Archive for the ‘Electronics Design’ Category

Flex circuits

Tuesday, May 21st, 2013

Flexible printed circuits are useful when the size and shape of your invention is integral to its overall design. Very many consumer electronics gadgets have them inside: in mobile phones, cameras, etc. Tips for Building a Flex Circuit article tells that because of the unique characteristics that set them apart, an electronics engineer must consider additional factors when designing these circuits: the degree of bending, the tightness of the bend, how the bend will be formed, and how frequently the circuit bends. Tips for Building a Flex Circuit article tells the key factors to consider when building a flex circuit board.

Basics of Flex Circuit Design article tells that reliability, designers must create flex circuits that are neither too thick nor bend too much. The neutral-bend axis is a key concept in flexible-circuit design: tension or compression on the outer layers of the circuit depend on their distance from this neutral-bend axis and the radius of the bend. A circuit should flex no more than necessary to handle the goals of the design. In general, 90° is considered the maximum angle any circuit should bend. Avoid unnecessary thickness. Tight bends conductor traces boost the risk of circuit damage. Small conductors of less than 10 mils can tolerate compression better than stretching. If you use surface-mount (SMT) components, be aware of their special requirements. Avoid “discontinuities” in the bend area. Copper plating is less ductile than rolled, annealed copper, making it more susceptible to cracking when flexed.

Hackaday.com lists many flex circuit projects that could be worth to check out or DIY hardware hackers. They prove that flex circuits can be successfully build even on home laboratories.

How USB drives are made

Sunday, April 28th, 2013

Hackaday article Hand placing flash die to make USB drives tells how boards inside USB drives populated. The article points to Where USB Memory Sticks are Born article that tells that once the bare die FLASH chips are screened for functionality, they are placed by hand onto a PCB (using some sort of tool made out of hand-cut bamboo). According to the article this is not an unusual practice for a value-oriented wirebonding facility.

Will the SMD resistors marking become a history?

Wednesday, April 17th, 2013

The markings on SMD components have been always hard to read. Besides the fact that the numbers and letters in them are very small, the number coding used on them is different than what is used on traditional though-hole components (the reason is that there would not be enough space to print any long codes to those components). How to decipher those SMD resistor codes has been always a hard task. Pages like SMD Resistor Coding, The SMD Codebook, Marking SMD have tried to give some help on this.

Hackaday.com reports that it might be soon time that you can forget how to decipher those SMD resistor codes. Looks like surface mount resistors might be unmarked like their capacitor brethren. There are several reports (electronics-lab.com, dangerousprototypes.com and soselectronic.com) titled Will the SMD resistors marking become a history? that basically tell the same story: Company YAGEO announced its intention to remove marking of RC/AC 0603,0805,1206 SMD chip resistors from July, 1-st, 2013. The reason for this step is to reduce unnecessary chemical usages for environmental protections.

On EEVblog Electronics Community Forum there was discussion on will the rest of the manufacturers take the same decision. The clearest comment was: Sadly I’m sure they will. It’s not like any of their big customers are really going to care, and if they can eliminate an entire step of the production process the bean counters will ejaculate.

smd_soldering

Everything seem to imply, that the situation with marking of chip resistors (0603/0805/1206) will soon be similar to chip capacitors (i.e. no marking on the top of the component, just component reels have the marking). A lot of SMD resistors already don’t have markings. But that should not be shocking news. You can put probes on your SMD component to verify there value is correct with your multimeter. It was not much of a problem with caps it wont be a real problem with resistors.

10 Ways to Destroy an Arduino

Sunday, April 14th, 2013

10 Ways to Destroy an Arduino article tells how you can accidentally destroy Arduino board. Use a sledgehammer, fire a bullet at it, throw it into a pool….that’s not what we’re talking about. We’re going to show you how to electrically destroy your Arduino:
Method #1: Shorting I/O Pins to Ground
Method #2: Shorting I/O Pins to Each Other
Method #3: Apply Overvoltage to I/O Pins
Method #4: Apply External Vin Power Backwards
Method #5: Apply >5V to the 5V Connector Pin
Method #6: Apply >3.3V to the 3.3V Connector Pin
Method #7: Short Vin to GND
Method #8: Apply 5V External Power with Vin Load
Method #9: Apply >13V to Reset Pin
Method #10: Exceed Total Microcontroller Current

When there are problems or potential problems, there are often commercial solutions to them. 10 Ways to Destroy an Arduino article was written by makers of The Ruggeduino board. Besides telling the problems, the article gives ideas how to solve most of those problems (interesting reading).

