What Is Correlation?

Interested in learning about correlation and how to implement it in a digital signal processing system? In Circuit Cellar 299, Robert Lacoste addresses the subject without going overboard with complicated mathematics. He explains how a simple correlation calculation can drastically improve a system’s performance.

Imagine a situation in which you have a noisy signal that includes replications of a given pattern. Each replication is more or less accurate, has a varying amplitude, and could be situated anywhere in the signal (see Figure 1). The pattern is known, even if it could have any shape. Also imagine that your boss or client asked you to find an algorithm that will locate each occurrence of the pattern in the signal and give an estimation of its amplitude. Not obvious, right? Well, it’s actually quite easy. This is a classic situation for which you can apply a simple mathematical operation: correlation.

Figure 1: This figure shows a given pattern (top) replicated two times in a noisy signal at different amplitudes (middle). The goal of the game is to identify the two replications (bottom).

Figure 1: This figure shows a given pattern (top) replicated two times in a noisy signal at different amplitudes (middle). The goal of the game is to identify the two replications (bottom).

Before I define correlation and explain how to implement it in a DSP system, let’s cover a few typical applications first. A radar system includes a transmitter and a receiver. The former sends out some pulses. The receiver must recognize the echoed pulses, which each corresponding to an obstacle. That’s exactly what a correlation is made for! Even if a radar is one of the best examples, there are thousands of other possible applications. Want to improve the performance of a sensor with information about the shape of the signal being detected? Use correlation. Need to identify a given vibration on an accelerometer-based system? Correlation is answer once again. The list is endless.


The good news about correlation is that the calculations are quite simple to explain and even simpler to implement in a software-based project or in an FPGA. Since I’m talking about digital systems, you can safely assume that the signal is digitized (by an analog-to-digital converter) and defined by N successive samples. Similarly, the pattern to be found is a set of M successive samples, which are also some numeric values. Let’s assume that the pattern is shorter than the input signal so that M < N. How should you proceed?

The correlation calculation works as follows. Start by positioning the pattern above the first M points of the signal. For each sample of the pattern, multiply the corresponding pattern and signal values and then sum all the results. You’ve got the first point of the correlation. Then shift the pattern by one sample on the right and do the same calculation again to find the second point of the correlation. Continue up to the end of the signal and you’ve got the correlation of the pattern and signal, which has N – M + 1 points in that case. Refer to Listing 1 if you prefer pseudocode to a description (assuming the index are numbered from 0 to N – 1).

Listing 1: This pseudo-code implements the correlation algorithmtion

Listing 1: This pseudo-code implements the correlation algorithm.

Very simple, right? The process is illustrated on Figure 2. How does this calculation answer to our problem? Very simply: The calculated correlation is higher when the signal and pattern matches.

Figure 2: A correlation works by progressively shifting the pattern (middle relatively to the signal (top). At each position, the two curves are multiplied term-by-term and summed, giving one point on the resulting correlation (bottom).

Figure 2: A correlation works by progressively shifting the pattern (middle relatively to the signal (top). At each position, the two curves are multiplied term-by-term and summed, giving one point on the resulting correlation (bottom).

So you have just to locate peaks on the calculated correlation. The position of the peaks shows where the pattern are located in the signal, and their amplitudes are directly proportional to the amplitude of the replica.—Robert Lacoste (Circuit Cellar 299, 2015)

This article appears in Circuit Cellar 299 (June 2015).

Quad Channel DPWM Step-Down Controller

Exar Corp. has introduced the XR77128, a universal PMIC that drives up to four independently controlled external DrMOS power stages at currents greater than 40 A for the latest 64-bit ARM processors, FPGAs, DSPs and ASICs. DrMOS technology is quickly growing in popularity in telecom and networking applications. These same applications find value in Exar’s Programmable Power technology which allows low component count, rapid development, easy system integration, dynamic control and telemetry. Depending on output current requirements, each output can be independently configured to directly drive external MOSFETs or DrMOS power stages.EX045_XR77128

The XR77128 is quickly configured to power nearly any FPGA, SoC, or DSP system through the use of Exar’s design tool, PowerArchitect, and programmed through an I²C-based SMBus compliant serial interface. It can also monitor and dynamically control and configure the power system through the same I²C interface. Five configurable GPIOs allow for fast system integration for fault reporting and status or for sequencing control.  A new Arduino-based development platform allows software engineers to begin code development for telemetry and dynamic control long before their hardware is available.

