Tuesday, October 10, 2017

Charge a smartphone battery without the phone nor the charger

I shortly dipped my phone in sea water and the charging/battery control circuitry and micro USB plug got oxidized beyond repair (salt is really terrible). I could have saved it at the time if I had a chance to open it and carefully rinse the electronics with non-salted water immediately, but I miss my tools on holidays... While waiting for a replacement part to arrive, I had to recharge the battery the DIY way.

Recharge a smartphone battery with a super cheap lithium ion recharging module and pogo pins.
The short pieces of thick copper wires (in blue) are compulsory to present the retractable pins correctly
They are maintained in perfect contact with clamps on a soft silicon mat.

Saturday, July 15, 2017

Using PCB rivets vias for homemade double sided PCB

You may remember in a former article the super tiny rivets I bought for double sided prototyped printed circuit boards (these but check those, they are way cheaper!). I realize that I never documented how I used them. So here it is.

The "raison d'être" of these costly rivets is specifically to help doing the vias that route the signals from one side to the other side of the board. The industry does plated holes with a chemical process that deposits a layer of conductive metal on the inside walls. It both conducts the signal but it also really helps making the board sturdier, as the copper rings (well square, here), are bonded together. Without it, the risk to tear apart one of them is much more important. Actually, a few makers do it also but it is both difficult, lengthy, messy and specially risky with a lot of nasty chemicals... not for me since I mill my PCB ;)

So in general, making double sided PCBs at home means there is no such plated holes. So we usually solder a thin wire through the hole on both sides. It is time consuming and it stresses the copper pads a lot, especially when the damn wire falls down when both sides melt again when you just want to solder the other side ;)

Top and bottom layers: making vias by means of PCB rivets on a double-sided milled PCB.
The milling job is quite bad here: the traces were not cut properly on the top layer (left side, check why here),
and the layers were mis-aligned after the board was flipped over to mill the top side... I need more practice.
Also, there are better and expensive tools to fix the rivets, but this prototype worked fine in the end anyway ;)
Now, rivets still help to make more robust single sided PCBs, most notably for the connector holes that will be subject to mechanical stress. Rivets will protect and keep the small copper "rings" tightly bounded to the PCB support material, so they will be less likely torn away.

Most notably, dirt cheap bakelite boards give no second chance in this respect, while fiberglass (FR4) endure more abuse and re-soldering. I guess the bonding is much stronger with the latter.

Which PCB rivets to buy?

I recommend 0.8mm outer diameter (0.6mm ID), because there their heads leave just enough room to route a trace between them. Hence in EAGLE CAD, I make sure to configure my vias to be 0.8mm accordingly, so they fit tightly.

Wednesday, July 5, 2017

Measuring micro amps, the easiest way

You can build yours (see my former review), but you can buy them already made: these $10 sub micro ampmeters on ebay work pretty well from 50mA down to 0.001mA. This range matches nicely the currents of many sensors, including when they are in deep sleep mode. This range is very convenient for IoT autonomous projects and sensors, and the 5 digits makes it unnecessary to switch between milliamperes and microamperes like on a multimeter.

You lose one digit when plugged backwards. The feature is not really interesting except that it makes it safer (you will not burn it by accident).

$10 for these micro current meters is a bargain!
They really are straightforward to use, and they do measure very low currents: the display goes as low as 0.001 mA, ie. 1µA, but I am not sure it is reliable at that level -- anyhow, below a few micro amps, the self-discharge rate of a battery usually becomes not negligible, so there is often no point in fighting further to reduce the sleeping currents. A CR2032 coin cell can run for years at this level, so you would better start optimizing also the wake-up consumption (make sure to read this impressive in-depth review on the matter!).

Sunday, April 2, 2017

Vertical wire spool holder, under my desk

It is quite convenient to store stuff vertically under my desk, because it spares place above it :)

In this regard, I made a very simple but efficient holder with a plastic tube, a screw, and a bolt. It stores some of my spools of wire (show here with the 30AWG single core spools I use for wire wrapping, perfboard, or some repairing jobs). 
        



















When I need some wire, I usually detach the entire bunch without removing individual spools.
The next thing would be a horizontal stand when I need them for a long period over my desk.



Sunday, March 26, 2017

Recycling CD cases

For years I ditched CD cases, but, interestingly, I eventually found some use for them in the last two days. I start regretting the many I should have kept...

CD case as material for an engraved logo. I really did not expect it to produce such a nice result.
Light coming from aside gets scattered by the scratches (I should try adding SMT leds sideways).
The trick was to move quickly, to avoid melting the polycarbonate.

And used as for the bottom protection of a Smoothieboard (which drives the aforementioned CNC mill)
CD cases do break too easily, but they are very convenient as they leave the signal names clearly readable.

Tuesday, March 14, 2017

Arducam too unstable to be useful

The costly Arducam Mini 5Mpixel camera module.
Warning, read before you buy, I do not recommend it!
After weeks of fighting I came to the conclusion that the Arducam ecosystem is useless, and even counter-productive to me -- while its original goal was obviously the opposite.

These camera are sold to provide pictures to Arduinos and other microcontrollers. The Arduino does not have enough memory, so these boards embeds enough processing power (FPGA?) and on-board memory to bufferize it and allow for serialized data to be stored and then transferred on demand. This way, the Arduino can store on an SD, or send it over GSM as I needed.

Now, the hardware may be nice and promising, but the software is really bad in my opinion.

This is strange to me as the Arducam is a wellknown project, and it is costly: I paid 43€ on watterott for example!

But it did not help me work faster, on the contrary. I really had all kinds of problems with the software, trying to interface both on a Uno or on a Mega.

The examples are half-baked, the API code source and the entire library is bloated with tens of variants of boards (28MB zipped just for the Arduinos!). Even the links to source code examples on some product page are broken. All in all, I consider that this somehow expensive camera is barely usable as it produces way too often invalid JPEG streams.

Monday, March 6, 2017

Cheap plastic boxes and enclosures that are just plain good

Below is is a collection of many of the sizes I found on Banggood, mostly to give me a real life feel of the stuff and to have them ready for future projects. I never have the proper box and I often revert to 3D-printing. But they do not look always as neat or they are not as weatherproof as a regular box for some outdoor projects... and it takes a long time to print in any case.

Probably not comprehensive, but a first-hand evaluation of many of the boxes found on Bangood.