Electronic Engineering Crossword (Issue 268)

The answers to Circuit Cellar’s November electronics engineering crossword puzzle are now available.


2.     FLOWCODE—Columnist Jeff Bachiochi taught readers how to use this graphical programming language in his recent article about flowcharting (Circuit Cellar 266, 2012)

7.     LAPLACE—This type of transform is similar to Fourier, but expresses functions into moments as opposed of vibration

11.   RACEWAY—Channel to hold wires, cables, etc.

12.   SENSORSCircuit Cellar’s 250th issue (2011) focused on Measurement and this other topic

13.   LANDS—A metallic contact area

14.   BITTI—Interviewee (Circuit Cellar 253, 2011) who designed the “Witness Camera,” a self-recording surveillance camera

17.   DARLINGTON—This type of pair can be produced using individual transistors or purchased as a single device, as in a 2N6301

18.   WAFER—A slice of semiconductor material upon which monolithic ICs are produced

19.   DIELECTRICCORE—The insulating material that makes up the center of the cable through which the conductors are run [two words]

20.   THERMOPLASTIC—A synthetic, flexible mixture of rosins used as an insulting material


1.     ROUNDKEYS—In his article “Hardware-Accelerated Encryption” (Circuit Cellar 266, 2012) Patrick Schaumont said AES encryption’s real secrecy comes from the periodic additions of these

3.     OILCAN—A type of planar tube, similar to the lighthouse tube, which has cooling fins

4.     VECTORGRAPHICS—In the 1970s, Circuit Cellar founder Steve Ciarcia wrote his first article for BYTE about this topic

5.     VOLTAGECONTROLLED—An oscillator controlled by voltage input; there are usually two types: harmonic and relaxation [two words]

6.     TEMPEST—Describes compromising emanations

8.     ACQUISITIONTIME—In a communications system, the time interval required to attain synchronism [two words]

9.     INTEL—Company credited with making the first single-chip microprocessor

10.   HANDSHAKING—How one device communicates with one or more other devices, at a predetermined speed

15.   VARACTOR—Used as a capacitor to control voltage

16.   SALLENKEY—Active filer, two-pole [two words]


CC268: The History of Embedded Tech

At the end of September 2012, an enthusiastic crew of electrical engineers and journalists (and significant others) traveled to Portsmouth, NH, from locations as far apart as San Luis Obispo, CA,  and Paris, France, to celebrate Circuit Cellar’s 25th anniversary. Attendees included Don Akkermans (Director, Elektor International Media), Steve Ciarcia (Founder, Circuit Cellar), the current magazine staff, and several well-known engineers, editors, and columnists. The event marked the beginning of the next chapter in the history of this long-revered publication. As you’d expect, contributors and staffers both reminisced about the past and shared ideas about its future. And in many instances, the conversations turned to the content in this issue, which was at that time entering the final phase of production. Why? We purposely designed this issue (and next month’s) to feature a diversity of content that would represent the breadth of coverage we’ve come to deliver during the past quarter century. A quick look at this issue’s topics gives you an idea of how far embedded technology has come. The topics also point to the fact that some of the most popular ’80s-era engineering concerns are as relevant as ever. Let’s review.

In the earliest issues of Circuit Cellar, home control was one of the hottest topics. Today, inventive DIY home control projects are highly coveted by professional engineers and newbies alike. On page 16, Scott Weber presents an interesting GPS-based time server for lighting control applications. An MCU extracts time from GPS data and transmits it to networked devices.

The time-broadcasting device includes a circuit board that’s attached to a GPS module. (Source: S. Weber, CC268)

Thiadmer Riemersma’s DIY automated component dispenser is a contemporary solution to a problem that has frustrated engineers for decades (p. 26). The MCU-based design simplifies component management and will be a welcome addition to any workbench.