The XR77128 is available in a RoHS-compliant, green/halogen free space-saving 7 mm × 7 mm TQFN. It costs $7.75 in 1000-piece quantities.

Source: Exar Corp.

Industry’s Smallest Dual 3A/Single 6A Step-Down Power Module

Intersil Corp. recently announced the ISL8203M, a dual 3A/single 6A step-down DC/DC power module that simplifies power supply design for FPGAs, ASICs, microprocessors, DSPs, and other point of load conversions in communications, test and measurement, and industrial systems. The module’s compact 9.0 mm × 6.5 mm × 1.83 mm footprint combined with industry-leading 95% efficiency provides power system designers with a high-performance, easy-to-use solution for low-power, low-voltage applications.INT0325_ISL8203M_Intersil_Power_Module The ISL8203M is a complete power system in an encapsulated module that includes a PWM controller, synchronous switching MOSFETs, inductors and passive components to build a power supply supporting an input voltage range of 2.85 to 6 V. With an adjustable output voltage between 0.8 and 5 V, you can use one device to build a single 6-A or dual output 3-A power supply.

Designed to maximize efficiency, the ISL8203M power module offers best-in-class 15° C/W thermal performance and delivers 6 A at 85°C without the need for heatsinks or a fan. The ISL8203M leverages Intersil’s patented technology and advanced packaging techniques to deliver high power density and the best thermal performance in the industry, allowing the ISL8203M to operate at full load over a wide temperature range. The power module also provides over-temperature, over-current and under-voltage lockout protection, further enhancing its robustness and reliability.

Features and specifications:
•       Dual 3-A or single 6-A switching power supply
•       High efficiency, up to 95°
•       Wide input voltage range: 2.85 to 6 V
•       Adjustable output range: 0.8 to 5 V
•       Internal digital soft-start: 1.5 ms
•       External synchronization up to 4 MHz
•       Overcurrent protection

The ISL8203M power module is available in a 9 mm × 6.5 mm, QFN package. It costs $5.97 in 1,000-piece quantities. The ISL8203MEVAL2Z evaluation costs $67.

Source: Intersil

Diode Bridge Solution (EE Tip #140)

Once I connected a battery up to a DSP in the wrong “direction,” thereby destroying the DSP. That incident drove home the necessity of “suspenders and belt” design.Diode

After the accident, my colleague and I added a diode to the circuit to make it impossible to repeat that mistake. Nowadays, when I teach elementary electronics courses, I generally mention the diode bridge as a way to make it possible to connect up a battery in either “direction” without endangering the electronics to which the battery is to be connected.

My mistake has served as a cautionary tale for many years now.—Shlomo Engelberg, CC25, 2013

New DSP “Lab-in-a-Box” for ARM-Based Audio Systems

Cambridge, UK-based, ARM and its partners will start shipping a DSP “Lab-in-a-Box” (LiB) to universities worldwide to help boost practical skills development and the creation of new ARM-based audio systems. This will include products such as high-definition home media and voice-controlled home automation systems. The LiB kits contain ARM Cortex-M4-based microcontroller boards by STMicroelectronics and audio cards from Wolfson Microelectronics and Farnell element14.ARMDSPLiBWeb

As the centerpiece of the ARM University Program, LiB packages offer ARM-based technology and high-quality teaching and training materials that support electronics and computer engineering courses. DSP courses have traditionally used software simulation packages, or hands-on labs using relatively expensive development kits costing around $300 per student. By comparison, this new DSP LiB will cost around $50 and will allow students to practice theory with advanced hardware sourced from widely-available products.