The Ruggeduino is a ruggedized Arduino-compatible microcontroller board. It’s features include overcurrent and overvoltage protection on all I/O pins and 5V/3.3V outputs, ESD protection on all I/O pins and USB port, total microcontroller overcurrent protection, and operation at up to 24V. I have written earlier on my blog on that board at http://www.epanorama.net/blog/2011/08/23/ruggeduino/.

Twisted pair RCA cables again

Saturday, April 6th, 2013

I wrote few years ago blog article Unshielded RCA cable is bad design. I just received yesterday a comment on it:
“It’s not always that simple. There are equipment combinations which REQUIRE twisted pair RCA. Here’s explanation: http://www.youtube.com/watch?v=QOagVDZLQnA

So I watched this Truth about RCA signal cables video mentioned on this comment:

The video was pretty well made and I can fully agree most of the things said on the video. Here are some information picked from the video.

Here we discuss the circumstances of when it is appropriate to use a twisted pair RCA cable vs a Coaxial RCA cable:
“Coaxial RCA cable is good and twisted pair is better”
“That’s not the case”
“There are specific cases where you would want to use each one of them”

You want to use coaxial if you have amplifier with single-ended inputs. In those inputs the outside of RCA is grounded. This type of inputs are used on average amplifiers (70-80% inputs in audio equipment). So for normal single ended RCA connections the coaxial cable is the right cable type.

The video says that if you have amplifier with differential input you want to use twisted pair wiring. Those are found on some of the high end amplifiers Only a small percentage of equipment have this type of RCA inputs.

If you mix those different cables and different input types, they don’t work that well: the connection become easily noisy.

According to the video if you have amplifier with differential input you would want to use twisted pair wiring. Those are found on some of the high end amplifiers Only a small percentage of equipment have this type of RCA inputs. I cam agree this. I have very rarely seen those differential input RCA connectors anywhere except some car audio equipment.

There is one considerable benefit on differential RCA input: The advantage is that there is no direct connection between the two grounds of the source and the amp, so no possibility for ground loops that, which could set up a voltage across the ground lead, which could lead to hum etc. There are no other advantages in sonic performance than the ground issue.

The video maker comments on Truth about RCA signal cables video page:

If the head unit has SE outputs and the amplifier has SE inputs = coax cable

If the head unit has SE outputs and the amplifier has Diff inputs = twisted pair

If the head unit has Diff outputs and the amplifier has Diff inputs = twister pair

If the head unit has Diff outputs and the amplifier has SE inputs = bad no matter what as you will shorting out half of the head unit’s outputs. In this case you would need an amplifier with Diff inputs or a converter to convert the head unit’s outputs to SE

According to those comments you need to what type of inputs and outputs your devices have to select the most suitable cable type. The differential inputs and and outs are like how XLR /balanced inputs work.

I said in my original Unshielded RCA cable is bad design article: When you wire unshielded twisted pair to unbalanced signal source and receiver RCA connectors, most of the good properties of the UTP cable noise rejection are lost. This holds true.

When you have system where you have unbalanced signal source and differential receiver, you get some of the benefits of differential system, but not all. The differential RCA receiver can get rid of the noise that is coupled as common mode noise to the twisted pair. In systems that use Balanced Line Technology the twisted pair cable construction combined with differential receivers and signal sources make sure that both inductively and capacitively coupled external noise to the wire pair gets converted to common mode noise that can be removed in differential receiver.

When you have system where your signal source is single-ended, things are somewhat different. Let’s consider first case where the single-ended signal source is grounded. In this case one of the signal wires is at ground potential and other carries the signal. The coupled magnetic fields generate the same amount of noise to both wires, so the magnetically coupled noise is still removed well differential receiver.

