Sunday, April 14, 2019

Hack to prevent (solder) wire tangles

I just bought at Farnell some really good and really thin solder wire for small jobs.

The issue is the roll does not hold the wire coils enough si it keeps on creating knots.

I finally came down to this simple idea, which makes use of an elastic band that was offered by a random Chinese reseller, but a regular wide elastic band is probably as efficient. Just pull the last unwound wire under the band and it will hold the coils in place.

Tuesday, March 19, 2019

Pogo-pin harness to stress-test an electronic module before it gets soldered

Here I am using retractable pogo pins again (see a previous use here), within a little 3D printed harness.

This electronic tool holds modules both quickly and efficiently without any soldering. This way I can test or program them individually before they are eventually soldered on the final board.

Obviously then, things get much harder to debug, and sometimes you do not even have room for ICSP pins to test in-situ, or to re-program a microcontroller.

Wednesday, October 24, 2018

Warning/issue with micro-USB ZNTER 1250mAh AA rechargeable batteries


These rechargeable AA batteries sold under the ZNTER brand are cool... until they are damn too hot.

Actually, one of mine started to smoke heavily. Too bad, I like the idea for technophilic trekkers like me, as they require no bulky AA charger. I did not use them a lot though, and I bought 4 more lately so one was perhaps only defective on arrival (DOA).

Anyhow, the charging circuit is probably wrong if it can get to this point without shutting down. It even killed the plug from the 4-way micro USB cable.

In the end: do not buy, or at least do not charge without an eye on them!

ZNTER 1250mAh "AA" rechargeable batteries, which have an embedded circuitry powered by a micro-usb plug!

Friday, May 18, 2018

Script to add a Let’s Encrypt free certificate to an existing Lighttpd web server

Add Let’s Encrypt Certificates to Lighttpd

I wrote a bash script to help add a let's encrypt SSL certificate to a lighttpd web server via the console. Weirdly, they only provide fully automated support for Apache and Nginx as of now (but anyhow, I like to do it my way).

I highly recommend doing so not only because their certificates are free, but also because they help a lot reducing the usual manual burden to install an SSL certificate on an existing web site.

Sunday, October 22, 2017

Lost component 04H-10 5873J01

04H-10 5873J01? No such references on the internet!
The little tabs are still a mystery to me.
I had a bunch of these SMT components which I did not index properly 4-5 years ago (promised, that was the last time I ever was lazy). Sadly, their reference 04H-10 5873J01 brought nothing back on the whole internet... They came in proper SMT strip and they are large enough to sport decent markings though. Alas, I called for help on G+ and/but I ended up sacrificing one open. Initially I thought they were atmospheric pressure sensors, because of the opening to the side.

But no, they are just completely dumb SMD electromagnetic buzzers. The kind with an old-school little coil that pulls a small metallic disk. Nowadays we tend to see more of the piezo electronic kind, but they still have a role because they slightly smaller and they work at a lower voltage (they are just bad in every other respect!). Being passive, they also need variable current to emit sound (they simply click once with a constant current), and I suspect they are able to vibrate at more than one frequency, i.e. they might be able to transmit sound and voice when a piezo buzzer cannot. I would have to check these ones, but I do not expect their frequency response to be good anyhow.

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.