Arduino-Based DIY Voltage Booster (EE Tip #117)

If your project needs a higher voltage rail than is already available in the circuit, you can use an off-the-shelf step-up device. But when you want a variable output voltage, it’s less easy to find a ready-made IC. However, it’s not complicated to build such a circuit yourself, especially if you have a microcontroller board that’s as easy to program as an Arduino. And this also lets you experiment with the circuit so you can get a better understanding of how it works.

Source: Elektor, April 2010

Source: Elektor, April 2010

No surprises in the circuit—a largely conventional boost converter. The MOSFET is driven by a pulse width modulated (PWM) signal from the microcontroller, and the output voltage is measured by one of the microcontroller’s analog inputs. The driver adjusts the PWM signal according to the difference between the output voltage measured and the voltage wanted.

We don’t have enough space here to go into details about how this circuit works, but it’s worth mentioning a few points of special interest.

The small capacitor across the diode improves the efficiency of the circuit. The load is represented by R3. The components used make it possible to supply over 1 A (current limited by the MSS1260T 683MLB inductor from Coilcraft), but maximum efficiency (89%) is at around 95 mA (at an output voltage of 10 V). To avoid damaging the controller’s analog input (≤5 V), the output voltage may not exceed 24 V. For higher voltages, the values of resistors R1 and R2 would need to be changed.

The MOSFET is driven by the microcontroller, which is nothing but a little Arduino board. The Arduino’s default PWM signal frequency is around 500 Hz—too low for this application, which needs a frequency at least 100 times higher. So we can’t use the PWM functions offered by Arduino. But that’s no problem, as the Arduino can also be programmed in assembler, allowing a maximum frequency of 62.5 kHz (the microcontroller runs at 16 MHz). To sample the output voltage, a frequency of 100 Hz is acceptable, which means we can use Arduino’s standard timers and analog functions. The Arduino serial port is very handy: we can use it for sending the output voltage set point (5–24 V) and for collecting certain information about the operation. Thanks to the Arduino environment, it only took about half an hour to program. Software is available. — Clemens Valens (Elektor, April 2010)

Electronics Grounding (EE Tip #107)

Whether you are professional electrical engineer or part-time DIYer, before you start your next project, read through this primer on grounding. This short survey covers one of the most fundamental topics in electronics: grounding.

Electronics Signal Ground or Circuit Common

Signal ground is the current return to the power supply. Current leaves the power supply, passes through the various electronic components, and then returns to the supply. The typical symbol for signal ground is shown in Figure 1.EE107-F1-2

 Chassis Ground or Earth Ground

Chassis ground is an electrical safety requirement to prevent an electrical or electronic device’s chassis from delivering an electrical shock. A long copper rod is driven into the ground outside of the building, and a wire connects the metal chassis to the rod which is at the approximate 0 V potential of the earth. The symbol for earth ground is shown in Figure 2.

Ground Details

Consider the following two details about ground. First, ground is not exactly 0 V. And second, two physically different ground points will not be at the same voltage potential.

Ground Loop

By definition, current will flow in an electrical conductor connected to a difference in voltage potential between two points. Because two physically different ground points are not at the same potential, current will flow through an electrical conductor connected between those two points. This is a ground loop.

Notice this current flowing between these two different ground points is not related to or correlated to any electronic data or message signal. This is noise or garbage that will interfere and distort any information contained in the electronic system.

Note: While “noise” can be added to systems on occasion, it is specifically controlled and the exact quantity is regulated.

Example

Given: A ground loop producing 610 μV of ground noise. It’s a very small quantity. You have a 16-bit A/D converter with a 0- to 10-V input. The smallest voltage it can resolve is:

= 10 V/16 exp 2

= 10 V/65,536

= 152.5ìV

Note that the ground loop noise is four times greater than the actual data, so that A/D converter loses two bits of resolution, and it is now a 14-bit converter.

Connect with Single-Ended/Unbalanced Amps

In Figure 3 the two grounds exist at different potentials, so some current will flow between the grounds. EE107-F3

This ground current has nothing to do with any signals being amplified, and it is noise decreasing the accuracy of the system. Figure 4 is a complete schematic.EE107-F4

Connect with Transformers

When connecting with transformers, keep the following in mind:

  • There is no ground connection, so there can be no Ground Loop.
  • Common-mode rejection of RF interference.
  • Signals are AC coupled, so of limited use for circuits with DC data such as accelerator focus and bend magnets (see Figure 5).EE107-F5

Connect with Differential Amps

Refer to Figure 6 for connecting two systems with differential amplifiers.