The story is different for capacitively coupled noise: There will be some capacitively coupled noise induced to the signal carrying wire (how much depends on electrical field strength and source impedance), but the same field does not cause any noticeable voltage on the grounded wire (it’s impedance is almost zero!). All this means that the capacitively coupled noise will not be coupled as common mode noise, and the differential receiver cannot get rid if it. Unshielded unbalanced cables are very sensitive to capacitive coupling especially when circuit impedance is high (impedance mostly determined by signal source output impedance in HIFI systems). The differential receiver does here nothing to help in this.

So I don’t think that unshielded twisted pair cable in this case would guarantee to be considerably better that coaxial cable. Depending on your noise source type, it could be somewhat better (only magnetic noise) or it could be considerably worse (against capacitively coupled noise on high impedance systems).

The situation for capacitively coupled noise is somewhat different if the signal source equipment is not grounded. In this case the impedance different the capacitively coupled signal sees is much smaller, so the signal gets coupled more equally to both twisted pair wires (not completely equally), and the differential receiver can get rid of most of the capacitively coupled noise to the cable. The downside with ungrounded mains powered equipment is that there is always some leakage from mains to equipment case, and this leakage can easily generate common mode noise to the cable that is much higher in amplitude than the audio signal on it (few volts to tens of volts depending on impedances and leakages). Usually at least some of that voltage gets to audio signal as noise because the differential inputs have their limitations on their common mode noise canceling capabilities (limited CMRR capabilies typically 40-70dB and sometimes the noise voltage can exceed the common mode voltage range the input can operate with). So if you are working with differential inputs you generally want the signal source to be grounded in way or another (or to be completely floating battery powered gadget or microphone).

The best cable for a setup that uses differential RCA inputs and single-ended output would be shielded twisted pair. The twisted pair construction would perform well against magnetic noise, and the shield (grounded at least on signal end) would get rid of the capacitive noise. So this would be the optimal cable.

A differential input only really works best with a balanced output and twisted pair/screened interconnect cable. This is how professional audio equipment that use Balanced Line Technology and XLR/phone connectors are typically wired. With this kind of balanced output and differential input system an unshielded twisted pair can also work acceptably.

The second best option for interconnection is unbalanced (single-ended) output wired to shielded twisted pair cable that is connected to differential input. Trying to use unshielded twisted pair here will give considerably worse performance.

So I can still stay on my original claim that Unshielded RCA cable is bad design. This will hold true very well. Exceptions to this rule (if there are any) are really rare. I can also say that twisted pair construction on RCA cables is better on some applications when the cable construction is shielded twisted pair.

In case the twisted pair cable used for interconnection is shielded twisted pair cable, I can agree on those comments on Truth about RCA signal cables video page:

If the head unit has SE outputs and the amplifier has SE inputs = coax cable

If the head unit has SE outputs and the amplifier has Diff inputs = twisted pair

If the head unit has Diff outputs and the amplifier has Diff inputs = twister pair

If the head unit has Diff outputs and the amplifier has SE inputs = bad no matter what as you will shorting out half of the head unit’s outputs. In this case you would need an amplifier with Diff inputs or a converter to convert the head unit’s outputs to SE

Feel free to comment if you disagree with my analysis and conclusions.

HackEDA

Wednesday, March 27th, 2013

HackEDA is an interesting looking new on-line electronics design tool. The premise is simple: most electronic projects are just electronic Lego: You connect your microcontroller to a sensor, add in a battery, throw in a few caps and resistors for good measure, and hopefully everything will work.

HackEDA takes all those basic building blocks and promises to create a custom Eagle schematic with all the parts your project needs. This looks like a good idea to develop more. Think of it as a mashup tool for electronics: the next time inspiration strikes, there’s that much less between you and the hardware you need to make it a reality.

Here is another somewhat related idea. Script lets you import Eagle boards for use in FreeCAD article tells an idea how an Eagle CAD circuit board design can be imported a proper CAD program in order to design enclosures.

For comparison another interesting idea to handle electronics as building blocks is implemented in Fritzing.

