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New Zealand's longest-running online daily news and commentary publication, now in its 25th year. The opinion pieces presented here are not purported to be fact but reasonable effort is made to ensure accuracy.

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Reverse engineering cheap Chinese electronics

29 Jan 2024

I spent a few hours yesterday connecting wires, batteries, PCBs and other assorted bits at the workshop.

It's crazy how making electronic devices has changed over the years and now it's easier than ever -- well "almost".

As I mentioned a few days ago, I'm in the process of creating several new pieces of "safety technology" for those who fly drones and RC models. I could have designed and built everything from scratch but that's a pretty time-consuming and complicated process so I decided to use as many pre-built modules as I could and yesterday was as frustrating as it was enjoyable because of this.

One of the key modules I'm using in these projects is a cool little circuit-board that handles the task of charging a lithium-ion battery and also boosting the voltage of that battery from a nominal 3.6V to the 5V needed to power other bits of the circuit.

Once upon a time this would have been a complex task on its own and would have required time, effort and expense to design, develop and implement this functionality at an individual component-level. Thanks to the wonders of AliExpress and a surfeit of suppliers flogging such boards, I was able to simply buy a solution off the shelf for a couple of bucks.

Well it's a solution that "should" have worked... but, as is so often the case, the devil is in the detail and AliExpress vendors seldom document their wares in a comprehensive or even useful way.

I took one of these little boards, connected it to a li-ion cell and checked that it was indeed producing the requisite 5 volts to power the rest of my circuitry.

Yes!

However, something strange was happening.

After 30 seconds of operation, the power went off.

Resetting the little circuit-board restored the power and so I carried on... for just 30 more seconds.

WTF?

Ah... there's a feature, undocumented by the vendor, that this little board has a load-detection function that automatically powers everything down it it senses that there's nothing connected to the output.

But there *was* something connected to the output -- so what's the guts?

After downloading the datasheet for the chip being used I discovered that there is a threshold of 45mA which must be drawn in order for the board to keep providing power beyond the 30-second mark.

Damn, my circuit is only drawing about 30mA so the little AliExpress board thinks nothing is connected and shuts down.

Fortunately, there was a very easy fix for this... I just added a 200 ohm resistor across the 5V output and that brought the total current draw beyond the trigger threshold so everything then worked as expected -- albeit at the cost of 125mW of power wasted heating up that resistor. Given that the battery has an 18WH capacity, that tiny amount of extra power draw won't be even remotely significant -- but it still grinds my gears a little.

And this speaks to the problem associated with poorly documented bits of electronics...

You can waste an inordinately large amount of time just trying to figure out how to properly use something, when there is no documentation.

For example... another pre-built electronic module I'm using has six buttons and the function of the buttons is documented in the finest "Chinglish". However, although they refer to buttons 1 through 6, there is no indication which of the buttons is which. No picture, no drawing... nothing! Only by quite a bit of trial and error was I able to decode this cryptic mess -- something made all the more difficult by the fact that the buttons change mode depending on previous button-presses.

Ugh!

After the last week or two I'm changing my perspective a little on using these super-cheap, off-the-shelf prebuilt modules.

Yes, they're a fantastic way to reduce the time and cost of building an electronic device but that has to be weighed against the frustration and effort sometimes required to reverse-engineer and document all the details needed to make them work.

In future, I'll be choosing my modules based more on the level of available documentation than on price or performance.

If these vendors realised the importance and the value of good documentation then perhaps they'd sell more stuff and could charge a higher price. Ah, but that's not the way AliExpress works is it?

You pays your money and takes your chances!

Finally, to follow-up on a previous purchase, I ordered some more of the rather nice teeshirts I got a while back. I ordered them last week and they've already arrived -- once again at a lower price than I can buy locally, even with AliExpress adding GST and the thousands of miles they were flown from the factory to my door.

At least teeshirts don't require much in the way of instructions or documentation :-)

Carpe Diem folks!

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