  • There is no ground connection, so there can be no Ground Loop.
  • Common-mode rejection of RF interference (see Figure 7).
  • Signals are DC coupled, so this is the perfect solution for circuits with DC data.EE107-F6EE107-F7

—Dennis Hoffman

Note: This article first appeared in audioXpress  (June 2011). It is from a class that Dennis Hoffman teaches at the SLAC National Accelerator Laboratory (Menlo Park, CA). Like Circuit Cellar, audioXpress is Elektor International Media Publication.

DIY Single-Board Computers

Countless technological innovations have certainly made the earliest personal  computers long obsolete. As Circuit Cellar contributors Oscar Vermeulen and Andrew Lynch note:  “Today there is no sensible use for an 8-bit, 64-KB computer with less processing power than a mobile phone. “

Nonetheless, there exists a “retrocomputing”  subculture that resurrects older computer hardware and software in DIY projects. It may be sentimental, but it can also be instructive.

In their two-part series beginning in July in Circuit Cellar, Vermeulen and Lynch focus on that strain of retrocomputing that involves designing and building your own computer system from a “bag of chips” and a circuit board.

Part 1 describes a simple single-board CP/M design that uses just one high-capacity RAM chip and is compatible with a serial or PC terminal.

Here is a homebrew N8VEM system with a single-board computer (SBC) and disk/IDE card plugged into the ECB backplane.

“It is easy to create a functional computer on a little circuit board—considering all the information now available on the Internet,” Vermeulen and Lynch say in Part 1.  “These retro machines may not have much practical use, but the learning experience can be tremendously valuable.”

Some “homebrewed” computer creations  can be “stunningly exotic,” according to Vermeulen and Lynch, but most people build simple machines.

“They use a CPU and add RAM, ROM, a serial port, and maybe an IDE interface for mass storage. And most hobbyists run either BASIC (e.g., the 1980s home computers) or use a “vintage” OS such as CP/M.

“Running CP/M, in fact, is a nice target to work toward. A lot of good software ensures your homebrew computer can do something interesting once it is built. As the predecessor of MS-DOS, CP/M also provides a familiar command-line interface. And it is simple. A few days of study are enough to port it to your circuit board.”

But some Circuit Cellar readers may want more from a retrocomputing experience than a one-off project.  In that case, there are online resources that can help, according to the authors.

“Working on your own, it can become progressively more difficult to take the next steps (i.e., building graphics subsystems or using exotic processors) or to add state-of-the-art microcontrollers to create ‘Frankenstein’ systems (i.e., blends of old and new technology that can do something useful, such as automate your home).”

Part 1 of their article introduces a solid online resource for taking retrocomputing to the next level–the N8VEM Google group, which provides a single-board CP/M design meant to engage others.

This is the N8VEM in its $20 stand-alone incarnation.

“N8VEM is not about soldering kits. It is about joining in, trying new things, and picking up skills along the way. These skills range from reading schematics to debugging a computer card that does not operate as intended. The learning curve may be steep at times, but, because the N8VEM mail group is very active, expert help is available if or when you get stuck….

“As the novelty of designing a simple single-board computer (SBC) wears off, you may prefer to focus your energy on exploring graphics systems or ways to hook up 8-bit machines on the Internet. Or, you may want to jump into systems software development and share your experiences with a few hundred others.

“Retrocomputing is not always backward-facing. Making  ‘Frankenstein’ systems by adding modern Parallax Propeller chips or FPGAs to old hardware is a nice way to gain experience in modern digital electronics, too.”

For more, check out the July issue of Circuit Cellar for Part 1 of their series. In Part 2, scheduled for publication in August,  the authors provide a technical look at the N8VEM’s logic design. It also provides a starting point for anyone interested in exploring the N8VEM’s system software and expansion hardware, according to Vermeulen and Lynch.

