Numato Labs - One stop for FPGA Development boards/Expansion modules

We have been searching for a platform where we could buy reliable FPGA development boards and finally one day we saw a board in www.numatolabs.com. Without second thought we ordered one board which is suitable for us. We received the board today and till now the response from Numato was exceptional.

Advantages of using boards from Numato:

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2. Good technical information regarding the board in the site

3. Chance to raise queries using help@numato.com 

4. Quick and flawless delivery

5. Good follow-up

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Circuit Debugging - Tip 1

Let us start learning some of the debugging techniques. Very common component used in electronics is DIODE. Sometimes, by mistake we tend to connect diode in reverse. So, before, mounting a diode the first thing we have to check is the ANODE and CATHODE. The below symbol indicates the polarities and corresponding representation.

If you still have doubt on the polarity, you can check using multimeter. The below figures shows the same:

Why use Aluminium for mechanicals?

Have you come across mechanical designs for your projects, then definitely you know that aluminium is the most preferred material for such. There are various reasons  for using aluminium and have a glance at the list below:

• Good thermal conductor
• Good electrical conductor
• Can be shaped easily as per requirement
• Weighs less, density (mass per volume) is less
• Durable, soft
• Resist corrosion
• Non-magnetic
• Aluminium is the most abundant metal of all.
• Gets less affected by environment factors like air and water
• Doesn't effect the environment, can be recycled
• Less chances of ignition

The conductivity of Aluminium is 50% of copper but still used widely because of cost factor compared to copper.

Very familiar Applications:

• Have you seen light poles in your area, they are made of aluminium
• Electrical grid lines
• Your kitchen cooking utensils
• Heat sinks for electronic components and mother boards
• Bus/car/Rail/Aircraft bodies are made of aluminium
• Railway tracks
• Cool drink tins

Note: Aluminium may not be used directly in any application and it is compounds (aluminium + other metals) that are used.

Understanding RS232 interface/signalling - Part 1

Serial port commonly to as RS232 communication is the most widely used interface in embedded systems. Whether it be micro-controller, processor, FPGA the basic interface and the slowest interface that is used is serial port. RS232 communication complies to requirements of EIA/TIA-232 and V.24/V.28 standards. the two main terminologies we come across in these standards are DTE and DCE.

DTE is nothing but an equipment which transmits or receives digital data. This equipment processes the data and converts it into relevant form the users. One of the best examples of DTE is Personal computer (PC). The other examples include printers, fax machines, etc.

DCE is nothing but a simple level converter kind of circuit to make the DTE compatible with communication equipment. Sometimes DCE is a part of DTE and doesn't exist independently. Modems existing in the market are an example of DCE.

The following figure shows the connectivity between DTE and DCE in it's simplest form.

Note: RS232 full form --> Recommended standard-232

Using crystals in embedded applications - Part 5

What is series resonance and parallel resonance in crystals?

Series resonance crystal does not have any reactive components like capacitor. Parallel resonance crystal is used where there are reactive components involved. Series resonance crystals are resistive in nature where as parallel resonant crystals combine the phase shift properties of reactive components to determine the oscillator frequency. The following circuits explain the difference.

Parallel Resonant circuit

Series Resonant circuit 

In a parallel resonant circuit, load capacitance is a critical specification.Load capacitance is the capacitance which is seen across the terminals of crystal. When we use this crystal in the application, this load capacitance must match the load capacitance requirements of the device to which crystal is connected. 

A same crystal can act as series as well as parallel resonant. When used in an application, the first resonance at which crystal oscillates is the series resonance and later when reactive component like capacitor is added it oscillates at different frequency which is called parallel resonance. So, from this point if i want to use a parallel resonant crystal and we use a series resonant crystal my crystal operates at a higher frequency than desired. In turn, if a parallel resonant crystal is used in place of series resonant requirement, the parallel resonant crystal operates at a lower frequency than specified.

What is the bandwidth of crystal?

The difference between series resonant frequency and parallel resonant frequency is called the bandwidth of the crystal. Lower the bandwidth higher the stability of the crystal. As per the quality factor definition, (Centre Frequency/bandwidth), lower the bandwidth higher the quality of the crystal. So, for your application choose a crystal by checking at the quality factor curve.

What is the crystal equivalent circuit?

In the above circuit,

Co = Holder capacitance (capacitance contributed by leads extending outside the crystal)

L1 = Motional inductance

C1 = Motional Capacitance

R1 = Series resistance

The common term used in crystal specification is hermetically sealed package. What does that mean?

Hermetically sealed meant air tight enclosure with only provision for external connectivity. In our crystals case, the electrodes are extended out.

What is the difference between AT cut and AT strip crystals?

AT cut is the cylindrical version of the crystal and AT cut is the stripped version of cylindrical crystals for miniature crystals.

What constraints can affect the crystal performance?

• Assume that we connected a crystal in our application, the drive provided to the crystal should not exceed the specifications of crystal. If drive provided exceeds the rating, the crystal life time gets reduced.
• Temperature at which the crystal is operated
• Improper load capacitance can vary the crystal frequency from the desired value

What are the fundamental and overtone specification of a crystal?

Fundamental frequency is specified for lower frequency crystals (around 8 MHz, 24 MHz, etc) where as overtone is odd multiple of fundamental frequency. Overtone crystals are not preferred for micro-controller applications.

