Free PCB Sunday: Pick your PCB

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We go through a lot of prototype PCBs, and end up with lots of extras that we’ll never use. Every Sunday we give away a few PCBs from one of our past or future projects, or a related prototype. Our PCBs are made through Seeed Studio’s Fusion board service. This week two random commenters will get a coupon code for the free PCB drawer tomorrow morning. Pick your own PCB. You get unlimited free PCBs now – finish one and we’ll send you another! Don’t forget there’s free PCBs three times every week:

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App note: Introduction to schottky rectifiers

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App note(PDF) on schottky rectifiers from Microsemi.

Schottky rectifiers have been used for over 25 years in the power supply industry. The primary advantages are very low forward voltage drop and switching speed that approach zero time making them ideal for output stages. This latter feature has also stimulated their additional use in very high frequency applications including very low power involving signal and switching diode requirements of less than 100 picoseconds.

App note: What is a silicon transient voltage suppressor and how does it work

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A primer app note(PDF) on silicon transient voltage suppressors by Microsemi.

Silicon transient voltage suppressors (TVSs) are clamping devices that limit voltage spikes by low impedance avalanche breakdown of a rugged silicon pn jucntion. They are used to protect sensitive components from electrical overstress such as that caused by induced lightning, inductive load switching and electrostatic discharge.

Linux Foundation offers free online course


Jerry Cooperstein, PhD, Training Program Director at The Linux Foundation has announced the opening of their free online course, Introduction to Linux (Course number LFS101x).

The course is self-paced and should take between 40-60 hours to complete. We’d love to hear how you’re enjoying the course and we’d love to hear when you complete it! Just tweet us at @LF_Training using the hashtag #LinuxMOOC, or leave a comment on our Facebook or Google+ pages. Happy learning!

(The course is free to those wishing to audit the course or try for a certificate of achievement. If you want to earn a “Verified Certificate of Achievement” there is a $250 fee.)
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App note: Real-time versus equivalent-time sampling

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Real-time versus equivalent-time sampling (PDF!), an app note from Tek:

When a DSO uses equivalent-time sampling, it can acquire any signal up to the analog bandwidth of the scope regardless of the sample rate. In this mode, the scope gathers the necessary number of samples across several triggers. The input signal must be repetitive to generate the multiple triggers needed for equivalent-time sampling. In equivalent-time, a slower, lower-cost digitizer provides the same accuracy on repetitive waveforms as a higher cost DSO with a faster sampler. For example, the TDS 460 offers a 350 MHz bandwidth with only a 100 MS/s sampling rate on each of its four channels.
The TDS 400 and TDS 500 Series scopes use a common method called random equivalent-time sampling. Although these scopes acquire samples sequentially after each trigger, each acquisition starts at a different time with respect to the trigger. Figure 1 depicts how random equivalent-time sampling works.

App note: White LED driver with digital and PWM brightness control in 2mm x 2mm QFN package

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An application note from Texas Instruments, white LED driver with digital and PWM brightness control (PDF!):

With a 40-V rated integrated switch FET, the TPS61160/1 is a boost converter that drives LEDs in series. The boost converter runs at 600kHz fixed switching frequency to reduce output ripple, improve conversion efficiency, and allows for the use of small external components.
The default white LED current is set with the external sensor resistor Rset, and the feedback voltage is regulated to 200mV, as shown in the typical application. During the operation, the LED current can be controlled using the 1-wire digital interface ( Easyscale™ protocol) through the CTRL pin.

Random Saturday electronics blog

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Replacing a NIC with something hopefully high quality from Intel. Noticed that Intel uses a healthy mix of 0402, 0603, and 0805 components. Especially capacitors. Not sure if this is due to cost vs capacity, or if smaller, harder to place components are used sparingly as needed. From experience typical caps get cheaper as they get smaller, except for very large values like 10uf ceramics.

I need this card and am reticent to pull it apart to measure the values. Its really tempting though. Any thoughts?

BTW discovered WordPress apparently was installed on my Nexus 5, thus ushering the era of random China and workshop blogging. Hope you enjoyed it so far this week.

Mini line tracer

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Pinomelean wrote this instructable detailing the build of his analog line tracer robot driven by a dual op-amp chip:

It’s a simple line tracer, controlled by two op-amps. No microcontroller, no programming… simple analog circuitry.
I tried to make it as small as possible, using SMD components and tiny motors.
I’m very happy with the final result, the robot can follow 1-2cm wide black lines on white background, and is quite fast.
It can be made to follow white lines on black background by switching the position of a couple components.

