Taobao breakout boards are a mess part 2


Last week we struggled with mislabeled and faulty breakout boards from Taobao. Fortunately purchases from Shenzhen sellers usually arrive the next day, so we’ve already got a bunch of replacement boards to test.

HMC5883L/QMC5883 digital compass

Last week our HMC5883L breakout turned out to have a non-compatible QMC5883 chip. We need the genuine part to do a demo so we purchased four more from different suppliers. Each supplier confirmed that the breakout has an original HMC5883L, not the guochan (locally produced) QMC5883.

Of the four boards, only one has a genuine HMC5883L. The only seller with the original part actually offered the option of a guochan version for around 10RMB, or the original for around 40RMB. All the other breakouts came with a QMC5883 and cost around 10-15RMB. There are dozens of listings for this breakout on Taobao for around 10RMB, it’s safe to assume they’re all actually using a QMC5883.


One of the sellers of the QMC5883 boards strenuously argued that the part was real and drew a helpful circle on our photo pointing out the model number. We countered with a photo of the chip markings compared to an original. At this point someone higher in the support chain, probably the boss, confirmed that “everyone” switched to the cheaper Chinese chip a year ago, and that buyers all know this. Now we know too.

SHT21 temperature and pressure sensor


First, a correction from last week. We made a pretty basic mistake reading the SHT21 datasheet. The measurement resolution control of the configuration register is split into bits 7 and 0, not 7 and 6. After recognizing this the default value 0x3A is realistic.

Read correctly, bit 6 (0) correctly shows VDD > 2.25volts, the heater is disabled (bit 2=0), and OTP Reload is disabled (bit 1=1). Embarrassing, but an encouraging sign things are looking up.


That leaves the issue of the impossibly high and definitely incorrect humidity measurement. We purchased a replacement SHT21 from Youxin, the original vendor, and samples from two other Taobao sellers.

All three breakouts work as expected, but on closer examination the board on the far right is actually an HTU21, not a Sensirion SHT21. HTU21 is a drop in replacement for the SHT21, but much cheaper. An Sensirion original is around 30RMB ($5), while the HTU21 is just 10RMB (~$1.50). The seller marked it as an SHT21 original and charged the market rate for an original (~35RMB). An extraordinarily low price consistently means non-original parts, but unfortunately a reasonable market price isn’t a reliable indicator of genuine parts.

It’s probably not a scam

The confusion probably starts with first line support reps that don’t know what they’re selling. If it says HMC5883, it must be HMC5883, right? Another part is being an informed consumer. If the original goes for 40RMB, the 12RMB version is going to be a substitute. This is obvious now, but the sheer volume of mislabeled listings makes it really hard to get a handle on a reasonable market price.

Taobao offers a huge selection of inexpensive parts, and next day delivery is usually around $1. That’s really amazing! However, getting multiples of everything to ensure at least one is genuine probably costs more than buying from a western-facing supplier like Seeed Studio, SparkFun or Adafruit.

The K7TMG HF Morse code temperature beacon


AA7EE published a new build, a little temperature beacon:

This was a fun little project – and it gave me an idea for a future one. Sometimes, I find that the more complex undertakings, which require more planning, can get to the point that they “take me over” somewhat. At that point, for me, some of the fun starts getting squeezed out and that, of course, absolutely cannot be allowed to happen. This is the time when simple and fun projects save the day.

Check out the video after the break.

See the full post at Dave Richards AA7EE blog.

NickelBot – Laser controller


bdring made this laser controller for his wooden nickel engraver project and wrote a post on his blog detailing its assembly:

Here are some details on the custom laser controller I made for the NickelBot, wooden nickel engraving machine.
I want to use Grbl to control the machine. Grbl has support for lasers that allows better power control during the engrave. It also has the Core XY support I need for the H-bot mechanism it uses. The only feature I needed that it did not have is a hobby servo output.

More details at Buildlog.Net blog.

App note: High-speed lithium-ion battery charger


C8051F300 implementation of Li-Ion battery charger from Silicon Labs. Link here (PDF)

Driven by the need for untethered mobility and ease of use, many systems rely on rechargeable batteries as their primary power source. The battery charger is typically implemented using a fixedfunction IC to control the charging current/voltage profile.