Using crystals in embedded applications - Part 4

Ceramic resonator (vs) Quartz Crystal (vs) RC Oscillator (vs) Silicon Oscillator:

• Ceramic resonator and quartz crystal are mechanical resonant devices where as oscillator works on electrical phase shift principle (where R-C are the phase shift circuit).
• Power consumption of Ceramic is more than quartz crystal. 
• Ceramic resonators have good rise time than quartz crystals.
• Ceramic resonator and quartz crystal operate on the same principle as the electrical signal applied to them causes mechanical vibrations. 
• Ceramic resonators are more rugged than crystal.
• Quartz crystals are very stable and maintain their frequency under extreme conditions. Quartz crystal may not drift from it's frequency even when the PCB stray capacitance is high. Also, at quick varying temperatures, the quartz crystal remains stable.
• Ceramic resonators are made of ceramic material which are not as stable as quartz. These are piezoelectric in nature.
• Comparatively, Quartz costs more than ceramic resonators. 
• Ceramic requires much higher load capacitance required to quartz crystal.
• An oscillator is addition of feedback to the crystal along with amplification such that oscillations happen. Take the case of micro-controller, on the external clock pins we add a crystal and combined with internal circuitry it forms a oscillator.
• Oscillator is immune to EMI and humid conditions as they come packaged with all components for frequency generation.
• Temperature co-efficient which is a important material property is low for crystals and resonators.
• Ceramic resonators are available in miniature packages also.
• Ceramic resonator can sometimes be of compound material which helps change the characteristics of the crystal as per the material.
• The main disadvantages of oscillators is package size and cost and sensitive to vibration,  

Note: Some micro-controllers have internal capacitors, in this case, there is no need to have external capacitors.

Considering the disadvantages of ceramic resonator compared to Quartz, where do they find application?

Check the age old radio circuits you find resonators. Also, they are used in cost critical application and applications where stability is not important criteria.

What is the main selection criteria for any clock input?

Accuracy is the important criteria. Depending on the application for which the circuit is used, clock must be chosen properly. For example, applications like USB, SATA, PCIe requires a very stable clock with less deviation from the desired frequency.

Note: There are R-C oscillators internal to some ics which have very less stability but is a very cheap implementation. Micro-controller internal RC oscillator is an example.

Using Wi-Fi modules - Part 1

Using wireless technology for connecting to external world is the trend. Gone are the days where people used those Ethernet cables which didn't allow people to move around while browsing and other activities. Now it is very common that you see more tablets, smartphones, mini PCs and even desktops connected using wireless technologies. PCs use wired Ethernet and Wi-Fi for connectivity whereas smartphones rely on Wi-Fi and GPRS connectivity. So, Wi-Fi is one of the common mode of connectivity whether it be any media. So, when you are planning to use Wi-Fi module in your application it is always important you make a right choice of the module you are using.

To those starters, you have to know that a Wi-Fi is enabled in your device using a transceiver chip which has an antenna connected to it. The antenna acts as a transducer and helps in communicating to external world.

What need to be looked at when you are choosing a W-Fi module?

• Encryption type in the module
• WEP, WPA, WPA2 types
• Wi-Fi standard
• IEEE802.11a/b/g/n
• Supports point-to-point or access point connectivity
• Cost perspective
• Range
• In-built antenna present or not
• TLS (Transport layer security) support
• Form Factor
• Can have a web server or not? (HTTPS support)
• Interfacing to controller (UART/SPI/SDIO)
• Operating temperature
• Physical contact of the Wi-Fi module with the mother board
• Certifications
• Power consumption
• Customer support of the vendor
• Module dimensions

Basics: Why Active low signals used?

Are you working on digital circuits? Then you must be using control signals in your design and must be hearing about terminologies like ACTIVE LOW, ACTIVE HIGH. We sometimes just follow the design recommendations and never think of the need to do it. Let us analyse the need for Active Low in our designs.

What is active low?

A general criteria while using any control signals (like Enable) is to make it HIGH from LOW state. But in some cases, like the chip select and reset it is in reverse, the signal will be initially HIGH and when it is turned LOW, it means that particular signal is asserted (when asserted, it changes the connected chip functionality as desired, can say connected chip changes state). Control signals which are used in this manner are termed Active Low. The terminology itself tells that signal is termed active when it is LOW.

How is Active LOW signal differentiated from Active HIGH signal?

The representation of the signal (as per the Active HIGH or Active LOW ) in the datasheet of that particular chip is different. Active LOW is represented by having a dash on top of the signal name. Chip Select if active low is represented as (CS).

Reasons for using Active LOW only:

• Let us assume that you want to choose a device between n-channel MOSFET and p-channel MOSFET for your application. One would always prefer going for n-channel as electrons are the majority carriers in this type of device and have the highest mobility then holes. In this case, when the transistor is ON, the output is driven low. So, a normal condition is that output is high and when transistor in on output is low. This is one of the factor which makes implementation of active low state easy. Same mobility case applies to BJT also where NPN is preferred compared to PNP.
• Active LOW always helps eliminate indeterminate states due to improper supply voltages. 
• A genuine reason is that it is easier to pull down a signal than pulling it up. 
• Under a Active low condition, it is always easy to use wired-or condition and apply common reset to several chips. So, fanout can be increased. Control signal count can be reduced.
• For critical signals like Reset, it is always important that a state is maintained properly, if they are made active high, any noisy transitions may cause improper reset in the circuit. So, a state of high initially and then making it low to reset the chip can be the best option. 
• Consider the sourcing capability for example of a micro controller which doesn't go beyond 10 mA. If you want to source more you may have to use an external driver. In these cases, it is always preferable that we use Active LOW. For digital circuits, sink current capability is more than source current.