“Our Lab-in-a-Box offerings are proving hugely popular in universities because of the low-cost access to state-of-the-art technology,” said Khaled Benkrid, manager of the Worldwide University Program, ARM. “The DSP kits, powered by ARM Cortex-M4-based processors, enable high performance yet energy-efficient digital signal processing at a very affordable price. We expect to see them being used by students to create commercially-viable audio applications and it’s another great example of our partnership supporting engineers in training and beyond.”

The DSP LiB will begin shipping to universities in July 2014. It is the latest in a series of initiatives led by ARM which span multiple academic topics including embedded systems design, programming and SoC design. The DSP kits will also be offered to developers outside academia at a later date.

[via audioXpress.com]

DSP vs. RISC Processors (EE Tip #110)

There are a few fundamental differences between DSP and RISC processors. One difference has to do with arithmetic. In the analog domain, saturation, or clipping, isn’t recommended. But it generally comes with a design when, for example, an op-amp is driven high with an input signal. In the digital domain, saturation should be prevented because it causes distortion of the signal being analyzed. But some saturation is better than overflow or wrap-around. Generally speaking, a RISC processor will not saturate, but a DSP will. This is an important feature if you want to do signal processing.

Let’s take a look at an example. Consider a 16-bit processor working with unsigned numbers. The minimum value that can be represented is 0 (0x0000), and the maximum is 65535 (0xFFFF). Compute:

out = 2 × x

where x is an input value (or an intermediate value in a series of calculations). With a generic processor, you’re in trouble when x is greater than 32767.

If x = 33000 (0x80E8), the result is out = 66000 (0x101D0). Because this value can’t be represented with 16 bits, the out = 2 × x processor will truncate the value:

out = 2 × 333000 = 464(0x01D0)

From that point on, all the calculations will be off. On the other end, a DSP (or an arithmetic unit with saturation) will saturate the value to its maximum (or minimum) capability:

out = 2 × 333000 = 65535(0xFFFF)

In the first case, looking at out, it would be wrong to assume that x is a small value. With saturation, the out is still incorrect, although it accurately shows that the input is a large number. Trends in the signal can be tracked with saturation. If the saturation isn’t severe (affecting only a few samples), the signal might be demodulated correctly.

Generic RISC processors like the NXP (Philips) LPC2138 don’t have a saturation function, so it’s important to ensure that the input values or the size of the variable are scaled correctly to prevent overflow. This problem can be avoided with a thorough simulation process.—Circuit Cellar 190, Bernard Debbasch, “ARM-Based Modern Answering Machine,” 2006.

This piece originally appeared in Circuit Cellar 190, 2006. 

Processing, Wiring, and Arduino (EE Tip 101)

Processing is a language and an open-source programming environment for programming images, animations, and interactions. The project, an initiative from Ben Fry and Casey Reas, is based on ideas developed by the Aesthetics and Computation Group of the MIT Media Lab. Processing was created in order to teach the fundamentals of programming in a visual context and to serve as a sketchbook or professional software production tool. Processing runs under GNU/Linux, Mac OS X, and Windows. Several books have already been written on Processing.

Source: Clemens Valens, “Microcontrollers for Dummes,” 080931-I, Elektor, 2/2009.

Source: Clemens Valens, “Microcontrollers for Dummes,” 080931-I, Elektor, 2/2009.

Just like Arduino, Wiring is a programming environment with microcontroller board for exploring electronic arts, teaching programming, and quick prototyping. Wiring, programmed in Processing, is an initiative by Hernando Barragán and was designed at the Interaction Design Institute Ivrea (IDII) in Italy.

Arduino is a fast, open-source electronic prototyping platform. Arduino is aimed at DIYers, electronics enthusiasts, and anyone interested in creating objects or interactive environments. Created by Massimo Banzi, Gianluca Martino, David Cuartielles, and David Mellis, Arduino uses a programming language based on Processing. Arduino may be regarded as a simplification of Wiring.

For more information, refer to Clemens Valens’s article, “Microcontrollers for Dummies,” 080931-I, Elektor, 2/2009.

NXP LPC800 Microcontroller Challenge

Attention microcontroller users around the world! Ready to enter NXP Semiconductor’s LPC800 Challenge? Getting started is straightforward.