The C8051F300 family provides a flexible alternative to fixed-function linear battery chargers. This note discusses how to use the C8051F300 device in Li-Ion battery charger applications. The Li-Ion charging algorithms can be easily adapted to other battery chemistries.

AtPack: Atmel Pack parser, visualizer and fuse calculator



AtPack – Atmel Pack parser, visualizer and fuse calculator from Vagrearg:

Looking for an up-to-date fuse-calculator for the Atmel(*) AVR chips has been something of a long search. There are several online versions, but they have not been updated to the new chips (like the ATmega328PB).
When you have got an itch, you simply scratch it… Don’t you?
Well, I did, and it resulted in an analysis of the Atmel Pack format, which can be freely downloaded under an Apache 2.0 license. The AtPacks contain a master XML file with device lists and links to each device’s XML file, which in turn describes the entire chip. The format is not that hard to understand and can be easily mangled into something useful. Then, some crude jQuery hacking and many hours later… you know how that works.

Code is at GitHub and there is an online version.

Via Vagrearg.

Breakout boards from Taobao are a mess


For the last few days I’ve been playing with breakout boards purchased from Taobao. So far it’s been a nightmare.

GY-271 is advertised as a Honeywell HMC5883L 3 axis digital compass. A Bus Pirate address search turned up 0x1A and 0x1B, instead of the HMC5883L’s 0x3C and 0x3D. The chip is actually a “Q”MC5883L, a Chinese-made digital compass with similar features that is not register compatible.

The datasheet for the QMC5883L shows the chip markings as “DA5833”. These markings are visible in nearly every Taobao listing claiming to be a HMC5883L breakout boards. Honeywell’s datasheet doesn’t include chip markings, shame on them.

GY-273 is another HMC5883L breakout board all over Taobao. About half of these are clearly the “Q” type chip. The other half show the Honeywell chip, at least in the photo. After talking with a quasi-trusted vendor I ordered what are supposed to be actual HMC5883L breakouts.

GY-213 is a breakout board sold with a variety of temperature and humidity sensors, including SI701, SHT21, etc. The same color/size/pinout/layout PCB is available from tons of Taobao shops. I ordered a SHT21 version from Youxin, a trusted supplier. The chip appears to be genuine, not the Chinese-made HTU21D, but it seems to be defective in at least two ways.


Reading out the configuration register shows 0x3A=00111010, but the power up default should be 000xxx01. At power up the on-chip heater is enabled, which is used for testing and diagnosis. “OTP Reload” is enabled, which is specifically “not recommended for use” by the datasheet.

After setting the correct configuration it was time for further disappointment. Humidity measurement is always around 0xF66A. 114.3% humidity seems unrealistic, even for Shenzhen in the spring.

Lipo charge/boost/protect board in 18650 cell holder format


Peter6960 published a new build:

So couple months ago, GreatScott made a video where he designed a circuit. Nothing too innovative, just the same TP4056 charger the MT3608 Boost combined on one PCB. He did add a Lipo protection circuit though, initially using the same DW01. But then, the Aha moment from this video, he found a footprint compatible IC the FS312F-G – which is set at 2.9v! Way healthier for your cell’s longevity!
First of all I had to redraw all his work in Eagle (As I wont be using a cloud based service like EasyEDA for obvious reasons) and then order the PCBs. I added two boost circuits since I had the board space, as I can imagine needing dual voltages at some point (for example if that reverse LCD needed 12v and the Pi needed 5v – i could run both off one board.

Project info at

App note: Preventing LED failures caused by corrosive material


Chemical compatibility of LEDs application note from OSRAM. Link here (PDF)

The performance and stability of light emitting diodes (LEDs) may be influenced by various chemical incompatibilities arising from chemicals and materials used, amongst other things, in luminaire construction, or by gases in the proximate environment of LEDs during field operation. Nevertheless, LEDs have to fulfill a wide range of customer needs and requirements in indoor and outdoor applications.

This application note provides information about the chemical compatibility of certain substances with LEDs, particularly with regard to some of their basic components. In this context, the main mechanisms of chemical incompatibility are illustrated using examples of blue and white LEDs.