Wireless Charging - The emerging trend

Many of us use a wall mount charger for charging out multimedia devices like smartphones, tablets, music devices, etc. These devices have a socket into which the external charger goes in. It is always recommended that you use a suggested charger for a specific device. What if you don't have to use this wired charger and charge your mobile hassle free? Yes, this is what wireless charging is. Just place your mobile on a charging pad and your mobile gets charged, as simple as that.

Wireless charging is based on the principle of magnetic induction. Magnetic induction meant there will be two coils in which the first coil (transmitter) has a current flowing through it which causes magnetic flux. when the second coil (receiver) is placed near to first coil the magnetic flux induces current in the second coil. So, a charging pad on which you place the mobile will have a coil in which flux will be developed. When you place your mobile right next to the charging pad, which has a second coil , it induces current and hence battery charges. Basically, it is the electromagnetic field that plays a role here.

An alternative to magnetic induction is resonant charging. In this the receiver need not be next to the transmitter. Both of them work on the principle of resonance. In this way of charging power is transmitted wireless at a 6.78 MHz rate. In this case, the resonance helps charging.

What are the various wireless charging standards?

• A4WP (Alliance for wireless power)
• PMA (Power Matter Allaince)
• WPC (Wireless power consortium)

WPC developed Qi standard which is the most popular now and is in use. Qi is basically the magnetic induction type of charging. Regulatory approvals are in place for this standard.

A4WP developed resonant type charging. Regulatory approvals not in place.

What are the challenges from the designer point of view?

Let us take a smartphone designer, who wants to implement wireless charging in his device. The challenge for him is to select a chipset which is used as receiver. The chip has to support the desired standard. Also, the charging control circuitry to be implemented to connect to unit to be charged (battery). Chip sets are also available in the market which supports various charging standards. Coupling factor is of primary importance. A higher coupling factor leads to faster charging rate.

What are the various vendors for wireless charging chips?

• IDT
• Broadcom
• NXP
• Texas Instruments
• Freescale
• STMicroelectronics

What are the various domains wireless charging is expected to get exposed to?

• Smartphone charging where the charge pads can be mounted outdoors at public places like bus stops, cafeterias.
• Electric vehicles charging (Battery)

What are the differences between Inductive charging and resonant charging?

• For inductive charging, the receiver must be in the close proximity of transmitter (receiver and transmitter separated by centimeter distance) where as for resonant charging this is not the case.
• Coupling factor is high in inductive charging
• Size of the coils is more in inductive charging than resonant charging
• Cost is also high for inductive charging than resonant charging
• Efficiency is high in inductive charging
• Heat is more in inductive charging

Soldering Techniques

We might have heard about soldering techniques used by manufacturers to place/solder components on a bare PCB. For an experienced guy, these techniques are familiar but for a fresher these all look like hard stuff which add to the additional burden of learning. The two most terminologies you hear from manufacturing industry are wave soldering and re-flow soldering. If PCB is not so complex and if you are getting your PCB s soldered at your local manufacturing locations you may not be hearing more about re-flow soldering. Let us look at the major differences between these two techniques.

Wave soldering:

Wave soldering is used to solder both through hole and SMD also. But this technique may not be suitable for most of the SMD components. Even in this era of surface mount technology, there are many applications which demand through hole components. So, wave soldering is a popularly used technique.

Reflow soldering:

Reflow soldering is mainly used for surface mount components. Even the through hole component soldering can be done with this technology. In this soldering technique, a solder paste is added to the PCB to glue the components upon which is the PCB is exposed to a controlled temperature environment. Check the datasheets before selecting the component and check your manufacturing facilities in parallel to give a manufacturing guideline for maximum reflow temperature to be used. Reflow machines can be of infrared type or conventional type.

What are the latest technologies?

Now-a-days embedded market is growing faster enabling the technology to be used at every step. SMT reflow machines are having lots of inventions incorporated and are coming up with latest technologies. some of the important observations are:

• Graphical view of the temperature using a display attached 
• Touch based screens for control activities
• Minute temperature adjustment 
• Complete process level data logging
• Advanced cooling strategies
• Efficient flux distribution techniques
• Tracking the PCB from insertion to completion
• Power consumption reduction in latest machines
• Alarms for security
• Remote control

What are the advantages of latest innovations?

• Less maintenance costs
• Exceptional thermal performance
• Labour reduction
• Automation
• Quick turnout and hence high throughput
• Controlled environment
• Less chance of failures
• Report generation at every step

Understanding Oscilloscope Specifications - Part 2

Oscilloscopes can be said like heart of electronics testing especially protocol and high speed signals testing. Now a days oscilloscopes come with integrated test benches which help analyze high speed signals like USB, SATA, etc. These inbuilt test benches analyze signal specifications to the minute level and give a complete test report as a package. As a tester, this adds lot of flexibility and helps built confidence on the design. For a tester using oscilloscope initial challenge lies in understanding  specifications of it and selecting a right one for his application. 

Types of oscilloscopes:

The modern oscilloscopes come in various form factors which can be as big as bench-top to as well as wearable type and  middle level as hand-held type/pocket type. Hand held, pocket and wearable types are a very good addition to the field application engineers. That heavy packing, fright charges for a field engineer are no more a burden. The only disadvantage with these portable scopes is that their bandwidth is very less. So, the extent of debugging that can be done by the field engineer with these scopes is very limited. Even with such limitation, it is worth having one with you. Some people always have an eye on the pricing and cost wise they are nothing to worry as most of them are available in the range of $100 to $300. There are oscilloscopes especially designed for debugging phones during development.

