about information security in wireless connectivity. Using Bluetooth technology in industrial interconnections has its own advantages. Bluetooth is currently unable to connect to LAN, industrial Ethernet, or to cloud services, and is therefore, secure to that extent.

Furthermore, Bluetooth technology functions over short distances, and communications are limited to within 70 feet, limiting long-range interference. Moreover, users can protect controllers with passwords. Users can select the parameters on the controller that the password will protect, and a remote user cannot change them through the app.

Do You Need EMC Testing?

Any electronic product faces a necessary hurdle before it goes to the market. It must clear the Electromagnetic Compatibility (EMC) test. This being a critical test in the design journey of an electronic product and passing this crucial test proves the design is right.

However, most designers relegate this important emissions testing to a late part of the design lifecycle of the product. This unnecessarily increases the risk of cost overruns and project delays shortly before the planned launch. Therefore, it is necessary to test for emissions at various stages of the product design plan.

When testing for EMC, you are actually minimizing the possibility of the radiated or conducted emissions from your device interfering with other electronic products nearby. Simultaneously, EMC testing ensures that the product under design is impervious to electromagnetic emissions coming from other sources in the vicinity.

Electromagnetic emissions are the energy the product emits in the radio frequency (RF) range. The device may emit these energies in either conducted or radiated form.

Below about 30 MHz, conductors and cables are not very efficient as antennas. At these frequencies, they are rather good at conducting the RF energy through shared loads and power sources. The conducted emissions, when passing through them may start interfering with other electronic equipment.

As the frequency goes up, beyond 30 MHz, conducted emissions are no longer an issue. At these high frequencies, cables and conductors start behaving more as antennas radiating the energy, thereby causing interference with other equipment.

Engineers use different test procedures and equipment for measuring conducted and radiated emissions. Although they use almost similar filter components for mitigating their effects, the electrical values involved are different.

Standards for measurement and testing electromagnetic emissions for both the conducted and radiated type differ in the US and Europe. While the US uses FCC Part 15, Europe uses CISPR 22/EN 55022. However, both approaches are very similar, and if the equipment meets the requirements of one of the standards, you can rest assured that it will meet the needs of the other standard as well.

Both the US and European standards set separate specifications for conducted and radiated emissions. The two types of emissions have their own limits applicable to the final system and its power supply.

Manufacturers making internal mountable power supplies often test them to meet regulations as standalone products. However, this is not enough if your design is using one of these power supplies with a load. In such a case, it is necessary that the complete system meet the EMC regulations. As a metal box encases the power supply, meeting the EMC challenges requires using external components.

Additionally, as most power supplies use switching topologies, they produce high levels of radiated and conducted emissions. Although the manufacturers may have already mitigated these emissions during the design phase, adding load to the power supply may produce further emissions. Therefore, it is necessary to test the combined system to ensure it meets the requirements of the EMC standards. Usually, a certified lab using calibrated test kits does the final testing. However, certain in-house testing is also possible, not requiring much equipment.