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imPARTing Knowledge 3: Understanding Component Engineering – Microcontrollers

October 26, 2011 | Comments | component engineering, consulting engineers, Douglas Alexander, electronic design, semiconductor, technology

By Steve Terry, SK Communications
Advisor to ComponentsEngineering.com

Many small board designs benefit nicely from the use of a microcontroller. But selecting an appropriate one for a particular design often brings on the feeling of “Where do I begin?”

This discussion limits its focus to low-end microcontrollers. For this purpose, we’ll stick with 8-bit devices. 8-bits simply means that internal processing only operates on 8 bits at a time. As one would expect, 16- and 32-bit micros would operate much faster as they are processing more bits of data with each instruction. To be sure, much of the same thinking applied to 8-bit microcontrollers can be applied to the 16- and 32-bit devices; however, cost, size, capabilities, performance, feature integration, and a host of other upscaled attributes quickly make it increasingly difficult to generalize on approach and applicability.

That said, even in the 8-bit microcontroller world, there are many highly specialized devices. So, to avoid confusion, we’ll leave that subject for a future discussion and stay with the garden variety parts for now. Quite often, if your design truly calls for one of these specialized micros, there’s not going to be much choice, and you’ll likely be familiar with those choices already, so you should be okay.

What is a microcontroller, anyway?

The key trait that distinguishes a microcontroller from a microprocessor is that it’s a microprocessor with a smorgasbord of built-in peripherals. For relatively simple board designs, such as controller boards, those embedded peripherals can save a lot on design effort and BOM (Bill of Materials) cost. Microcontrollers are commonly referred to as MCUs (for “microcontroller unit”); it’s nice and short and kinda rolls off your tongue, so we’ll use it here, too.

Base MCU feature sets typically include three types of memory (flash, RAM, and EEPROM), general purpose I/O (GPIO), support for various communications ports (UART, I2C, CAN, etc.), timers/PWMs, ADCs, DACs, internal oscillators, temperature sensors, and low power management. From there, the feature sets branch out widely. And this is really where the details come in to play for component selection.

Establishing requirements

With so many vendors and varieties of low-end micros, you may find it surprising that a good percentage of them will likely satisfy your design requirements. But even though so many will usually do the job, tailoring the selection tightly to your particular needs and preferences can make for a much smoother ride in the long run.

Generally, the first step is to define what functionality you must have. For example: How many GPIO pins? (always trying to include a few spare for those late design changes). How many ADC or DAC channels and with what resolution? Do you need timers or PWM control? How many? 8- or 16-bit?

How do you need to communicate to other devices on this board or another board, like I2C or SPI? Keep in mind that it’s always useful to bring a UART off the board for an RS232 debug port that you can connect to a terminal emulator on your PC. And any components added to the board to support it can generally be left off in volume production.

How much code space do you think you’ll need? And how much RAM? (Here, we don’t consider that you’ll need so much extra of either one that you’ll need to add external memory devices.) If you’re not really sure on memory requirements, err on the high side since:

1. running out of memory can seriously impose on the ability to implement those last few features the marketing guys said they really want included, and

2. you can generally downsize the part later if it turns out you have more memory than you need – maybe do this as part of a cost reduction board spin. Or, quite often (and if you plan it carefully), it will be a pin-compatible part, so it’s simply a BOM change.

And, well, there’s one more good reason that consistently proves prophetic:

3. Murphy’s Law Corollary: Code size grows to the size of available memory + 1 byte.

Feel like you’re ready to pick one? Read the rest at: element14.

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OctoBox eases testing of MIMO devices

October 17, 2011 | Comments | component engineering, consulting engineers, electronic design, technology

Dropped calls on cell phones due to faulty antenna placement have been selectively publicized, as in the case of the Apple iPhone 4G, but have been a common occurrence in all phones released in the past two years. Mobile carriers are putting heavy pressure on manufactures to avoid, if not eliminate the problem as soon as possible. No, actually they want it done now.

That puts the problem squarely in the laps of the test and measurement industry, which is meeting the demand with some alacrity as demand for the products increases and new technology boost speeds and transmission rates are coming online.

Of keen interest to product developers are compact solutions that test engineers can keep in their offices or at least within spitting distance. Companies like Agilent, Aeroflex and Anritsu are providing several desktop solutions. A small company in Boston, OctoScope, has pulled the wraps off a refrigerator-sized anechoic chamber, the OctoBox, that can test mobile devices without having to solder coax directly to the device antennae and deliver more real-world results.

“Lab testing with the devices’ actual antennas, even when the radios are not MIMO, is better than soldering coax to the antenna connections,” said Charles Gervasi, an engineer with Four Lakes Technology in Madison, Wisconsin. “For functional test in production, an over-the-air test is the only option. Automated test equipment can be configured to test multiple devices at once in the chamber.” (Read Gervasi’s full review of the OctoBox at element14.)

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See the entire article at Element14.com

imPARTing Knowledge 2: Resistors

September 29, 2011 | Comments | component engineering, consulting engineers, Douglas Alexander, electronic design, semiconductor, technology

By Douglas Alexander and Brian Steeves, CE Consultants
http://www.componentsengineering.com

My first up close and personal experience with a resistor was a 9V transistor radio in the middle of a Dodgers baseball game in 1959.