Range of bandwidths:

Based on the domain you work on the oscilloscope varies. If you are working on a very low end digital signals and buses like SPI, I2C, SMBUS and UART, you don't need a very high end oscilloscope. The bandwidth requirement for such applications is very less and a 100 MHz bandwidth scope like TDS2014C works very much in such cases. If you are working on high end RF to high end digital signal signals, high bandwidth scopes are a necessity and be careful in choosing bandwidth of scope based on highest frequency to be measured. If you want to measure a frequency of 2.5 GHz, you must have a scope of bandwidth of at least 7.5 GHz. Today oscilloscopes are available up to 100 GHz. 

Waveform Generation:

One of the feature of oscilloscope is you have a output port which outputs fixed frequency signal. Hence, an oscilloscope can also be used in case you need a reference frequency for testing.  

Power dissipation calculation for Linear and Switching regulators

For any hardware designer, power consumption control is a big challenge. Lower the power consumption of your product higher the success rate. For a battery operated devices like mobile, tablet and other smart devices power consumption is a critical specification. One critical component in this power consumption/wastage across the board is regulator. Power from the main source like battery, usb power is distributed across the board using regulators. Regulators can either step-up or step-down the input a DC voltage. Based on our requirement we choose a regulator type.

Regulators used in embedded hardware boards can be mainly classified as linear and switching regulators. There are several sub classifications in linear and switching regulators which we will discuss later. For now let us calculate the power dissipation calculation across Linear and switching regulator. For this we will take an example of devices from Linear technologies.

Linear Regulator: LT3014B

Switching Regulator: LTM8020

Power Dissipation calculation for LT3014B

I/P voltage range: 3V-80V

O/P voltage range - 1.22V-60V
Dropout voltage - 350mV

For a linear regulator, as the output current from the regulator increases, drop out voltage increases which is shown in the graph below from datasheet of LT3014B

Let us assume i want a output voltage of 5V @20mA from LT3014B. To achieve this output, minimum input required is 5.35V. Let us assume, we are providing a input of 7.4V which is Li-ion standard battery pack voltage.

The power dissipated across the linear regulator is (7.4-5)*20m = 48mW

If the input is 50V and output is 5V, then power dissipated is (50-5)*20m = 0.9W

So, we can clearly see that as the difference between input and output is increasing in a linear regulator, power dissipation across regulator is going high. Also, imagine a case where input to output voltage difference is low but current is in amperes, in this case also, power dissipation across linear regulator is very high.

Important note: If the input to output voltage difference is high, or if the current output from regulator is high, power dissipation across linear regulator is very high in which case heat dissipation is high. We may need a huge heat sinks if we use linear regulators in such cases. Also, power is unnecessarily wasted.so, we have to go to switching regulator in these cases.

Power Dissipation calculation for LTM8020

I/P voltage range: 4-36V

O/P voltage range - 1.25-5V

The main factor to consider in switching regulators is efficiency. For a given load current, the efficiency can be calculated from the graph below as from LTM8020 datasheet.

To calculate power dissipation across switching regulator LTM8020, we have to take above graph into consideration. Let us assume my load is drawing 100mA for a input of 24V at output of 5V. In this case, from the graph efficiency is ~82%.

For above requirements, output power = 5v *100mA = 0.5W
Input required power = output/effeceincy = 0.5/0.82 = ~0.6W

So, power dissipated across LTM8020 is, 0.6-0,.5 = 0.1W

Important note: If either the input to output voltage difference is high, or if the current output from regulator is high, power dissipation across switching regulator is less in which case heat dissipation is less. We may not need a huge heat sinks if we use switching regulators in such cases. Also, power is not unnecessarily wasted.So, we have to go to switching regulator in these cases.

Diodes - Part 1 (Button diode, Cell diode, Pressfit diode)

Engineers outside automotive domain might never have thought how a automotive battery gets charged. A hardware engineer in automotive is very much familiar of those technical details. The whole mechanism happens with the help of alternators which convert mechanical energy to electrical energy. The electrical energy generated at this point is alternating one. So, either to charge the battery or to provide the power to the ECU (Engine control unit). So, rectification has to happen. The process of rectification converts alternating current to direct current. For these purpose we use rectifier diodes.

Button diode, Cell diode and Press fit diode are types of rectifier diodes used in rectification process. These are especially designed for automotive applications.

Advantages of rectifier diodes (Button type, Press fit, Cell diode) used in automotive applications:

• Low leakage
• High reverse voltage rating
• Low cost
• High surge current handling capability
• High operating temperature
• Plastic Casing on these diodes meet flammability standards

Thermal paste/compound - A small note

Thermal paste is a heat sink compound used on top of the processors (whether it be graphical or central processor), regulators for heat to follow smoothly to external medium. The mechanical designers suggest using a heat sink based on the thermal calculations. The principal behind using a heat sink in that the operating temperature of the device should not exceed the maximum specified ratings in the datasheet.

Operating temperature of a specific heat generating device is calculated by summation of junction temeparature and heat generated (Heat generated is the product of thermal resistance and power of operation). When this sum exceeds operating temperature specification that effect is catstrophic and can lead to device failure.

So, we have to use heat sink on top to enable the heat to escape from the device. Keep in mind that thermal paste is filling the imprefections of heat sink. The heat sink will be mounted on top of the device. Even though the heat sink is placed on top of device touching it there will be a air gap in between. Air is always a poor conductor of heat in which case another media must enable smooth heat flow. For this purpose we use a thermal paste. Thermal paste is a highly heat conductive paste.You mave have a large heat sink with exception fin structure for smooth heat flow, but, without a thermal paste the entire cost you have put on heat sink is a mere waste.

