Circuit Cellar Newsletter Aug 2008

-AUGUST 2008-

Big Contest Returns from Unexpected Sources

Circuit Cellar analysts have been collecting data on sample distribution trends for nearly a decade. With over 100,000 sample MCUs and development tools placed through Circuit Cellar around the globe, and more than two dozen programs that track the conversion of a sample into a working embedded project, an interesting trend has emerged.

Although Circuit Cellar is a U.S.-based publication, it has a considerable international reach. This is most apparent at two points: during Design Contest sample distributions and during Design Contest project submission deadlines. Historically, over 60% of Circuit Cellar Design Contest projects have come from outside the United States. Sample distribution allocations follow a similar pattern.

But which non-U.S. countries are most efficient at converting a contest sample into a complete, unique embedded project for Circuit Cellar design contests? China tops the list, followed by Canada and New Zealand.

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Are You Ready For Embedded Hosting, Dual Role, and OTG USB?

By Jeff Bachiochi

Many of us are just coming to grips with supporting a USB interface as the communications medium of choice for our product designs. PC manufactures have eliminated the DB-9 (standard for years on every PC) with USB (and Firewire) connectors. We’ve been forced to learn more about the protocols than we ever wanted to know. Unless my product incorporates PC type architecture, I can’t take advantage of all the peripherals out there. So you can forget about adding a storage device, keyboard, or other USB peripheral to your project. Micros just don’t have the room to handle a USB host’s responsibilities.

USB OTG (On The Go) technology was announced on December 18^th 2001 by the USB Implementers Forum. Let’s see, that’s about seven years ago. You’d think by now that we would have access to all those USB products that have shipped to date, at least that was the promise made back then. About all that comes to mind might be some high priced digital camera that supports downloading directly into a printer. Hardly what I would call utopian connectivity.

Well, stand back, because the tools to make this a reality are finally here.

-Download Full Article-

Circuit Cellar Author Q & A

Peter Montgomery –Recurring Circuit Cellar Author

Editor’s Note: Watch for Peter’s next article in Circuit Cellar magazine’s September issue, “Dynamic Animatronic Remote (Part 1): Build A Custom Controller.” In the September issue, you’ll learn how Peter built a custom controller that enables him to remotely control his animatronic systems. Each piece of hardware is controlled by a separate computer program. The remote polls his laptop and builds menus that show the state of each program.

CC: Tell us a little bit about yourself (a bit more than what’s in your bio).

PETER: I live in Southern California. I currently work in the film business, primarily directing commercials and TV. I have also spent many, many years doing visual effects for feature films. In addition, I am a machinist, a welder and metal fabricator. I also play guitar, bass, and keyboards. I write music, sculpt, do car bodywork and restoration, etc. Basically, I do a lot of stuff. I never liked school, but I have always loved learning. I’ve been reading Circuit Cellar since Issue 2, I think. It would have been issue 1, but I subscribed too late and missed it. Like so many others, I also read Steve’s column in Byte before he started CC.

CC: You’ve described yourself as “self-taught in both programming and digital hardware.” What got you interested in embedded design and programming?

PETER: I’m a geek. I’ve always been interested in electronics and computers, as well as many other disciplines. If it involves making or modifying something creatively, I’m usually interested. I taught myself to program in BASIC in 1978 using a book at my high school library called, My Computer Likes Me When I Talk To It In BASIC. I later picked up 6502 Assembly programming by reading magazines and books. Around the time I entered college, I had an “a-ha!” moment where I realized that creating digital hardware was really like programming using chips. I’ve been doing both ever since.

The embedded side of things was always extremely interesting to me because I like gadgets, and I like making gadgets, and embedded programming is all about gadgets as far as I’m concerned. I was never a big fan of the “build a bunch of cool blinking lights” school of embedded programming. I tended toward problem solving and making things I wanted to use in either my personal or professional life.

CC: What was your first MCU-based design?

PETER: A 6502-based animation camera controller. This involved designing and laying out a 6502-based board with 8k RAM and 8 EPROM, along with the requisite address decoding, followed by a second board that generated multiple synchronized pulse streams for controlling stepper motors. The “joy” was that my debugging tools at the time consisted of a voltmeter, a logic probe, and an old transistor radio earphone. Believe it or not, since the pulse stream frequencies where in the audio range, I used to listen to the pulses with the earphone to see if things were working right. Later, I added a 4 × 20 character LCD to the system. This allowed me to debug by printing values on the LCD, much like some people use “printf” to debug C programs. Finally, I bought a 60-MHz scope at a swap meet. Life got much easier after that.

CC: Some of your real-time, motor-based systems have been used at Disney Studio’s optical department. Can you tell us about those designs? Why did you build them? What were the main parts that you used?

PETER: Up until 1993, pretty much the only way to combine multiple images for visual effects in movies was using a device called an optical printer. In its simplest form, this device is a big machine that has a 35-mm motion picture camera facing a 35-mm motion picture projector (each called a “head”) mounted to an extremely heavy base. The camera and projector can be run independently or in sync. When running in sync, it’s possible to re-photograph the film in the projector, while making changes to it. You can also add additional projector heads, with a common setup involving two projectors and one camera, all of which need to be able to run alone or together in any combination.