The DIY automated component dispenser. (Source: T. Riemersma, CC268)

USB technology started becoming relevant in the mid-to-late 1990s, and since then has become the go-to connection option for designers and end users alike. Turn to page 30 for Jan Axelson’s  tips about debugging USB firmware. Axelson covers controller architectures and details devices such as the FTDI FT232R USB UART controller and Microchip Technology’s PIC18F4550 microcontroller.

Debugging USB firmware (Source: J. Axelson, CC268)

Electrical engineers have been trying to “control time” in various ways since the earliest innovators began studying and experimenting with electric charge. Contemporary timing control systems are implemented in a amazing ways. For instance, Richard Lord built a digital camera controller that enables him to photograph the movement of high-speed objects (p. 36).

Security and product reliability are topics that have been on the minds of engineers for decades. Whether you’re working on aerospace electronics or a compact embedded system for your workbench (p. 52), you’ll want to ensure your data is protected and that you’ve gone through the necessary steps to predict your project’s likely reliability (p. 60).

The issue’s last two articles detail how to use contemporary electronics to improve older mechanical systems. On page 64 George Martin presents a tachometer design you can implement immediately in a machine shop. And lastly, on page 70, Jeff Bachiochi wraps up his series “Mechanical Gyroscope Replacement.” The goal is to transmit reliable data to motor controllers. The photo below shows the Pololu MinIMU-9.

The Pololu MinIMU-9′s sensor axes are aligned with the mechanical gyro so the x and y output pitch and roll, respectively. (Source: J. Bachiochi, CC268)

Issue 268: EQ Answers

Problem 1: A transformer’s windings, when measured individually (all other windings disconnected), have a certain amount of inductance. If you have a 1:1 transformer (both windings have the same inductance) and connect the windings in series, what value of inductance do you get?

Answer 1: Assuming you connect the windings in-phase, you’ll have double the number of turns, so the resulting inductance will be about four times the inductance of one winding alone.

If you hook them up out of phase, the inductance will cancel out and you’ll be left with the resistance of the wire and a lot of parasitic inter-winding capacitance.

Problem 2: If you connect the windings in parallel, what value of inductance do you get?

Answer 2: With the two windings connected in-phase and in parallel, the inductance will be exactly the same as the single-winding case. But the resulting inductor will be able to handle twice the current, as long as the core itself doesn’t saturate.

Question 3: Suppose you have a 32-bit word in your microprocessor, and you want to count how many contiguous strings ones that appear in it. For example, the word “01110001000111101100011100011111″ contains six such strings. Can you come up with an algorithm that uses simple shifts, bitwise logical and arithmetic operators, but —here’s the twist—does not require iterating over each bit in the word?

Answer 3: Here’s a solution that iterates over the number of strings, rather than the number of bits in the word.

int nstrings (unsigned long int x)
   int result = 0;

   /* convert x into a word that has a '1' for every
    * transition from 0 to 1 or 1 to 0 in the original
    * word.
   x ^= (x << 1);

   /* every pair of ones in the new word represents
    * a string of ones in the original word. Remove
    * them two at a time and keep count.
   while (x) {
     /* remove the lowest set bit from x; this
      * represents the start of a string of ones.
     x &= ~(x & -x);

     /* remove the next set bit from x; this
      * represents the end of that string of ones.
     x &= ~(x & -x);
   return result;

Problem 4: For the purpose of timing analysis, the operating conditions of an FPGA are sometimes known as “PVT,” which stands for “process, voltage, and temperature.” Voltage and temperature are pretty much self-explanatory, but what does process mean in this context?

Answer 4: The term process in this case refers to the manufacturing process at the plant where they make the FPGA. It’s a measure of the statistical variability of the physical characteristics from chip to chip as they come off the line.
This includes everything from mask alignment to etching times to doping levels. These things affect electrical parameters such as sheet and contact resistance, actual transistor gains, and thresholds and parasitic capacitances.
These kinds of variations are unavoidable, and the P in PVT is an attempt to account for their effects in the timing analysis. The idea is to make the analysis conservative enough so that your design will work reliably despite these variations.

Contributed by David Tweed