The thermal paste applied on top can be of different types. These can be electrically conductive as well as non-conductive. In a electronic board, it is always prefferable to use a non-conductive type. Cermaic based paste is one type of thermal paste. Arctic silver is the most preffered thermal paste.

What is Integrated Heat Spreader?

Keep in mind that the modern processors have a metal kind of enclosure for heat flow assistance. This we call a integrated heat spreader (IHS).

I already have a heat sink compound on the device. How do i clean it?

Usin Isopropyl Alcohol. Use a isopropyl dipped smooth cloth to rub off the paste.

Conformal coating for PCB

Engineers who worked on hadware boards which have to operate very low temperatures might not have come across conformal coating requirement. But who work on marine, defence, military, aerospace domains and hardware board designers who worked on board designs which have to work up to high temperatures and humidity might have used conformal coating. Now a days we can see conformal coating being used very extensively across other domains also (Telecomm, industrial, automotive, instrumentation). We can say that where there is a need for reliability and high protection conformal coating of PCB is a must.

Conformal coating is a chemical coating on top of the assmebled PCB which helps electronics to get shielded against harsh environments. If you have seen some relays, transformers available in the market, they have a plastic enclosure for internal electronics with a gel compound filled for protection against shock, vibration, stress, thermal, corrosion, moisture. This is what we call "plotting". You can see the huge black ics in the below figure.

Plotting is an expensive technique and conformal coating helps to achieve the protection simpler. The also disadvantage is that specific temperatures are used to form the protective layer which may cause the electronics to loose bonding. Conformal coating also adds dielectric strength to the PCB. Also, conformal coating ensures board reliability. Conformal coating can protect electroincs boards against the following problems:

• Temperature (which we call thermal cycling in environmental tests)
• Humidity
• Moisture
• Mechanical stress
• Dust accumulation
• Fungus formation
• Corrosion because of salt spray
• Shock & Vibration
• Chemical contamination

There are specifications available forconformal coating guidelines especially in military and aerospace. For example, MIL-1-46058 is one such sytndard. Silicone is the most commonly used conformal coating material used for protection against high temperatures.

What are the various other conformal coating materials available?

Silicone, Epoxy, Acrylic, Urethane, Parylene. Urethane is the most widely used.

Once conformal coated, can we remove it?

Yes, it can be removed and there are several techniques available. Approach the manufacturer to get to know the type of material used and technique to remove coating. Acrylics are the easiest to remove.

What care need to be taken for resoldering a component on already conformally ciated PCB?

Once conformally coated, very high temperature must be applied by soldering machine to remove that coating. This may cause SMT pads to get lifted. In susch cases, careful attention must be provided while aplying temperature beyond certain range. Also, once rework is done take care that conformal coating residue is not present on the board which can give a problem in the long term. Take care of ESD which performing such procedures for removing conformal coating.

What can be the thickness of conformal coating?

Have seen a conformal coating of thickness up to 50um.

What are the advantages of conformal coating?

• Eliminates need for costly mechanical enclosures
• Less weight
• Easy removal

What are the techniques used for conformal coating?

• Brush
• Spray
• Dip
• Automated

What care need to be taken for conformal coating?

Eliminate any surace defects. This means you have to equally spray without any gaps

Chose the conforming material as per the application and requirement

Choose the conformal coating technique as per expertise available

The drying process after coating must be simple. Can be air dired, normal dried or UV dried.
Coating material complies to industrial standards and is environmental friendly

How can suraface defects be detected in conformal coating?

Using UV light inspection

Film capacitors in various applications - A note

The following are the advantages of film capacitors that make them suitable for various applications:

• No polarity
• Reliable
• Stability
• Available from pF to uF
• High surge current capability
• Low inductance
• Low cost
• Low ESR
• High precision capacitor value
• Can withstand high power 
• Value retention for longer time, long life
• High voltage withstanding capability
• High frequency handling capability
• Customization

What is a film capacitor?

A film capacitor uses a thin layer of plastic as dielectric. Later, this is treated to come up with various film capacitor types like metallic film capacitor, polyester film capacitor, PTFE film capacitor, etc.

Various applications:

There are several advantages of metal film capacitors that make them useful in various applications. Have you seen the latest LED bulb applications? The most preferred capacitor is metal film type. These are relatively stable and cheaper which makes them suitable for low margin and stability desired LED market.

We can see PTFE film capacitors (polytetraflouroethylene) used in aerospace and military applications. PTFE film capacitors are heat resistant, so, this is preferred.

Snubber circuits use polypropylene film capacitors. This is because of their higher current carrying capability and low inductance.

Other applications:

• Filters
• Lighting ballasts
• decoupling capacitors
• RFI suppression

What are the disadvantages of film capacitors?

• Bulky compared to other capacitors
• Difficult to find SMT parts for these capacitors for all values
• Little costly

Lightning connector - Apple accessory

To put it straight forward, this is a type of customized connector used in Apple products. Like how we have USB micro AB type connector on all smartphones and tablets, apple products have their customized connector on their phones. Previous versions of iPad/iPhone used to have 30-pin connector which is replaced by 8-pin lightning connector.

The lightning connector and the old 30-pin connector (docking) are shown in the figures. the 30-pin connector carries power as well as signals and can be used for docking purposes. The 8-pin lightning connector can be inserted either side. 30-pin connector was used in Apple products till the 4th generation. The 30-pin docking connector carries Audio, USB, Fire wire and other control signals. 

Later versions started extending video over the connector dropping Fire Wire. The 5th generation of iPhone started using lightning connector. To use a 8-pin lightning connector with 30-pin docking connector, you must have a adapter.