Elektor and Circuit Cellar have partnered with NXP Semiconductors to promote the Challenge. Once you have your LPC800 mini-board and code, you simply register and start working. The rules and complete details are listed on the LPC800 Challenge webpage.

The entry deadline is August 30, 2013. Once all the entries are received, NXP will select the most unique, interesting and funny submissions to receive a LPC800 LPCXpresso development kit.

The LPC800 is an ARM Cortex-M0+-based, 32-bit microcontroller operating at CPU frequencies of up to 30 MHz. The LPC800 supports up to 16 KB of flash memory and 4 KB of SRAM. The peripheral complement of the LPC800 includes a CRC engine, one I2C-bus interface, three USARTs, two SPI interfaces, one multi-purpose, state-configurable timer, one comparator, function-configurable I/O ports through a switch matrix, and up to 18 general purpose I/O pins.

Need design ideas? Check out these microcontroller projects with NXP parts.

Microcontroller-Based Heating System Monitor

Checking a heating system’s consumption is simple enough.

Heating system monitor

Determining a heating system’s output can be much more difficult, unless you have this nifty design. This Atmel ATmega microcontroller-based project enables you to measure heat output as well as control a circulation pump.

Heating bills often present unpleasant surprises. Despite your best efforts to economise on heating, they list tidy sums for electricity or gas consumption. In this article we describe a relatively easy way to check these values and monitor your consumption almost continuously. All you need in order to determine how much heat your system delivers is four temperature sensors, a bit of wiring, and a microcontroller. There’s no need to delve into the electrical or hydraulic components of your system or modify any of them.

A bit of theory
As many readers probably remember from their physics lessons, it’s easy to calculate the amount of heat transferred to a medium such as water. It is given by the product of the temperature change ΔT, the volume V of the medium, and the specific heat capacity CV of the medium. The power P, which is amount of energy transferred per unit time, is:

P= ΔT × CV × V // Δt

With a fluid medium, the term V // Δt can be interpreted as a volumetric flow Vt. This value can be calculated directly from the flow velocity v of the medium and the inner diameter r of the pipe. In a central heating system, the temperature difference ΔT is simply the difference between the supply (S) and return (R) temperatures. This yields the formula:

P = (TS – TR) × CV × v × pr2

The temperatures can easily be measured with suitable sensors. Flow transducers are available for measuring the flow velocity, but installing a flow transducer always requires drilling a hole in a pipe or opening up the piping to insert a fitting.

Measuring principle
Here we used a different method to determine the flow velocity. We make use of the fact that the supply and return temperatures always vary by at least one to two degrees due to the operation of the control system. If pairs of temperature sensors separated by a few metres are mounted on the supply and return lines, the flow velocity can be determined from the time offset of the variations measured by the two sensors…

As the water flows through the pipe with a speed of only a few metres per second, the temperature at sensor position S2 rises somewhat later than the temperature at sensor position S, which is closer to the boiler.

An ATmega microcontroller constantly acquires temperature data from the two sensors. The time delay between the signals from a pair of sensors is determined by a correlation algorithm in the signal processing software, which shifts the signal waveforms from the two supply line sensors relative to each other until they virtually overlap.The temperature signals from the sensors on the return line are correlated in the same manner, and ideally the time offsets obtained for the supply and return lines should be the same.

To increase the sensitivity of the system, the return line sensor signals are applied to the inputs of a differential amplifier, and the resulting difference signal is amplified. This difference signal is also logged as a function of time. The area under the curve of the difference signal is a measure of the time offset of the temperature variations…

Hot water please
If the heating system is also used to supply hot water for domestic use, additional pipes are used for this purpose. For this reason, the PCB designed by the author includes inputs for additional temperature sensors. It also has a switched output for driving a relay that can control a circulation pump.

