Castellated pads

Without castellation service, done on purpose, on the typical Chinese PCB fab. [They seem to have ran out of ink on the silk screen too]

The through hole metalization is ripped apart at the time of the cut, so no electrical connection between the layers. The top and bottom metals are a bit shred and require a bit of filing to remove sharp corners. In short, quite unusable as castellation.



Fixing a broken scroll switch


A while ago I felt I needed to upgrade my work mouse to a higher resolution one, since I am mousing all around doing designs across 3 screens. In a purchase of impulse, I ended up getting a wireless one for a good price, the 4000dpi Mpow Dragon Slayer gaming mouse. I was happy with it for the first 2 months: 2-3 weeks of life at max resolution using rechargeable batteries without lights and an excellent match for my hand. Then the scroll started working improperly, it would change direction every few steps.

Fixing it

I thought the problem was not mechanical – bad contact, but since I did not have a spare scroll switch anyway nor time to invest in looking for a replacement…i thought i could try an electronic fix: de-bouncing the switch, which I saw no trace of being implemented on the PCB in a brief search. Cheaper de-bouncing is normally done in firmware, without passives, however if insufficient, I can compensate in hardware.

Here is the guilty switch, the one with the red part

DSC_6580The solution: add 2 1nF capacitors across the switches. I figured this would give a good de-bounce time with what looks like internal pull up resistors (~10…100KΩ) from the microcontroller.

DSC_6581And the terrible soldering job

DSC_6581-2Then I put it back together


DSC_6586Of course, opening it meant removing the feet, which don’t stick back properly



All done, the rodent is happily and properly working. Time will tell if this will last long enough, I will update if it breaks again. I hope the engineers at Mpow can see this and fix this really great mouse. Also a more “business” model would be great. The fact that the problem shows up so soon and for so many people tells me it is a software problem – not enough debouching. It only works while the switch is perfect. I have used plenty of mice so far and never found this to be an issue ever, even for much cheaper products.

Cheap China

[This article is alive and being updated with things that I use].

This is a summary about my experience with cheap electronic modules from China. I have used quite a few throughout the years, so there will not be any long video explanation, but more of a summary. The article is a living creature, with new updates as I test more stuff.

Why buy this stuff?

It makes sense for large distributors to sell you parts at exponentially higher markup when bought in smaller quantities, since it takes comparable effort to collect, package and send you 1 or 100. But the home user is interested in small quantity and most of the time using things in a typical diy recipe. This makes a ready made module carrying, for example, a real time clock chip along with its passives and backup battery a lot more attractive than just a bare chip. Since these modules are made of components quite close to the factories, in Asia, and sold avoiding a lot of the middle-men, it makes sense they would be cheaper than a 1-off component from a distributor. However, the ingredients used are not really top notch.

Some general observation first

These modules are cheap, generally everything is under 20ish EUR, which is the mark for paying VAT in the EU, varying slightly by country. This tax usually attracts another fixed import processing fee which raises the price significantly. Unless you are into high quantity, it makes more sense to buy items over this threshold locally.

The most important thing to understand is that these things are mostly provided ‘as is’ with no guarantees, no matter what ebay/other website will try to convince you, because…

“It works” does not mean what you think it means. I have learned this while discussing LEDs with a distributor: it works means there is light coming out of the LED, that is it. Big companies will count LED lifetime until it drops to about 70% of initial brightness. Generally speaking, “it works” means the thing is doing something somewhat related to what it should do, with no guarantee of any performance or operating parameters. 

In general, you should assume that the parts on the modules might be fab rejects, clones or even something totally different pretending to be the real thing. Words like “genuine” or “original” are thrown in the tile to tell you they mean business.

With such a low value of the items, there’s no surprise that even though the seller would accept a return, paying for the return shipping is a no go. And they know that.