Advantages of lightning connector:

1. Light and small compared to 30-pin connector

2. Lightning connector has a control chip on it which takes care of the direction even though connector is assigned in reverse.

3. Connectivity to various output types is easy by using adapters.

 4. Within a small pin out various outputs like audio, video and controls can be connected.

The pin out of 8-pin lightning connector is shown in the figure shown above.

5. Any signal in the pin out can be used for power which is very flexible.

6. Edge detection mechanism is used to detect a plug connected to the 8-pin connector.

Displays - Pixels - Part 1

Displays are part of everyday life. Be it our mobile screen, Television screen, PC screen, display forms a most important human interface. From the age old CRT displays to the latest OLED type displays, the display technology has been evolving day by day. Did we ever think of curved displays to be designed? Let us discuss about different display technologies and terminologies in series of articles.

Pixels on the screen:

Be it any display, the display arrangement is in the form of pixels. A single pixel is also called “Picture element”. The pixels are arranged in the x and y direction. The pixel information will be taken care by the operating system of the processor to which display is connected which helps to form an image on the screen.

1-bit/B&W displays:

1-bit displays are used to represent Black & White displays. Based on the bit value of 0 or 1, Black or white value is represented. 

8-bit/256-color displays:

8-bits of information are dedicated for each pixel which can vary up to 255 combinations. So, a 8-bit color displays can have up to 256 colors. These are used in color displays which came immediately after black and white displays.

24-bit/True color displays:

24-bits are used to represent each pixel on the screen. Each pixel uses 8-bit for R, G, B to form a color. This gives complete color information compared to 8-bit displays and are called true displays. Each pixel can represent up to 16M (16777215 in particular) colors.

RGB combinations:

The pixel color information will be a RGB model where the respective color of the pixel can be formed by the percentage of combination of RGB. Full percentage of RGB (255,255,255) represents a white where as the null combination of RGB (0,0,0) forms black.

Digital Living Network Alliance (DLNA)

Assume you have a mobile, TV, PC and multimedia devices at home and you would like to play a video taken from your camera over TV. Previously, you would have transferred the contents to DVD drive using PC, then play that DVD using some multimedia device. But think of a technology where you can play the videos from you camera directly connecting to TV. Yes, this possible using DLNA (Digital Living Network Alliance). DLNA helps various multimedia devices in the home to communicate between each other. DLNA was started by Sony.

Multimedia devices like TV, DVD/Blu-ray players, smart phones, tablets, PCs and other commercial devices can be part of this network. For this you only need a wireless/wired connection and a application installed on these multimedia devices.  The only requirement is both the devices must be DLNA compliant. DLNA defines standards like any other protocols.

In DLNA also, the same Client-Server architecture applies. If you want to transfer data from your PC, install softwares like Twonkyto make it a server. Also, TVersity is another example.  On the receiver side you have Smartshare, Allshare.

Except Apple all other smart phone vendors like Intel, HP, Motorola, HTC, Microsoft, Samsung, LG and Panasonic are making products that will happily communicate with each other. Apple uses AirPlay. This is just not a feature of android phones, NOKIA is bringing it to windows phones also.

You can detect a DLNA device by seeing a DLNA logo on the product you have purchased.

FPGA vs ASIC

FPGA - Field Programmable Gate Array

ASIC - Application specific Integrated circuit

FPGA is seen in many applications these days and many of us are aware of it. But we often here about ASIC which is confusing. ASIC is designed to be used for specific application where as FPGA is generic. Designers tend to use FPGA for initial development of their code and then order for ASIC for their final design. FPGA consumes less time in design cycle as the only challenge lies in selecting a suitable FPGA and then write your code. ASIC consumes more time to come to market as it has through cycles of making, floor planning, routing, timing analysis, verification and manufacturing. Let us study more differences between ASIC and FPGA from the below table.

DDR3 vs DDR4

The rate at which the memory technology (in terms of speed) is always higher compared to the counter parts around. Now that the DDR4 is sampled out, let us see differences between DDR4 and it's predecessor DDR3.

We will discuss in detail the implementation and technical details of DDR4 in future articles.

Using crystals in embedded applications - Part 3

In the previous articles, we have discussed about external components used around crystal for stable output frequency signal generation. We also, discussed about the load capacitance and how to match this load capacitance with the external reactance components. The input-output capacitance, output resistance determine the reactive components outside. Here are some few more points to be considered in this aspect:

• The internal CMOS inverter gate inside the processors/controllers and other main integrated circuits are generally operated in active region. The gate must be designed such that it must overcome loss in the external feedback resistor and frequency decisive components (Damping resistor, external load capacitance).
• As the CMOS inverter gate is operated as a linear amplifier, the characteristics like phase and propagation delay also to be considered.
• Just to throw a small a small light on CMOS inverter, it is a combination of P-MOSFET and N-Mosfet.

• The above circuit is nothing but a unbuffered inverter circuit.

Parameters to consider for crystal oscillator selection:

• Operating frequency
• Supply voltage (decides logic level)
• Operating temperature
• Storage temperature
• Tolerance/Stability
• Rise/Fall time
• Load drive capability (in terms of capacitance, pF)
• Desired output logic type
• RMS Jitter
• Start up time

Retina display

Retina display patented by Apple is a LCD display used in its products. The products include iphone, ipad versions. The main difference from other displays is the pixel density and resolution. Pixel density represented as Pixels per inch (PPI) differs from other displays available in the market. The pixel density has been adjusted for various display sizes so that user will have a smooth viewing experience. Retina displays are tented to be the best in the market and other displays like Super AMO led, IPS display, OLED, LCD lag retina display by some distance.