Under certain conditions, controlling the circulation pump can save you a lot of money and significantly reduce CO2 emissions. This is because some systems have constant hot water circulation so users can draw hot water from the tap immediately. This costs electricity to power the pump, and energy is also lost through the pipe walls. This can be remedied by the author’s circuit, which switches on the circulation pump for only a short time after the hot water tap is opened. This is detected by the temperature difference between the hot water and cold water supply lines…

Circuit description
The easiest way to understand the schematic diagram is to follow the signal path. It starts at the temperature sensors connected to the circuit board, which are NTC silicon devices.

Heating system monitor schematic

Their resistance varies by around 0.7–0.8% per degree K change in temperature. For example, the resistance of a KT110 sensor is approximately 1.7 kΩ at 5 °C and approximately 2.8 kΩ at 70 °C.

The sensor for supply temperature S forms a voltage divider with resistor R37. This is followed by a simple low-pass filter formed by R36 and C20, which filters out induced AC hum. U4a amplifies the sensor signal by a factor of approximately 8. The TL2264 used here is a rail-to-rail opamp, so the output voltage can assume almost any value within the supply voltage range. This increases the absolute measurement accuracy, since the full output signal amplitude is used. U4a naturally needs a reference voltage on its inverting input. This is provided by the combination of R20, R26 and R27. U5b acts as an impedance converter to minimise the load on the voltage divider…

Thermal power

PC connection
The circuit does not have its own display unit, but instead delivers its readings to a PC via an RS485 bus. Its functions can also be controlled from the PC. IC U8 looks after signal level conversion between the TTL transmit and receive lines of the ATmega microcontroller’s integrated UART and the differential RS485 bus. As the bus protocol allows several connected (peer) devices to transmit data on the bus, transmit mode must be selected actively via pin 3. Jumper JP3 must be fitted if the circuit is connected to the end of the RS485 bus. This causes the bus to be terminated in 120 Ω, which matches the characteristic impedance of a twisted-pair line…

[Via Elektor-Projects.com]

Infrared Communications for Atmel Microcontrollers

Are you planning an IR communications project? Do you need to choose a microcontroller? Check out the information Cornell University Senior Lecturer Bruce Land sent us about inexpensive IR communication with Atmel ATmega microcontrollers. It’s another example of the sort of indispensable information covered in Cornell’s excellent ECE4760 course.

Land informed us:

I designed a basic packet communication scheme using cheap remote control IR receivers and LED transmitters. The scheme supports 4800 baud transmission,
with transmitter ID and checksum. Throughput is about twenty 20-character packets/sec. The range is at least 3 meters with 99.9% packet receive and moderate (<30 mA) IR LED drive current.

On the ECE4760 project page, Land writes:

I improved Remin’s protocol by setting up the link software so that timing constraints on the IR receiver AGC were guaranteed to be met. It turns out that there are several types of IR reciever, some of which are better at short data bursts, while others are better for sustained data. I chose a Vishay TSOP34156 for its good sustained data characteristics, minimal burst timing requirements, and reasonable data rate. The system I build works solidly at 4800 baud over IR with 5 characters of overhead/packet (start token, transmitter number, 2 char checksum , end token). It works with increasing packet loss up to 9000 baud.

Here is the receiver circuit.

The receiver circuit (Source: B. Land, Cornell University ECE4760 Infrared Communications
for Atmel Mega644/1284 Microcontrollers)

Land explains:

The RC circuit acts a low-pass filter on the power to surpress spike noise and improve receiver performance. The RC circuit should be close to the receiver. The range with a 100 ohm resistor is at least 3 meters with the transmitter roughly pointing at the receiver, and a packet loss of less then 0.1 percent. To manage burst length limitations there is a short pause between characters, and only 7-bit characters are sent, with two stop bits. The 7-bit limit means that you can send all of the printing characters on the US keyboard, but no extended ASCII. All data is therefore sent as printable strings, NOT as raw hexidecimal.

Land’s writeup also includes a list of programs and packet format information.