For decades, optical printers used big mechanical systems to run the cameras and projectors. Typically, this involved a large, free-running, washing-machine-style motor connected to a complex drive system of gears and clutches, allowing the operator to engage the cameras and projectors to the motor as needed. As you might imagine, it was hot, complicated, noisy, and prone to mechanical failure. During the 70s and 80s, people started converting these machines to use servo or stepper motors. Unfortunately, pretty much everyone who created systems to run optical printers were engineers who had never and would never use an optical printer. I was a rare exception in that I had run many optical printers and knew what would be useful in a control system for them, and I also was a programmer and hardware guy who could build the system.

The systems were 6502-based, and used TTL hardware to create the synchronized pulse streams. They had a number of features that made using them incredibly efficient for the operator. For example, all the heads could either be controlled manually or by using a custom keyboard that let you punch in a desired frame number that the computer would automatically seek to. Sometimes it was faster to just mash the buttons and sometimes it was faster to let the computer do the work via the keyboard. The system didn’t impose any rules on the operator as to how they could control the heads; it let that person decide on the fly what was the best use of their time.

Post-1993, the filmmaking community has turned to digital image manipulation more and more as the price became increasingly competitive. Optical printers are still in use, but their use has dropped to a very small amount overall.

CC: Next month, we will present the second part of this interview, in which Peter describes his most recent designs.

EQ Interactive

Question: What is the function of the circuit below?

Think You Have a Great EQ Challenge of Your Own?

E-mail your best EQ question and answer to eq@circuitcellar.com. The best EQs will be published by Circuit Cellar. Authors of the top four EQ picks will receive an Atmel In-Circuit Emulator mk-II.* All published EQs will earn the author a Certificate of Appreciation from Circuit Cellar.

-EQ Answer-

Microchip’s USB Connectivity Sample Zone

Be sure to sign up for a chance to receive exciting USB solutions from Microchip Technology.

www.circuitcellar.com/usb

EzPCB Offers 20% Discount to Microchip USB Sample Zone Participants

Microchip USB Sample Zone participants will be able to take advantage of a special offer from EzPCB. The offer may be used for PCB prototyping or for free components such as SMD resistors and capacitors as available through EzPCB’s service packages. http://www.ezpcb.com/

To make use of this offer, e-mail cathy@ezpcb.com and include the following:

1. Name

2. Email

3. Describe the basics of your project

4. Part number of Microchip IC

The title of the email should be "Circuit Cellar Microchip Samples."

Your First Propeller Program

An introduction to the new and exciting Parallax Propeller solution.

This chapter will begin the journey of using the Propeller. The topics include Clocks and Timing, Serial Communications, Important Programming Information, and adding the Propeller Accessory kit to the Propeller Proto Board. The programs in this chapter will be on the topic of Propeller-to-PC Communications using the USB to Serial Bridge, VGA and NTSC Video Outputs.

–Oliver Bailey, author of “Your First Propeller Program,” a preview chapter for Circuit Cellar readers who want to learn about the Propeller in detail. Copyright 2006, 2007, 2008 Timelines Industries. The complete work will be available for purchase exclusively through Parallax this October.

-Download “Your First Propeller Program”

Circuit Cellar Readership Survey

Please make sure you’ve taken Circuit Cellar’s annual reader survey. Your input, comments and questions not only help to define Circuit Cellar’s editorial goals, they also help us bring you the most on-target contests and sample distributions. Participants will also be entered for a chance to win Circuit Cellar CD-ROM archives.

-Reader Survey- http://www.circuitcellar.com/survey2008/

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Newsletter Archives

EQ Answer: The circuit is a logarithmic converter. The output voltage represents the logarithm of the input voltage (or current). Carefully constructed, this circuit can perform well over five decades or more of input (nanoamps to milliamps).

The collector current of a transistor is an exponential function of the base-emitter voltage, as defined by the Ebers-Moll equation:

I_S is the reverse saturation current of the base-collector junction, which is a function of transistor geometry, temperature, and other factors. V_T is kT/q, about 25.3 mV at room temperature. q is the electron charge (1.6E – 19 C). k is Boltzmann’s constant (1.38E – 23 J/K). T is absolute temperature (K).

Solving for V_BE yields:

This is the output of the first op-amp, which changes about 60 mV per decade of input current, but both V_T and I_S have a strong dependence on temperature. The second transistor, which has the same construction and is held at the same temperature as the first, is fed a constant reference level of collector current. This offsets the converter so that the output voltage is zero when the input current equals the reference current. The output voltage varies with the logarithm of the ratio I_IN/I_REF, with proportionality constant set by the gain of the second op-amp. A gain of 16 gives an output of –1 V per decade.

Note that the V_T factor in the V_BE equation has a dependency on temperature, which means that for input currents other than the reference current, there will be a scale factor error. The usual approach to addressing this is to incorporate a thermistor into the feedback network of the second op-amp so that its gain varies in such a way as to compensate for the varying scale factor.

*EQ award of Atmel In-Circuit Emulator mk-II: recipient responsible for any applicable duties and taxes. No cash alternative. Awards will be made at sole discretion of Circuit Cellar editorial staff. By submitting an EQ Q&A, Circuit Cellar is granted the right to publish the submitted material and the author’s name. Submissions must be original (not published in print or online previously).