Check out the video after the break.
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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:

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Week in (p)review August 01, 2014

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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
  • Free PCBs via Twitter on Tuesday
  • Weekly roundup and preview every Friday

Site up, site down, fingers pointing everywhere…

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Over the past week things have been getting really slow and buggy around here. I reinstalled WordPress a bunch of times to get rid of the slow and timeout comment bug, but last night someone said it’s back.

A system admin has been working on it for the past few days. We found some corrupt database tables. That was causing down time when we do database backup and optimizations. The backup processes and Jungle Disk process would hit that spot too and take the server down.

We ran a disk check. SMART data shows the disk is ok, but pre-failure. A disk scan shows no corrupt blocks. That suggestes maybe the disk controller was bad. Just a few minutes ago our host Hetzner took the site offline and did a system check – no problems were found.

So… Now we’re left with a server going up and down about once every five minutes. Absolutely no concrete cause or solution in sight. Compound that with trying to troubleshoot over totally unbearable Chinese internet that now blocks foreign mail servers, as well as DP half the time, and we’re left with few good options.

My best guess is we will go offline for a while sometime today and transfer to a fully managed host on the US West Coast. We’re currently in a datacenter in Germany because of the strong privacy laws that protect system admins and users, but that’s of no use if I can’t admin the box from China.

SPI Transactions in Arduino

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Paul over at DorkbotPDX writes:

For the last several weeks, I’ve been working on SPI transactions for Arduino’s SPI library, to solve conflicts that sometimes occur between multiple SPI devices when using SPI from interrupts and/or different SPI settings.
To explain, a picture is worth 1000 works. In this screenshot, loop() repetitively sends 2 bytes, where green is its chip select and red is the SPI clock. Blue is the interrupt signal (rising edge) from a wireless module. In this test, the interrupt happens at just the worst moment, during the first byte while loop() is using the SPI bus!
Without transactions, the wireless lib interrupt would immediately assert (active low) the yellow chip select while the green is still active low, then begin sending its data with both devices listening!

Touring in Shenzhen video series from Limpkin

Touring factories in Shenzhen: Visiting an assembly line, Seeedstudio and a CNC shop

Shenzhen is the geek’s paradise and can be described as an awesome concentration of very different companies, all within an hour cab ride from your hotel. If you ever go there, I highly recommend you to have a look at Ian’s article  to get practical informations. Shenzhen is located in the south of China, right next to the border with Hong Kong. I therefore decided to spend my first day in this former British colony to buy myself a nice camera to bring back cool videos of my adventures.

More video below the break.

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SmartMatrix Shield Pro

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EmbeddedCreations writes:

I’ve been working on a new version of the SmartMatrix Shield, not meant to replace it, but to be an option for those that want to maximize the capabilities of the Teensy, while connecting to a matrix display. Let’s call it the SmartMatrix Shield Pro. This board will have the advantage of pinout/functionality, but the original shield will have advantages of size, cost, and ease of assembly.

Via the forum.

Digitally controlled bench PSU

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Bertho posted a digitally controlled PSU design in the forum. He writes:

The design is for 0…30V and 0…3A (90W) controllable at ~1mV and ~0.1mA steps. The actual accuracy is still out for testing and I assume that noise and non-linearity will be a factor to look at when time comes. The basic design allows for 0…42V (max 45V) and (at least) 0…4A, but then all the components should be re-calculated to match such setup. Also, some components need to be voltage matched for a higher input voltage.
The design is a dual control-loop where the first stage is a switching PSU which is fed back to assure a 2.5V drop over the secondary analog control stage. The secondary stage is also responsible for the current limiter. The idea here is to reduce the power loss in the BJT (Q4) in the analog stage.

Tripping to South China Market in a bread van

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The entire Pearl River Delta area of China is a manufacturing powerhouse. Huaqiangbei, the famous giant electronics market, is just a tiny facet of a huge industrial ecosystem. About 30 minutes north of Shenzhen there’s a giant market the size of a town that supplies not just electronics, but chemicals, materials, tools, machines, and, of course, furs and leather.

South China Market is a planned development resembling a covered lumberyard spanning several square kilometers. Its frikin’ huge, but also eerily empty. They built it up, but its either not been successful or is still filling out. This street is almost exclusively ABS plastic bead vendors, with a few colorant shops interspersed.