Electrostatic Cleaning Robot Project

How do you clean a clean-energy generating system? With a microcontroller (and a few other parts, of course). An excellent example is US designer Scott Potter’s award-winning, Renesas RL78 microcontroller-based Electrostatic Cleaning Robot system that cleans heliostats (i.e., solar-tracking mirrors) used in solar energy-harvesting systems. Renesas and Circuit Cellar magazine announced this week at DevCon 2012 in Garden Grove, CA, that Potter’s design won First Prize in the RL78 Green Energy Challenge.

This image depicts two Electrostatic Cleaning Robots set up on two heliostats. (Source: S. Potter)

The nearby image depicts two Electrostatic Cleaning Robots set up vertically in order to clean the two heliostats in a horizontal left-to-right (and vice versa) fashion.

The Electrostatic Cleaning Robot in place to clean

Potter’s design can quickly clean heliostats in Concentrating Solar Power (CSP) plants. The heliostats must be clean in order to maximize steam production, which generates power.

The robot cleaner prototype

Built around an RL78 microcontroller, the Electrostatic Cleaning Robot provides a reliable cleaning solution that’s powered entirely by photovoltaic cells. The robot traverses the surface of the mirror and uses a high-voltage AC electric field to sweep away dust and debris.

Parts and circuitry inside the robot cleaner

Object oriented C++ software, developed with the IAR Embedded Workbench and the RL78 Demonstration Kit, controls the device.

IAR Embedded Workbench IDE

The RL78 microcontroller uses the following for system control:

• 20 Digital I/Os used as system control lines

• 1 ADC monitors solar cell voltage

• 1 Interval timer provides controller time tick

• Timer array unit: 4 timers capture the width of sensor pulses

• Watchdog timer for system reliability

• Low voltage detection for reliable operation in intermittent solar conditions

• RTC used in diagnostic logs

• 1 UART used for diagnostics

• Flash memory for storing diagnostic logs

The complete project (description, schematics, diagrams, and code) is now available on the Challenge website.


The Future of 8-Bit Chips (CC 25th Anniversary Preview)

Ever since the time when a Sony Walkman retailed for around $200, engineers of all backgrounds and skill levels have been prognosticating the imminent death of 8-bit chips. No matter your age, you’ve likely heard the “8-bit is dead” argument more than once. And you’ll likely hear it a few more times over the next several years.

Long-time Circuit Cellar contributor Tom Cantrell has been following the 8-bit saga for the last 25 years. In Circuit Cellar‘s 25th Anniversary issue, he offers his thoughts on 8-bit chips and their future. Here’s a sneak peek. Cantrell writes:

“8-bit is dead.”  Or so I was told by a colleague. In 1979. Ever since then, reports of the demise of 8-bit chips have been greatly, and repeatedly, exaggerated. And ever since then, I’ve been pointing out the folly of premature eulogizing.

I’ll concede the prediction is truer today than in 1979—mainly, because it wasn’t true at all then. Now, some 30-plus years later, let’s reconsider the prospects for our “wee” friends…

Let’s start the analysis by putting on our Biz101 hats. If you Google “Product Life Cycle” and click on “Images,” you’ll see a variety of somewhat similar graphs showing how products pass through stages of growth, maturity, and decline. Though all the graphs tell a rise-and-fall story, it’s interesting to note the variations. Some show a symmetrical life cycle that looks rather like a normal distribution. But the majority of the graphs show a “long-tail” variation in which the maturity phase lasts somewhat longer and the decline is relatively gradual.

Another noteworthy difference is how some graphs define life and death in terms of “sales” and others “profits.” It stands to reason that no business will continue to sell at a loss indefinitely, but the market knows how to fix that. Even if some suppliers wave the white flag, those that remain can raise prices and maintain profitability as long as there is still demand.

One of the more interesting life cycle variations shows that innovation, like a fountain of youth, can stave off death indefinitely. An example that comes to mind is the recent introduction of ferroelectric RAM (FRAM) MCUs. FRAM has real potential to reduce power consumption and also streamlines the supply chain because a single block of FRAM can be arbitrarily partitioned to emulate any mix of read-mostly or random access memory (see Photo 1). They may be “mature” products, but today the Texas Instruments MSP430 and Ramtron 8051 are leading the way with FRAM.