When you buy a lot of X quantity of parts, there are some that are crappy and even dead on arrival. It happened to me buying the NRF24L01+ modules, DC/DC converters, PIR sensors, even headers. I suppose they might do some testing on the 1 PCS sales, not on the lots.

Quality and functionality of some module will decrease over time and is not consistent among suppliers, as they find more ways to cut cost or make a clone of a clone of a clone, see the NRF24L01 below. This is the reason why I am not linking to places of purchase, you will not get the same thing anyway.

However, things are not all bad and these modules are worth it for some application. Think for example the NRF24L01, you probably don’t care that it is not compatible with genuine ones, and I don’t care that 1-2 of the 10 are not working, since I can buy 20 for the price I pay for 1 at a distributor. And hopefully, we will both never find out they break any radio compliance. But, I would not use them if I were to build something and sell it.

These types of devices are great for hobby and learning, especially the troubleshooting part. Or sometimes just exploring and getting to know the feeling of a device. So, if you proceed with the right expectations, good things can happen and great projects can come to life.

Here are the devices I have experimented with, but don’t take this information for granted. There are numerous suppliers and very high variability with all modules, not to mention some room for user error.


ESP8266. This is an absolutely great device and without access to a real good supply of these modules it is hard to say if the quality problem is with ESP8266 IC itself or the modules are  just using bad parts. The 1 of the 2 modules i got first from electrodragon is still working fine in the LED logger. But, overall 2 others have died, both coming from ebay. Another thing I have noticed is that the devices, even though specified up to 1.8V and with good supply and decoupling capacitors, seem to operate only down to about 2.6V.


NRF24L01 – 2 black ones DOA got while working on the Stockie project. 2 more died during experimenting from a batch of 10, without being stressed in some way. Another batch of 10 had 1 DOA. They are partially incompatible with genuine chips or “real” copies like the RFM75. But things get really bad after a while as they are trying to make them even cheaper than they are. A green version exists with an incompatible pinout which I did not test because of this. The high power version used as a central node coupled with low power versions on other nodes can give you quite some range.


Step up/down DC/DC converter, lot of 5, look at the great soldering job. The IC is far off the PCB, with only a bit of solder at the end of the metal tab. They are nowhere near capable of what they promise, de-rate 2-3X for continuous operation because of bad soldering, under performing IC, no heatsink and high ESR caps.


3mm LEDS: quite a bunch of them. Very inconsistent in brightness at the same current. Quite a few of them dead, maybe 3-5%, so I would not throw this in a project without giving it a try. A couple of them they died without any stress in some more long term assemblies. Stay away from them if you want to use them in anything more permanent, I know I do.


Bad led strips, bright and nice warm light, but getting dim fast as tested with the LED logger. I use these in a wardrobe, so no problem with lifetime there, as they run only minutes per day.


Ribbon cable that is so stinking of plastic smell even after letting it “out to dry in the sun” for a month. No picture,  i threw the thing away.


These breadboards are so terrible i threw them away. They are crooked and rusty. Nowhere near the quality of a regular breadboard.


These breadboards are OK, but quite small.


Ramps 1.4. Thought getting everything for a driver is cheaper separately but this thing came with such bad soldering I had to give up on it. There is not much on the board that could not function, just that all the connectors on the back were poorly soldered at an angle.


Component tester. The original one is an absolutely great device and was on my to build list for a long time, however not of relevant priority. The version i got is much nicer, as it comes with a graphic LCD that is more intuitive to use. Precision is not that great, judging from comparison with the multimeter, but that is not what I am looking for. It is good to know some simple things, like if those cheap 3mm LEDs are DOA or not or making sure you don’t have a old and dried capacitor. SMD component testing is rather impossible by placing the part on the board. Recommend it only as an aid to a good multimeter.


1.44” or 2.2” IL9341 LCDs use a controller chip for which you can find a driver on many platforms. Pretty bad in terms of colours and one of them fell apart, even though it is still working. The headers are compatible across sizes and the big ones support an awkwardly placed SD card slot on them, but I never used it. They are the best thing to get if you need a cheap colour LCD.