 

 

ALTspace – Cubes, Shame and Art

ALTSpace is a Community Art Workshop in Seattle. Creative people of all kinds share this spacious workshop, teaching, experimenting, making and learning. Members can spend time bouncing ideas off one another, hold or attend classes, work away from home and have the space to get even large projects done.

Location 2318 E. Cherry Street, Seattle, WA
Members 37
Website airlighttimespace.org

ALTspace hackerspace, Seattle

Co-founder Mike tells us about his space:
Tell us about your meeting space!

We have a total of about 2800 sq ft. We have two garage spaces for industrial machines, loud and dirty operations. (about 700 sq ft total) The rest of the space is for personal workspaces and public areas for working, meeting, hanging out. We have 2 showers, 2 bathrooms, a kitchen, a laundry room and an outdoor patio.

What tools do you have in your space? (Soldering stations? Oscilloscopes? 3-D printers?)

Full list of ALTspace’s tools & equipment.

Are there any tools your group really wants or needs?

A laser cutter would be our next purchase.

Does your group work with embedded tech (Arduino, Raspberry Pi, embedded security, MCU-based designs, etc.)?

Yes, we do quite a bit of electronics. One of our more well known projects, the Groovik’s Cube (A 30ft playable Rubik’s Cube) is an arduino driven project.

Can you tell us about some of your group’s recent tech projects?

Groovik’s Cube:

ALTspace's Groovik's CubeWe first built the cube as an art project for Burning Man 2009 and we’ve since been working hard to try and bring this project to the general public. We’ve been collaborating with the Science Center since summer ’10 and we’ve been doing a number of refurbishments including a brand new light-weight aluminum structure to create a neater look suitable for an indoor museum environment.

Groovik’s cube is a fully playable, LED driven Rubik’s cube, hung from the ceiling, corner down. (the motion is of course simulated, not mechanical, i.e. the colors move around, not the structure itself). It can be played and solved by the visitors. A particularly interesting feature is that we have split the controls into 3 stations placed around the cube, each allowing only one axis of rotation. This means 3 people have to collaborate together to solve it. The stations are ~30-50 ft apart from each other. This makes the puzzle considerably harder with a current record solution time of 50 minutes (achieved on Friday night @ Burning Man 09). It also turns a very introverted game into a collaborative challenge which is fun to watch. Imagine people shouting instructions to each other and running around checking on the state of the cube from different angles.

Temple of Shame:

ALTspace's Temple of Shame

by Alissa Mortenson, Nebunele Theatre, The Temple of Shame was a 6ft wide, 18ft tall wooden Temple dedicated to the collection of shame from the participants of Black Rock City. The temple was ceremonially burned on the last night of the festival to symbolically release all the shame collected.

From shameproject.org: “The experience of shame is part of our shared humanity, yet paradoxically, the times when we are ashamed are the times when we feel most alone. But within shame lies a capacity for human connection. The Shame Bearers seek to explore this emotion as a powerful medium for reaching a state of shared vulnerability. In order to make connection –the core human desire– we must believe that we are enough, that we are worthy of love and acceptance. In our vulnerability and our recognition of our mutual imperfections, we can find worthiness and connection. That is the power of this project.”

What’s the craziest project your group or group members have completed?

Groovik’s cube for sure.

Do you have any events or initiatives you’d like to tell us about? Where can we learn more about it?

Indeed: http://lsc.org/grooviks. We’re trying to raise funding for a new Groovik’s cube that will travel the World for 7 years together with Liberty Science Center and Erno Rubik!

What would you like to say to fellow hackers out there?

Hack more! Not satified with availability of hackerspaces near you ? Start one! It’s easier than you think and people come out of the woodwork to come and help and donate time and tools.

