App Note: Designing a simple isolated flyback DC to DC converter

Here’s’ a video tutorial from Linear Technology describing how to design a simple flyback DC/DC converter. The video promotes the use of LT’s LT3573 IC, but it also provides information that could be applied to other designs as well.

Isolated power supplies are needed in a wide variety of applications. Galvanic isolation is achieved by isolating two or more circuits using a transformer or optocoupler, and is desirable for many reasons: safety, noise immunity, circuit protection, etc. Traditionally, isolated power supplies use an optocoupler to transfer regulation information across the isolation barrier.

Things in Shenzhen: Tailors in Louhu

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Besides hunting electronics, we always have clothes tailored in Shenzhen. The Louhu Commercial City is a mall right outside the boarder crossing. Its mostly knock off crap, but at the top there’s a huge fabric market and dozens of tailors. They do suits, but also anything you can imagine, and its way cheaper than the classic Hong Kong layover suit. Shirts run 125 rmb (20 bucks), pants 100, and jackets 400 rmb (65 bucks). You might think it isn’t for you, but you gotta try it. The group of MIT grad students here with Bunnie were hesitant, but one they took the dive everyone had something made. Look for an pic of Akiba @ FreakLabs’ fancy coat on Tue twitter feed next month.

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Out of Shenzhen: Sea of people at Louhu/Lo Wu

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Guide books warn that the boarder crossing from Hong Kong to Shenzhen at Louhu can be extremely busy. We’ve always sailed through in a couple minutes. Today, after leaving China immigration, we encountered this sea of people in the no mans land bridge to Hong Kong. Still only took about an hour to get through, amazing how efficient immigration is.

Out of Shenzhen: Nannie Sunday in Central

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Hong Kong nannies, mostly from the Philippines, have Sunday off. Thousands of nannies gather and setup camp along Central Hong Kong island. Its absolutely one of the coolest things to see on a Sunday afternoon, and a great chance to practice my 4 Pinyo vocabulary words – salamat, oo, hindi, and seget (spelled phonetically).

Out of Shenzhen: Central mid level escalators

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In my humble opinion the kilometer long central mid level escalators are the top attraction in Hong Kong. On the way out of Shenzhen we always check in and drop bags at Hong Kong city checking and then head up about half way to Taco Loco for some if the best carnitas tacos anywhere in the world. What else are you going to do when you don’t fly out until 2am. Yes this post is a little first person and violates our editorial guidelines :)

Embedded Projects Journal article on Bus Pirate

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For those readers fluent in German, fG draws your attention to an article discussing the Bus Pirate. To us it looks like they’re discussing using a BP to assist in reading an online banking card. The article is found on pages 16-25 of the Embedded Projects Journal. You can download the 36-page PDF of the December 2012 issue (in German) here.

Get your own assembled Bus Pirate for under $30, including world-wide shipping. Also available from our friendly distributors.

Via the contact form.

App Note: Differences between switch mode, linear, and pulse Li Ion battery chargers

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Here’s a tutorial from Maxim describing the differences between switch mode, linear, and pulse Li Ion battery chargers. Advantages and disadvantages of each are covered by the article.

There are three methods to charging Li+ batteries: switch-mode, linear and pulse. Each method has its advantages and disadvantages. Switch-mode charging minimizes power dissipation over a wide range of AC adapter voltages, but consume more board space and add complexity compared to linear and pulse charging. Linear chargers are small and great for noise sensitive equipment, but power dissipation is high. Pulse chargers are small and efficient, but require a current-limited AC adapter. Select the charging method based on the prioritization of cost, space and efficiency.

App Note: Reballing BGA devices tutorial

Here’s a video tutorial on how to reball BGA devices. First you’ll need to remove the IC, and clean up the leftover solder from the IC and the board. Next step is to place the ball grid template over the IC and add tiny solder pellets which when heated will adhere to the IC. Once this is complete you can place the BGA back on the board and solder it again.

Wireless Innovation Forum SDR design challenge

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The Wireless Innovation Forum has announced they are accepting proposals for entry into their SDR design challenge.

“Undergraduate and graduate students or teams of students, advised by a faculty member, are eligible and may propose and solve any problem related to SDR/CR/DSA. Senior capstone or graduate thesis projects, class projects, sponsored projects, and independent projects are all eligible and may have already begun before the proposal due date. At minimum each entry should include an implementation of a software-defined radio (SDR) link or receiver that can be demonstrated using available signals or using an experimental frequency allocation. Undergraduate and graduate students or teams of students, advised by a faculty member, are eligible and may propose and solve any problem related to SDR/CR/DSA. Senior capstone or graduate thesis projects, class projects, sponsored projects, and independent projects are all eligible and may have already begun before the proposal due date. At minimum each entry should include an implementation of a software-defined radio (SDR) link or receiver that can be demonstrated using available signals or using an experimental frequency allocation.”

Proposals are due February 8, 2013.

To obtain access to the Challenge entry form and learn more, visit the contest web page.

(Note that while this contest and related symposium are hosted in the United States, we do not see a limitation in their rules barring entries from eligible students outside the US.)

Free PCB coupon via Facebook to 2 random commenters

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Every Friday we give away some extra PCBs via Facebook. This post was announced on Facebook, and on Monday we’ll send coupon codes to two random commenters. More PCBs via Twitter on Tuesday and the blog every Sunday.

Don’t forget there’s free PCBs three times every week:

Continue reading “Free PCB coupon via Facebook to 2 random commenters”

Week in (p)review January 25, 2013

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Here’s a summary of major developments over the last week. Free PCB Friday is coming up soon.

Coming up:

  • Free PCBs via Facebook on Friday
  • App notes on the weekend
  • Free PCB Sunday
  • 3D model on Monday
  • Eagle parts and tips on Tuesday
  • Free PCBs via Twitter on Tuesday
  • A new tutorial on Wednesday
  • Workshop video on Thursday
  • Weekly roundup and preview every Friday

Raspberry Pi VPN

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The Hoz directs our attention to this Lifehacker article explaining how to setup the R-Pi as your own personal VPN. The project hardware requires only standard R-Pi peripherals, including keyboard, mouse, monitor, SD card and Ethernet connection. You’ll also need a free account with LogMeIn. (They point out that OpenVPN may be a good alternative to LogMeIn for those with a static IP or dynamic DNS service.) Privoxy is also used to enable secure web browsing.

Via Lifehacker.

555 based constant current lead-acid battery charger

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Kennith needed a 1A constant current lead-acid battery charger for his HAM radios. He augmented the 555 contest winning battery charger circuit by replacing the relay with an LM317 in constant current mode.

Since the SLAs are relatively small, and I only need them charged between radio outings, I opted to build a 1A constant current charger, based on the 555 Battery Charger which won first place in the 555 Design Contest Utility category. Using a 555 is a rather clever way to get two comparators and a Set-Reset latch in a single 8DIP package, which is needed for the high and low trip points. The major difference between my design and Mike’s is that instead of using a relay like him, I use an LM317 as a constant current source to limit my batteries charge rate.

High quality entropy source

Wardy decided to build a high quality random number generator. After searching the web he stumbled upon this project which uses a laser hitting sand in an hour-glass to generate the randomness. He upgraded the project a bit by adding a servo to reset the hour glass. He is currently recording a large number of samples to test out the randomness of it all.