WS2812 LEDs are a pleasant surprise, as my LED logger is showing, they are good for long term lighting. However, they do come with some limits, as the strip copper is highly inadequate for carrying all the current with LEDs at max. The data input pint is also very sensitive, I have managed to break quire a few. I am using them on the kitchen counter along with a motion sensor and that is pretty much the only light i normally use. Being RGB LEDs, they increase the “saturation of vegetables”.


WS2812 ring I got for an indicator, which was fine. However I tried to use one for lighting and they are nowhere near capable of dissipating the heat of all LEDs at max brightness constantly.


RFM69 – at the moment it costs about as much as it does at distributors, if I purchase 25 minimum. There is clear difference in components and the ebay one appears to be soldered manually and poorly. I suspect they are factory rejects manually fixed. My sensors website folks seem to use them without issues and the one I got works so far. However, I will continue to purchase them through regular distributors.


Voltmeters – the ones with 3 wires are great, you can even hack the micro on them. Don’t know about long term life or stability. 2 wire ones I have not tested, but I suspect they are more limiting.


Buzzers – waaaaaaaaaaaaaay quieter than the same thing from a distributor. [If CAPS says I am SHOUTING, what do I use to talk quieter?]


Terminal blocks – at quantities of 10s to 100 similar to distributor price, but the ebay ones stink.


Headers and connectors - cheaper than distributors, specially in small quantities. Some stink, some don’t. The gold coating is almost missing and they are more prone to oxidation. Avoid in things that you would care to work over long time, I suspect they will rust.


Jumper wires. I have talked about this one before.


FT232 adapters. I guess you know how these work out. Cannot say why, but I prefer the CP2102 modules below.


CP2012 USB-serial adapters. Clones, all with same serial number – a pain to manage multiple in various USB ports. Occasionally lose connection, but SW like YAT reconnect automatically. Edit: apparently the serial number can be changed, but I have not tried it.


Touch sensor – not low power, but ok. Seems to work, no long term testing. Given the application, there should be a jumper to disconnect the LED, as it is burning more power than the chip. Thought it can work as sit sensor, while experimenting for Sit.Up, but the auto calibration means it does not detect a touch after a few seconds.


Micro USB breakout – no issues, but they could have used thicker lines for power. A version with integrated ESD on the data lines would be a lot better.


Step UP DC/DC converter Noisy and pretty incapable of operating at the specified power. Use 2-3X derating.


USB battery charger – no issues so far.


QFN/TQFP to DIP adapter – smart because it lets you add a capacitor or pull down resistor to every pin. Not great, since the pads are too wide and solder bridges are hard to avoid. Don’t forget to connect the ground plane to the ground separately.


PIR sensors – have quite a few large ones operate for a few years. As with other packs, from a pack of 10, 1 was DOA, one very insensitive. Small ones seem to do fine as well, but are less sensitive and you cannot adjust the sensitivity or time.


CSR8645 bluetooth module. Overheating from start, despite proper supply. Died in less than 1h.


Bluetooth device for my blue panda. Died after some 10s of hours of usage over the course of a couple of years.


HC-SR04 – ultrasonic sensor. Works as described, but only briefly tested on the Sit.Up project.


US-100 sonar, smarter than the HC-SR04 and can operate at lower voltage. No long term testing, just brief playing with Sit.UP!


Nokia LCD – refurbished parts from old phones, mine have bad contrast requiring adjustment, but great LCD for some LOW power displays. More flexible than the typical 16×2 LCDs.


Vibrator motor – used in Sit.Up. One of 5 DOA and pretty weak compared to what is found in modern smartphones.


25 EURO oscilloscope. Just amazing what you can get in terms of oscilloscope for such a low price. I got it out of curiosity, it is pretty impractical, but it is a lot better than no oscilloscope for a beginner.