Wireless power for charging mobile devices

Tuesday, March 26th, 2013

Wireless power has become a hot topic as wireless charging of mobile devices is get getting some popularity. Wireless charging isn’t something new; the technology exists since 1981 and Nikola Tesla has made first wireless power experiments over 100 years ago. Wireless charging for Qi technology is becoming the industry standard on smartphones (pushed by Wireless Power Consortium) as Nokia, HTC and some other companies use that. There is a competing AW4P wireless charging standard pushed by Samsung ja Qualcomm. And there is more standards coming. Power Matters Alliance is heavily pushing their own wireless charging standard. It seems there is going to be fight on wireless charging in near future. It seems that right now we’re in the midst of a battle between two standards for wireless charging – Qi from the Wireless Power Consortium and Power 2.0 from the Power Matters Alliance. It seems that a common Wireless Power Standard Years Off as Battle Heats Up.

As obviously useful as wireless charging is, it suffers from a Tower of Babel problem with incompatible standards and competing interests keeping it from truly going mainstream. Wireless charging continues to be a niche category until there’s a common standard. Heavyweights are backing the idea of wireless charging capabilities embedded in phones, and public charging stations are beginning to pop up. Differing standards, however, still make for a rocky adoption. Realistically there probably isn’t room for two or more standards, which do essentially the same to end user but are incompatible, so expect some technologies to disappear in the near future. Charging portable devices without needing to carry a power adapter sounds handy when we can agree on one standard. “Wireless charging continues to be a niche category until there’s a common standard,” said Daniel Hays, a consultant with PricewaterhouseCoopers. “The hassle factor is still high.”

Qi seems to be at the moment standard that gets most attention. The news that Nokia to join Qi party with wireless-charging Lumia 920 have given lots of publicity to it. Even if the Lumia isn’t a big seller, the publicity and visibility it will provide for Qi should be enough to make everyone forget there was ever an alternative, if indeed there ever was. Also some HTC phones and Nexus 4 phone use this standard. Toyota launches the world’s first wireless charging of mobile phones in the car. Toyota’s car will get wireless mobile phone charger using Qi standard.

Qi has been here for some years. Qi has been around for a while, gaining the name and logo back in 2009. The Qi standard came out of water filtration units, which needed wireless power, and has been widely endorsed but devices are still quite rare. Under the Qi specification, “low power” for inductive transfer means a draw of 0 to 5 W, and that’s where mobile device charging solutions most probably go. The system used inductive coupling between two planar coils to transfer power from the power transmitter to the power receiver. The distance between the two coils is typically 5 mm, but can be expanded to 40mm.

The Qi system uses a digital control loop where the power receiver communicates with the power transmitter and requests more or less power via backscatter modulation. Besides low-power specification up to 5 watts, there is also a medium-power specification will deliver up to 120 watts. The frequency used for Qi chargers is located between about 110 and 205 kHz for the low power Qi chargers up to 5 watts and 80-300 kHz for the medium power Qi chargers.

Qi
Method: inductive coupling between two planar coils
Frequency: 110-205 kHz (80-300 KHz)
Communication: backscatter modulation

WiPower was a technology start-up company that used the principles of inductive coupling to develop a near-field wireless energy transfer system. Qualcomm bought WiPower in 2010 and started quietly negotiating with manufacturers to get the technology embedded in their kit. Qualcomm argues that the additional range of WiPower (which can charge devices up to 45mm away) allows new possibilities. WiPower system is based on modified coreless inductive technology and dynamically adjusts power supplied by the transmitter to power demanded by the receiver without the need for control systems or communication. WiPower chargers are claimed to operate at about 60-75 percent efficiency.

WiPower
Method: inductive coupling
Communication: no need for specific communication

Samsung and Qualcomm’s Alliance for Wireless Power (A4WP) promises more flexibility in wireless charging. Instead of induction, this standard will use loosely-coupled (LC) wireless power transfer (a series resonance-tuned pair of magnetically-coupled coils) to transmit power. This construction allows that the transmitter and receiver don’t have to be in direct contact, which gives more flexibility to industrial designers. This designs will support simultaneous charging of multiple devices with different power requirements. A4WP specification takes advantage of Bluetooth 4.0. The biggest downside in this design is that currently there are no products with this technology are yet on the market.