Photo 1: Ongoing innovation, such as the FRAM-based “Wolverine” MCU from Texas Instruments, continues to expand the market for mini-me MCUs. (Source: Cantrell CC25)

And “innovation” isn’t limited to just the chips themselves. For instance, consider the growing popularity of the Arduino SBC. There’s certainly nothing new about the middle-of-the-road, 8-bit Atmel AVR chip it uses. Rather, the innovations are with the “tools” (simplified IDE), “open-source community,” and “sales channel” (e.g., RadioShack). You can teach an old chip new tricks!

Check out the upcoming anniversary issue for the rest of Cantrell’s essay. Be sure to let us know what you think about the future of the 8-bit chip.

Do Small-RAM Devices Have a Future? (CC 25th Anniversary Preview)

What does the future hold for small-RAM microcontrollers? Will there be any reason to put up with the constraints of parts that have little RAM, no floating point, and 8-bit registers? The answer matters to engineers who have spent years programming small-RAM MCUs. It also matters to designers who are hoping to keep their skills relevant as their careers progress in the 21st century.

In the upcoming Circuit Cellar 25th Anniversary Issue—which is slated for publication in early 2013—University of Utah professor John Regehr shares his thoughts on the future of small-RAM devices. He writes:

For the last several decades, the role of small-RAM microcontrollers has been clear: they are used to perform fixed (though sometimes very sophisticated) functionality in environments where cost, power consumption, and size need to be minimized. They exploit the low marginal cost of additional transistors to integrate volatile RAM, nonvolatile RAM, and numerous peripherals into the same package as the processor core, providing a huge amount of functionality in a small, cheap package. Something that is less clear is the future of small-RAM microcontrollers. The same fabrication economics that make it possible to put numerous peripherals on a single die also permit RAM to be added at little cost. This was brought home to me recently when I started using Raspberry Pi boards in my embedded software class at the University of Utah. These cost $25 to $35 and run a full-sized Linux distribution including GCC, X Windows, Python, and everything else—all on a system-on-chip with 256 MB of RAM that probably costs a few dollars in quantity.

We might ask: Given that it is already the case that a Raspberry Pi costs about the same as an Arduino board, in the future will there be any reason to put up with the constraints of an architecture like Atmel’s AVR, where we have little RAM, no floating point, and 8-bit registers? The answer matters to those of us who enjoy programming small-RAM MCUs and who have spent years fine-tuning our skills to do so. It also matters to those of us who hope to keep our skills relevant through the middle of the 21st century. Can we keep writing C code, or do we need to start learning Java, Python, and Haskell? Can we keep writing stand-alone “while (true)” loops, or will every little MCU support a pile of virtual machines, each with its own OS?

Long & Short Term

In the short term, it is clear that inertia will keep the small-RAM parts around, though increasingly they will be of the more compiler-friendly varieties, such as AVR and MSP430, as opposed to earlier instruction sets like Z80, HC11, and their descendants. But will small-RAM microcontrollers exist in the longer term (e.g., 25 or 50 years)? I’ll attempt to tackle this question by separately discussing the two things that make small-RAM parts attractive today: their low cost and their simplicity.

If we assume a cost model where packaging and soldering costs are fixed but the marginal cost of a transistor (not only in terms of fabrication, but also in terms of power consumption) continues to drop, then small-RAM parts will eventually disappear. In this case, several decades from now even the lowliest eight-pin package, costing a few pennies, will contain a massive amount of RAM and will be capable of running a code base containing billions of lines…

Circuit Cellar’s Circuit Cellar 25th Anniversary Issue will be available in early 2013. Stay tuned for more updates on the issue’s content.

CC269: Break Through Designer’s Block

Are you experiencing designer’s block? Having a hard time starting a new project? You aren’t alone. After more than 11 months of designing and programming (which invariably involved numerous successes and failures), many engineers are simply spent. But don’t worry. Just like every other year, new projects are just around the corner. Sooner or later you’ll regain your energy and find yourself back in action. Plus, we’re here to give you a boost. The December issue (Circuit Cellar 269) is packed with projects that are sure to inspire your next flurry of innovation.