I was listening to the game in the fourth grade with the earphone wire snaked from my jeans’ front pocket, through my belt, (first historical use of a strain relief), under my sweater, up through the button hole in my collar, (second historical use of a strain relief), to insert the plug end, inconspicuously, as close as possible to my inner ear, cleverly designed to avoid the teacher’s detection.

All of a sudden, I began to smell something burning. Then I lost the audio entirely. At recess, I opened the back of my transistor radio to discover a cylindrical device with colored stripes printed around the cylinder with one of the two red stripes partially obliterated by a brown-black burn site that extended to the board and wiped out the “R” before the 10 label. I missed the end of the game but I did catch the end of my radio. Thus, my first experience with troubleshooting had begun with my nose and had ended with my eyes. Later in life, I heard my electronics professor telling me that I had discovered the first two steps for troubleshooting any circuit.

From that point on, I have developed a long-term professional relationship with the resistor, the most commonly used discrete device in electronics. The following is a discussion on some of the various resistor-based applications commonly in use today. This is not an exhaustive list, and the reader is invited to suggest other applications.

When placed in series with each other, with a tap connection between them, resistors are used as voltage dividers to produce a particular voltage from an input that is fixed or variable. This is one way to derive a bias voltage. The output voltage is proportional to that of the input and is usually smaller. Voltage dividers are useful for components that need to operate at a lesser voltage than that supplied by the input.

Resistors also help to filter signals used in oscillator circuits for video, audio, and many other clocked circuit devices. Used together with capacitors, this is known as an “RC” circuit, and the oscillation is a function of the two interacting to produce a time constant.

Because the flow of current through a resistor converts electrical energy into heat energy, the heat generated from the high resistance to the flow of the current is used commercially in the form of heating elements for irons, toasters, room heaters, electric stoves and ovens, dryers, coffee makers, and many other common household and industrial products. Similarly, it is the property of resistance that causes a filament to “glow” in light bulbs.

Current shunt resistors are low resistance precision resistors used to measure AC or DC electrical currents by the voltage drop those currents create across the resistance. Sometimes called an ammeter shunt, it is a type of current sensor.

Resistive power dividers or splitters have inherent characteristics that make them an excellent choice for certain applications, but unsuitable for others. In a lumped element divider, there is a 3dB loss in a simple two-way split. The loss numbers go up as the split count increases. Splitters can be used for both power and signal.

Resistors can be used in stepped configurations when they are tapped between multiple values or elements in a series. In the absence of a variable resistor (potentiometer), connecting to the various taps will allow for different fixed resistance values.

Using high-wattage wire-wound resistors as loads for 4-corner testing is a common practice in the qualification process of a power supply. By varying the line voltage and the resistive load to all four extremes, low line, high line, low load, and high load, a power supply’s operating limits can be determined.

(), invented and patented by the African-American Engineer Otis Boykin, are also ideal for compensating strain-gauge transducers. They offer the necessary accuracy and perform reliably at high temperatures. They are designed to minimize resistance value change, or to change in a controlled manner over different temperatures. Wire-Wound resistors are made by winding a length of wire on an insulating core. They can dissipate large power levels compared to other types and can be made with extremely tight resistance tolerances and controlled temperature characteristics.

Typically, a single, one-megaohm resistor is used with an antistatic or ESD wrist strap for safely grounding a person working on very sensitive electronic components or equipment. The wrist strap is connected to ground through a coiled, retractable cable with the 1 mega ohm resistorin series with ground. This allows for any high-voltage charges or transients to leak through to ground, preventing a voltage buildup on the technician’s body and thereby avoiding a component-damaging shock hazard when working with low-voltage tolerance parts. This Transient Resistor, formula symbol, is commonly referred to as a “mobile ohm”. These are usually designed in with a VoltsWagon pulling them.

Mobile Ohm, sans VW

Can I get a groan from someone? Author’s note: This is not an original pun, but I would rather diode than young. Author’s note: That was original. Sorry, I just couldn’t resist—or could I?

Passive terminators consist of a simple resistor. There are two types: (1) a resistor between signal and ground like in Ethernet, or (2) a resistor pair, one from the positive rail to signal with another from the signal to negative rail. Terminating resistors are widely used in paired transmission lines to prevent signal reflection.

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FPGA verification must address user uncertainty for prototyping, system validation

September 27, 2011 | Comments | electronic design, semiconductor, technology

By Loring Wirbel
Senior Correspondent, Footwasher Media

The recent expansion and diversification of the FPGA verification market bears a certain resemblance to the ASIC verification market of 20 years ago, though beset with opposite challenges, thanks to the changes wrought in 20 years by Moore’s Law. When companies such as Quickturn Systems created large logic emulation systems to verify ASICs in the early 1990s, users had to be convinced to spend significant amounts of money while dedicated floor space equivalent to a mainframe, all to verify system ASICs. Today, FPGA verification can be addressed in add-in boards for a workstation, or even in embedded test points within the FPGA itself.

But even as customers in 1990 were reticent to move to logic emulation due to price tags, today’s FPGA verification customer may show some trepidation because such systems may seem simplistic, invisible, or of questionable value. In many cases, however, FPGA users dare not commit to multiple-FPGA systems (or to ASICs prototyped with FPGAs) without these tools. Newer generations of FPGAs, incorporating the equivalent of millions of gates, integrate RISC CPUs, DSP blocks, lookaside co-processors, and high-speed on-chip interconnect. Verification of such designs is a necessity, not a luxury.

Click here to read the full text of the FPGA verification must address user uncertainty for prototyping, system validation article.

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