A4WP
Method: series resonance-tuned pair of magnetically-coupled coils (loosely coupled)
Frequency: 6.78 MHz
Communications: Bluetooth 4.0

The Power Matters Alliance (PMA) is working on an open standard for wireless charging. A group of companies back up this initiative (including Google, AT&T, ZTE, Starbucks, ,McDonalds, PowerKiss). PMA uses inductive charging method used in Duracell’s Powermat product. It requires the transmitter and receiver be close together, placing the mobile device on the charging pad.

This is quite new alliance but it seems to get lots of backers: over the last few months, the PMA has seen a tenfold increase in membership. One very big thing is that AT&T is seeking from its handset vendors a commitment to one standard of wireless charging.

The PMA is working to advance the widespread acceptance of the wireless power paradigm in multiple sectors. PMA is intent on leading and organizing the Power 2.0 agenda to commercial realization, while working under the umbrella of the most trusted name in standards: the IEEE. Powermat is capable of delivering 5-to-50 watts of power. Powermat allows a built-in check for alignment via light and voice signals based on RFiD Handshake feature. When you place a Powermat-enabled device on one of its mats, the two exchange a “handshake” using RFID: The mat identifies the device, determines how much power it needs and transfers energy to it. Powermat operates at 277-357 kHz frequency. Once a device is fully charged, Powermat stops the electricity from flowing. But as much momentum as the PMA has achieved, it is far from clear whether it will be that bandwagon.

Power Matters Alliance (PMA)
Method: inductive charging
Frequency: 277-357 kHz
Communication: RFID

As obviously useful as wireless charging is, it suffers from a Tower of Babel problem with incompatible standards and competing interests keeping it from truly going mainstream. There are also attempts to support several standards on one product. Samsung Galaxy SIII wireless power supports both Qualcomm’s WiPower and Wireless Power Consortium Qi. The Samsung Galaxy S4 will support both PMA and Qi standards. NXP has developed a charging station, which allows you to use both the general mobile phone charging standards (as well as one rare third standard).

The technologies I mentioned are not the only ones trying to push to the market in the near future. Apple is trying to patent wireless charging, claiming its magnetic resonance tech is new and that it can do it better than anyone else. Digitoday writes that Finnish research organization VTT is planning to combine wireless power and NFC technologies. The reasearchers believe that in the future NFC devices could be made to work as way to get power into device and send power to other device cheaply. Technology is not ready yet, because today’s NFC antenna circuits are not optimized for power transfer and there is no standard that covers this kind of use yet. NFC operates within the globally available and unlicensed radio frequency ISM band of 13.56 MHz.

Wireless Power: Convenient, But Its Shortcomings Are Somewhat Sour article tells that close-proximity inductive coupling is commonly estimated to deliver 50 to 70% efficiency. That’s considerably worse efficiency that what you get with a well designed wired charger. Intel increases consumer-product power consumption 50% blog post says that a system that is 50% efficient on top of the ac-dc conversion, and pumps RF energy all over the place is far from ideal in world where some other parties try to conserve every single watt. In a world with 15 billion chargers, energy efficiency is a big deal. Based in that is makes me a little bit hard to believe the Power Matter Alliance claims that wireless charging could save a lots of power in the future. How Wireless Charging Will Keep Toxic Waste Out of Landfills article tries to describe how wireless power could be more eco-friendly, but it is hard to believe all those claims without good data. I can believe that wireless chargers can have better energy efficiency than some old chargers supplied with consumer devices, but I given the limitations wireless charging it is very hard to believe that wireless charger could ever be more efficient than well designed wired charger. But wireless charger could be well “good enough” to be acceptable.

Who owns our modern stuff?

Thursday, March 21st, 2013

In my posting War on DIY Electronics I already told that that the trend is that electronics is heading to be less and less hackable. Wired has an opinion article Forget the Cellphone Fight — We Should Be Allowed to Unlock Everything We Own that has many good points that I can agree on. USA Congress is working on legislation to re-legalize cellphone unlocking. The copyright laws that made unlocking illegal in the first place and it makes many other things you might like to do illegal in USA.