Turn to page 16 to learn how Dan Karmann built the “EBikeMeter” Atmel ATmega328-P-based bicycle computer. He details the hardware and firmware, as well as the assembly process. The monitoring/logging system can acquire and display data such as Speed/Distance, Power, and Recent Log Files.

The Atmel ATmega328-P-based “EBikeMeter” is mounted on the bike’s handlebar.

Another  interesting project is Joe Pfeiffer’s bell ringer system (p. 26). Although the design is intended for generating sound effects in a theater, you can build a similar system for any number of other uses.

You probably don’t have to be coerced into getting excited about a home control project. Most engineers love them. Check out Scott Weber’s garage door control system (p. 34), which features a MikroElektronika RFid Reader. He built it around a Microchip Technology PIC18F2221.

The reader is connected to a breadboard that reads the data and clock signals. It’s built with two chips—the Microchip 28-pin PIC and the eight-pin DS1487 driver shown above it—to connect it to the network for testing. (Source: S. Weber, CC269)

Once considered a hobby part, Arduino is now implemented in countless innovative ways by professional engineers like Ed Nisley. Read Ed’s article before you start your next Arduino-related project (p. 44). He covers the essential, but often overlooked, topic of the Arduino’s built-in power supply.

A heatsink epoxied atop the linear regulator on this Arduino MEGA board helped reduce the operating temperature to a comfortable level. This is certainly not recommended engineering practice, but it’s an acceptable hack. (Source: E. Nisley, CC269)

Need to extract a signal in a noisy environment? Consider a lock-in amplifier. On page 50, Robert Lacoste describes synchronous detection, which is a useful way to extract a signal.

This month, Bob Japenga continues his series, “Concurrency in Embedded Systems” (p. 58). He covers “the mechanisms to create concurrently in your software through processes and threads.”

On page 64, George Novacek presents the second article in his series, “Product Reliability.” He explains the importance of failure rate data and how to use the information.

Jeff Bachiochi wraps up the issue with a article about using heat to power up electronic devices (p. 68). Fire and a Peltier device can save the day when you need to charge a cell phone!

Set aside time to carefully study the prize-winning projects from the Reneas RL78 Green Energy Challenge (p. 30). Among the noteworthy designs are an electrostatic cleaning robot and a solar energy-harvesting system.

Lastly, I want to take the opportunity to thank Steve Ciarcia for bringing the electrical engineering community 25 years of innovative projects, essential content, and industry insight. Since 1988, he’s devoted himself to the pursuit of EE innovation and publishing excellence, and we’re all better off for it. I encourage you to read Steve’s final “Priority Interrupt” editorial on page 80. I’m sure you’ll agree that there’s no better way to begin the next 25 years of innovation than by taking a moment to understand and celebrate our past. Thanks, Steve.

Microcontroller-Based Markov Music Box

Check out the spectrogram for two FM notes produced by FM modulation. Red indicates higher energy at a given time and frequency.

Cornell University senior lecturer Bruce Land had two reasons for developing an Atmel AVR micrcontroller-based music box. One, he wanted to present synthesis/sequencing algorithms to his students. And two, he wanted the challenge of creating an interactive music box. Interactive audio is becoming an increasingly popular topic among engineers and designers, as we recently reported.

Land writes:

Traditional music boxes play one or two tunes very well, but are not very interactive. Put differently, they have a high quality of synthesis, but a fixed-pattern note sequencer and fixed tonal quality. I wanted to build a device which would play an interesting music-like note sequence, which constantly changed and evolved, with settable timbre, tempo, and beat… To synthesize nice sounding musical notes you need to control spectral content of the note, the rise time (attack), fall time (decay), and the change in spectral content during attack and decay.  Also it is nice to have at least two independent musical voices. And all of this has to be done using the modest arithmetic capability of an 8-bit microcontroller.

Land’s students subsequently used the music box for other projects, such as an auto-composing piano, as shown in the following video.

In early 2013 Circuit Cellar will run Land’s in-depth article on the Markov music box project. Stay tuned for more information.