Retina display debuted with iphone 4s. The pixel count PPI exceeded 300 in this display. With such high PPI and resolution, user will never be able to differentiate individual pixels in a display and image looks reality with such a high resolution. These high resolutions of up to 2560x1600 gives user a printing read experience.

What are the advantages of Retina display?

• Good color reproduction
• Wide viewing angles
• High contrast displays (great color differentiation)
• Reduced glare
• High quality displays
• Ambient light sensor helping in brightness adjustment, improves power saving sometimes
• Back lit LCD improving brightness
• IPS technology improving wide angle views

Local interconnect network (LIN)

Local Interconnect network (LIN) is a 1-wire interface used in automobiles mainly intended for diagnostics implementation. LIN is a serial interface used as a replacement for costly and feature rich CAN interface. LIN is a robust communication protocol which supports automotive environments. LIN basically can be said like a inter-chip communication. The slaves can be daisy chained or connected in shunt.

LIN supports master-slave configuration as like other serial protocols and protocol can address up to 16 slaves. LIN is mainly an automotive protocol also intended for usage in industrial applications. Check any microcontroller supporting automotive applications, you will find LIN interface.

LIN supports a hierarchical node structure where data is transferred between nodes in a fixed format. The master sends the synch data and identification fields to which corresponding slave responds.

To connect microcontroller to network using LIN, a LIN transceiver is required. This is in similar lines to uart communication. For internal communication within an automotive application, LIN interface is preferred.  At the broader level, CAN is used for communication.

Specifications of LIN:

• ·         Single master, 16 slaves
• ·         No bus arbitration as like I2C
• ·         Speed up to 19.2kbps
• ·         Maximum bus  length supported is 40m
• ·         Half-duplex communication
• ·         2-byte, 4-byte, 8-byte frames
• ·         Error detection mechanism

What are advantages of LIN?

• ·         Simple interface
• ·         Low cost and efficient in implementation

Understanding Oscilloscope specifications - Part 1

A very important test and measurement equipment in the hands of electronics engineer is Oscilloscope. An oscilloscope gives a real time visual inspection of the signals on board. In other words, it captures and graphically represents an electrical signal on display. Choosing an oscilloscope for a specific application is always challenging. There are several versions of oscilloscopes in market and to name some of them are analog oscilloscope, Digital storage oscilloscope, hand held oscilloscope, PC based oscilloscope, etc.

You may not be able to use oscilloscope in every case. For example, let us assume you want to measure a RF signal of frequency 20GHz. Then oscilloscope doesn’t fit your need. You might need a spectrum analyzer for your measurements. Spectrum analyzer does measurements in frequency domain (Amplitude vs. Frequency) where you get a frequency spectrum of the signals. Oscilloscope does measurements in time domain (Amplitude vs. Time). The main reason for oscilloscopes not having that range for measurements is the sampling rate. For 20GHz, sampling rate must be too high which can’t be achieved with scope.

The main criteria on which we select an oscilloscope are:

• Analog bandwidth
• Sample rate
• Memory depth
• Resolution
• Triggering capability
• Channel count
• Cost
• Reliability
• Accuracy

Analog bandwidth: Analog bandwidth applies to all types of scopes. Every scope has a front-end amplifier and maximum frequency that can be passed through this amplifier determines the scope band-width. I other words, analog bandwidth determines the maximum signal frequency that can be measured with a given scope. For example, if a scope says a bandwidth of 50MHz, signals up to 50MHz can be measured. So, as you go higher in frequencies to measure signals like USB, PCIe, SATA, etc, you need more bandwidth.

Generally, if the measured frequency is of ‘x’, scope bandwidth preferred is 5 times the frequency to be measured. This is for correct reproduction of the signal. So, one might have a question regarding the maximum frequency a scope can measure. This maximum bandwidth is of the same terminology we use in filters, a 3-db bandwidth. The maximum bandwidth is the point at which the signal input diminishes by 3-dB. So, a signal is shown diminished in voltage if it goes beyond this frequency.

As Analog bandwidth rating increases, the scope gets costly. So, while choosing an oscilloscope, study your requirements and come up with a optimal decision.

The main challenge of the scope designers is to maintain perfect signal characteristics (undershoot, overshoot, ringing) as it passes through various input stages of the scope. In other words, maintaining signal fidelity is very important.

Sample Rate: One of the important criteria for DSO is sample rate. In accordance to Nyquist rate, for good reproduction of the signal, the sampling must be greater than twice the signal frequency. But for good reproduction, in scopes you need minimum of 10 samples for good reproduction of the signal. Sampling in a scope can be in Mega samples per Second (MS/s) or Giga samples per second (GS/s). The more the sampling rate, good the measurement.

Let us assume we are measuring a 20MHz signal with an oscilloscope of 1GS/s sampling rate. Then, the scope samples the given input signal at 50 times in a given cycle.

Memory Depth: The samples captured are stored in an internal buffer before signal reproduction. The amount of memory is indicated by a factor called memory depth. Memory depth is an important specification which affects the performance of oscilloscope. Memory depth and sample rate are inter related. Let us assume you have a scope with good sampling rate but with less memory depth, then you may not be able to utilize the maximum sampling rate of the scope. So, while purchasing a scope, checking the memory depth is as important as checking the sampling rate.

Let us assume a scope with 5K buffer size (memory depth) and 1GS/s sampling rate measuring a signal of 50us. Then the scope can sample at 5K/50us = 100MS/s which is well below capability of scope sampling.

Triggering capability: The triggering capability mainly determines the oscilloscopes capability to measure one shot signals. In a real time scenario let us assume a signal expected to be of max. 1V amplitude is having some distortion at a specific point causing the signal to go above 1V. In such scenario, the point at which it goes above 1V can be captured using triggering functionality. 