Who owns our stuff? The answer used to be obvious. Now, with electronics integrated into just about everything we buy, the answer has changed, because in digital age even the physical goods we buy are complex (usually run by complex software that runs on embedded computer or many of them). Copyright is impacting more people than ever before because the line between hardware and software, physical and digital has blurred. We really don’t own our stuff fully anymore – the manufacturers do own at least some some important parts of it.

Because modifying and repairing modern objects (home electronics, cars, etc..) requires access to information (manuals, error codes, and diagnostic tools) that manufacturers don’t like to give out. Property rights issue is turning many regular people into criminals: When they try to do something manufacturer don’t like, the manufacturers claim those people are illegally “reproducing copyrighted material.” Fixing our cars, tractors, and cellphones should have nothing to do with copyright. We should be allowed to unlock everything we own.

Manufacturers have systematically used copyright in this manner over the past 20 years to limit our access to information to create information monopolies at our expense and for their profit. Most manufacturers seem to like to have a closed platform, walled garden or closed ecosystem.

Fortunately there are nowadays some exceptions to this rule, for example open-source hardware companies and open-source software companies. Open doesn’t conflict with money although it often appears to.

I do not think open conflicts with making money and further I think there are ways to make more money by being open rather than closed. Think about for example Internet, PC, Linux and Android. Open source software has created many well working businesses. Economic growth occurs whenever people take resources and rearrange them in ways that are more valuable.

Information on iPhone prototype

Saturday, March 16th, 2013

What did the iPhone look like before it looked like an iPhone? Apple’s popular product looked radically different in the early stages of development (like many other high tech gadgets). Image of the Day: iPhone prototype from 2005 article gives you view of the early iPhone prototypes. Check out the article for interesting photos.

That article is based on information from Exclusive: super-early iPhone prototype had 5″x7″ screen, serial port article, so it is a good idea to check that out. The early prototype was quite large—about 5″×7″ and roughly two inches thick. Interesting that this early prototype has a number of ports that Apple never intended to make it into the final product: USB ports, an Ethernet port, and even a serial port.

It is quite common to have this kind of ports in development prototypes, because ports like Ethernet and serial simply to make working on the device easier.

Touch screens and charger noise

Tuesday, March 12th, 2013

Why does not my tablet touch screen work when powered with third party mains power supply, but works with the original power supply? This happened to me. The power supplied I had were both for tablets (different tablets) and had similar basic characteristics (same current and voltage ratings).

The reason why the other power supply caused the touch screen to fail was related to the noise given out by the power supplies and the touch screen electronics sensitivity to this noise. One power supply outputs more noise than the other. How this noise affect the touch screen electronics is shown in this picture MoU regarding Harmonisation of a Charging Capability for Mobile Phones, June 5th, 2009.

This is nothing new, just now well documented what happens. This same happens with practically any today’s mobile phone charged based on switch mode power supply technology. Smart-phones and tablets need to be designed so that they can live with it. And power supplies needs to be designed to that they do not put out too much noise. Some details on this can be found at my EU standards for common mobile phone charger article.

Dealing with noise is an important aspect of any real-world electronic system, especially in a capacitive touchscreen in a cell phone or tablet. Noise Immunity of Touchscreen Devices web page tells that while there are many sources of noise that can interfere with capacitive touch sensing, the most prominent ones originate in displays and battery chargers. Cypress Offers Battery Charger Noise Immunity web page tells that low-cost chargers lack critical noise suppression components and can generate tens of volts (peak to peak) across the frequency spectrum of 1 Hz to 1 MHz. These voltage spikes can go directly into the touch panel during the presence of touch, severely impacting touch performance. Mobile phone vendors have worked together to create EN 62684 and EN301489, standards that regulate the noise spectrum for battery chargers.

Cypress Offers Battery Charger Noise Immunity web page tells touch screen controllers are developing all the time. It tells that a new TrueTouch feature Charger Armor enables touchscreens in mobile devices to function seamlessly by preventing inaccurate touch readings, which are often caused by common-mode noise from inexpensive chargers.

It is a good thing that those touch controllers are improving, because many people (electronics designers and users) struggle to overcome charger noise.


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