ALTspace’s tools & equipment:

Metal:

  • 2HP Metal Mill & Lathe
  • Lincoln 220 MIG Welder (up to 1/4″ steel)
  • TIG 200Amp DC/AC (i.e. Steel, Aluminum & other non-ferrous)
  • Plasma Torch (Up to 1″ steel or aluminum)
  • Stick Welder
  • Metal Grinding wheels, belt sanders
  • 4×6 Metal Bandsaw
  • Deburring wheel and 2 buffers
  • Wire bender
  • Abrasive metal chop saw

Machine Shop (Wood):

  • 3/4HP Table saw
  • Router table & Hand Router
  • Various Sanders (Orbital & Belt)
  • Miter Chop saw

Other Machine Shop amenities:

  • 90 PSI Compressor
  • 3/4HP 1/2″ Shank Drill press
  • Hand drills, Sander
  • 110V/230V Power (50A)

Glass:

  • Glass fusing/slumping/casting kiln, up to 1600 deg F

Jewelery setup:

  • Small Propane/Oxygen torch for soldering/annealing
  • Flexshaft Rotary grinder
  • Rolling Mill
  • Disc Die Cutter & Hemisphere punch

Electronics benches:

  • Maker bot
  • Soldering station with fume extractor and static pad
  • Multimeter
  • 100 Mhz Oscilloscope (Techronix)
  • Basic tools (snippers, strippers, screwdrivers, etc)
  • Variable voltage / current power supply
  • Stock of common components
  • Anti-static worktop

Sewing Area:

  • Pfaff industrial sewing machine
  • Janome domestic sewing machine
  • Hoseki HK757G is a 5-thread industrial serger
  • White domestic 4-thread serger
  • irons, cork-topped layout table, digitizing table, pattern plotter
  • Janome Computerized domestic sewing machine
  • Rowenta domestic iron
  • Sleeve board
  • Tailor’s ham
  • Pattern Drafting Rulers and curves
  • Costuming books

Read more about ALTspace’s Groovik’s Cube project on indiegogo or on Mike’s website, or about The Shame Project on shameproject.org!

You can read about more of ALTspace’s projects on their art page.

Show us your hackerspace! Tell us about your group! Where does your group design, hack, create, program, debug, and innovate? Do you work in a 20′ × 20′ space in an old warehouse? Do you share a small space in a university lab? Do you meet a local coffee shop or bar? What sort of electronics projects do you work on? Submit your hackerspace and we might feature you on our website!

Free Raspberry Pi Poster

The Raspberry Pi is a computer with no casing, no keyboard, no hard disk and no screen. Despite all that, it’s taking the world by storm!

Get your free Raspberry Pi poster now, courtesy of Elektor, RS Components, and CC! Go ahead: download, print, and then enjoy!

Free Raspberry Pi Poster

RASPBERRY PI ESSENTIALS

Model A has 256-MB RAM, one USB port, and no Ethernet port (network connection). Model B has 512-MB RAM, two USB ports, and an Ethernet port.

The Raspberry Pi Model B, revision 2 board:

  • Status led labels: top led has label “ACT” and bottom led has label “100”
  • Header P2 is not populated
  • The text underneath the Raspberry Pi logo reads: “(C) 2011,12”
  • The area next to the micro usb port has CE and FCC logos and the text “Made in China or UK” along the board edge.
  • There are two 2.9-mm holes in the PCB, which can be used as mounting holes.
  • P5 is a new GPIO header with four additional GPIO pins and four power pins. Also note that some pin and I2C port numbers of connector P1 have been modified between revisions!
  • Header P6 (left from the HDMI port) was added, short these two pins to reset the computer or wake it up when powered down with the “sudo halt” command.

The Raspberry Pi measures 85.60 mm × 56 mm × 21 mm, with a little overlap for the SD card and connectors which project over the edges. It weighs 45 g.

The SoC is a Broadcom BCM2835. This contains an ARM ARM1176JZFS, with floating point, running at 700 MHz, and a Videocore 4 GPU. The GPU is capable of BluRay quality playback, using H.264 at 40 Mbps. It has a fast 3D core which can be accessed using the supplied OpenGL ES2.0 and OpenVG libraries.

The Raspberry Pi is capable of using hardware acceleration for MPEG-2 and VC-1 playback, but you’ll need to buy license keys at the Raspberry Pi Store to unlock this functionality.

Which programming languages can you use? Python, C/C++, Perl, Java, PHP/MySQL, Scratch, and many more that can run under Linux.

TROUBLESHOOTING TIPS

If you’re getting a flashing red PWR LED or random restarts during the booting process, it’s likely that your PSU or USB cable has problems. The Raspberry Pi is pretty picky and requires a solid 5-V/1000-mA power supply. For other issues and more troubleshooting tips check out the extensive overview at the eLinux website

Circuitcellar.com is an Elektor International Media website.