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We met up with Zach Hoeken on a rainy afternoon to check out the market. None of us had been there before, but everyone had read Akiba’s account from his trip there last year.

Zach’s new “mian bao che” bread van had a dead battery. Bread vans are the Volkswagon bus of China, a bare bones, no frills utility vehicle. We jump started that death trap from an electric scooter and hit the road. Only in Shenzhen!

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The market is divided roughly into quadrants. Our first stop is the metal and materials market. Check out the plastic water bottles, hand labeled in Chinese, holding various chemicals and food additives. We feel really unprepared as there’s gotta be some great stuff to play with, but we didn’t do enough research to know what.

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55 gallon drums of chemicals line the street. The bags are mostly ABS plastics pellets, some of the barrels are labeled glycerin.

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Nothing but grinding bits and grinding wheels here.

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A rosin supplier with dozens of grades in different qualities and colors. Your flux could be based on some of this stock.

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A bag making shop. Spools of plastic tube, printed or clear, are cut and sealed into bags. Curiously enough, we spot a factory making the tube stock from raw plastic beads a few days later.

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Bag shop? Check. Tape shop? Yeah, right next door. This is a custom tape cutting machine. Long rolls of tape are loaded and cut to various widths by what seems to be a computer controlled skill saw.

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Long rolls of tape stock, ready to be cut to width.

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Zach, co-founder of Maker Bot, checks out a 3D printer shop in an otherwise deserted floor of the electronics market building.

The electronics market was super weird. A brand new building, clean and stylish, but almost nothing inside. Floor 1 is about half full of quite modern electronics components and industrial control equipment. Floor 2-3 were mostly abandoned, and floor 4 had never been used.

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We call this the burner shop – get all your day-glow, reflective, sparkly Burning Man materials here.

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Laser cut patterns in fabric.

China is really laid back. There aren’t many places in the world where a couple foreigners can roll into a factory, have a poke around, and nobody even looks up.

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A very handsome Velcro square cutting machine.

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Wholesale wheelie bag frames. You know, the kind some douche is always fighting into a too-small overhead compartment on a plane. They gotta come from somewhere.

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Tea and tea supply wholesale. According to the shop girl, everything is an “investment piece” that will always go up in value. Sure.

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The fabric quadrant is surprising. Shops advertise sandwich. It turns out to be a layered fabric and not a tasty lunch, but the shop people never tire of foreigners asking for one with ham and cheese.

Several street are full of fur vendors, both surprising and slightly disturbing. Fake furs and real firs, mostly fox and rabbit.

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More furs. Bundles and bundles of them. We all leave slightly inclined to make custom tailored fir coats, pajamas, and pillow cases.

South China Market has been on my to-visit list for more than a year, and it was definitely past time to visit. We’re researching fun chemistry experiments (glow sticks, super balls, snakes), and will go back soon to source supplies.

If you’re only visiting Shenzhen for a little while though, it’s not worth the effort to go here. While it is huge, it was mostly empty during our visit and the electronics market is like a ghost town. If you’re seriously into ABS plastics, chemicals, or fabric you can probably find anything you want.

Next on our list: Shajing market. This is supposed to be a huge tools and equipment market with a fun toys you can’t find in the Huaqiangbei electronics market. We’re hunting for a small injection molding machine to use with the 50kg bag of ABS plastic pellets we bought at South China Market.

Wearable pupillometer could detect dangerous diabetic condition earlier

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Mang Ou-Yang and his team at National Chiao-Tung University have developed a wearable pupillometer. It could detect dangerous diabetic condition earlier:

Compared to the existing diagnostic techniques, the pupillometer is a more reliable, effective, portable and inexpensive solution for diagnosing diabetic autonomic neuropathy in its early stages,” said project leader Mang Ou-Yang, of National Chiao-Tung University.

Via Gizmag.

Arduino GSM home automation system

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Timofte Andrei wrote this instructable detailing the build of his Arduino home automation system:

For this project I’ve used:
1. An Arduino clone
2. SIM900 GSM SHIELD
3. Relay module
4. 2×16 LCD Display
5. DS18B20 temperature sensor
6. Push button
7. Some Dupont wires
8. A led module (this is optional, if you have a chinese relay module with built in LEDs)
9. Some nuts and bolts to mount everything in place
10. A wooden chopping board or other kind of wooden board for propper display of the components

Via Hacked Gadgets.