What are the advantages of Digital storage oscilloscopes (DSO) when compared to age-old analog oscilloscopes?

• Storage facility
• Remote connectivity (Ethernet)
• High band-width
• Smaller in size
• Display measurements on screen
• Single shot as well as repeated signals can be measured

How to select a scope if I am measuring signals in milli volts and micro volts range and signals of high voltage level?

To measure low voltage ranges consistently, the scope must have high resolution ADC. Generally, ADC will be in the range 12 to 16-bit for a given scope. If signal to be measured are of high voltage, use attenuating scope probes. When measuring high voltages, use 10:1 attenuation factor. This helps scope protect against accidental high voltages. Also, 10:1 probe setting minimizes the overload condition.

How to determine a matching probe for a given oscilloscope?

You cannot use every possible probe with a given scope. The scope vendor generally gives the matching probe specifications for a given scope model. The probe capacitance mainly determines the usage. The probes used should match with the band-width of the scope.

How to select the oscilloscope in terms of rise time requirements?

The oscilloscope rise time must be one-fifth of the fastest rise time of the signal to be measured. If this is not met, a distorted waveform appears on scope which in real time may be perfect.

What probes need to be chosen for measuring high frequency signals?

The capacitance of the probe determines the frequency at which probe can be used. As the measured frequency increases, the normal passive probes may not be suitable. For measurement of high frequency signals, it is preferable to use active probes. Active probes have a FET amplifier inside. These active probe have a good matching capability.

Who are the vendors of oscilloscopes in the market?

• Agilent technologies
• Tektronix
• Lecroy
• Fluke
• Gwinstek
• Oscium
• Hameg
• BKPrecision
• Promax
• EZ Digital

Power consumption - A issue to deal with in hand held units

Compared to embedded designs few years back, the stress on power savings has been more these days. May it be the increase in hand held products or whatever your circuit consuming lowest power is a very important feature. And this power saving is very critical in battery driven applications. As we know, most of these hand held devices are driven by batteries. With the Li-ion battery becoming prominent because of it's advantages over Ni-Cd battery it is being used in the hand held units. So, for any designer of a handheld unit first he has to justify his battery usage. More the power consumption lesser the battery life and also it is the other way. 

To a no-voice in embedded designs, the power consumption may be confusing. Consider a battery which has a rating of 1000mAh, this rating means that  a battery can supply an amount of 1A continuously over an hour. So, if your circuit draws for example 1A, then your battery lasts for only 1 hour. In designs, let us assume if you can vary your circuit current consumption, as per the need of the hour then there is always a chance that you give your battery more life before next recharge.

So, stressing the battery as per the need always helps battery to last long. To understand more, let us take the example of your mobile, you have a setting in your mobile to power off the back light after some specified amount of idle time. The lesser you make the idle time before the back light goes off the more it is helpful to increase battery backup. This is very high level from a user point of few. But from the designer end, he has to take to care of many things in his design before an end user can start getting the benefits like the ones we mentioned above.

Let us take a design into consideration, where we have a processor and it's associate circuitry on the board which are powered by battery. The below list indicates the opportunities a designer has to reduce power consumption.

• Use different states of processor efficiently: Sleep, idle, standby, normal, run
• The more you keep the processor in idle state the more you save power. You can observe some of your gadgets sudden having a back light enabled when you press a key or because of some other action. What happens in this case is that your processor will be in idle state with only some peripherals working. So, when you press a key, the processor gets an interrupt and comes to normal mode.
• Try to optimize system clocks and processor clocks. Clocks are one of the major contributors in the circuit in terms of power consumption and using them efficiently can help you in reducing power consumption.
• We see these days inter ic communications being operated at a low signalling levels which helps reduce power (Ex: LVDS)
• Reduce the capacitance on your board as much as possible
• Take care that your circuit doesn't draw excessive power during start ups.
• Isolate the logic from processor and use other circuitry which consume low power (Like implementing digital logic in low power device like CPLD)
• Wherever possible implement your logic in interrupt mode rather than polling.
• Understand the glue logic requirement on your board and implement it in a efficient way.

Braking resistors

Most of us must be familiar with the normal resistors like the Chip type, MFR type, etc. There are some of these applications where we have to handle high power. In such cases you use power resistors. There are many applications in which we use a molded power resistors in high power applications. We have to remember that most of these resistors are metal clad and mainly aluminium housing. Aluminium is most preferred as it is economical and also environmental friendly. Some companies even make custom resistors, shape and value desired as per the end user application. 

There are some applications where the braking of the device generates electrical energy which can be absorbed at that instant or it flows back into the supply system. We call it regenerative braking or rheostat braking. Braking resistors are one kind which find application in motors. the main purpose of the braking resistors is to slow down the motor and drain out excess voltage. This helps the motor to be within safe tolerances. Under normal operating conditions of motor, it converts electrical to mechanical energy, but when motor is powered off, the magnetic field generates back emf which must be controlled for smooth power off of motor and keep it within safe tolerances. The braking resistor is used for the purpose. As we know, DC motors have permanent magnets which creates this electrical energy. In a AC motor, the generated magnetic field creates this effect.

Selection of braking resistor is a design challenge. The heat generated by the resistor on power dissipation is high and requires heat sink arrangement. this adds up to the cost. If the requirement is to stop the motor quickly, the resistor value must be less and dissipates more heat as it allows large current to flow through.

General ratings:

• Resistance (in ohms)
• Power dissipation (kW)
• Wire wound resistors