15 September 2014

DIY component tester (kit)

Following a review of VK3YE on vklzqrp reflector, I ordered one of "DIY Meter Tester Kit For Capacitance ESR Inductance Resistor NPN PNP". At 10€ shipping included from Far East seems a good bargain.

The kit is a clone/reproduction of a German project, that has been updated in recent months. Hopefully with some careful comparison of the kit with official docs it will be possible to "port" new features to the PCB I will receive in ... 2-3-4 weeks.

12 September 2014

Mind cheap technology around Li-ion batteries

I was given a LED torch that included both 12V DC and AC chargers, and a 14440 Li-ion battery.

The AC charger circuit exposed.
The AC charger was faulty at the DC plug towards the torch. Discarded right away. A further inspection at a later time revealed a properly designed DC supply.

The 12 Vdc charger exposed.
The cigarette lighter 12V DC charger worked, so I used it to top-up the battery right inside the torch. Since the charge was not coming to an end, I interrupted it and measured the battery voltage: 4.7 V !! What?!?? A Li-ion charger is supposed to be produce no more than 4.2 V(*). Else ... it can catch fire.
I opened up the cigarette socket charger and found a 78L05 voltage regulator and an open-circuit voltage of 5 V. That thing is simply d a n g e r o u s !

12-to-5 V circuitry. The large resistor limits dissipation on the linear regulator, while the LED is connected across the 12V input with a 10k series resistor.

Now, either the cable from the dangerous 12 V charger will be transplanted to the AC charger, or I will add a series diode to drop the voltage to a safe(r) amount.

But, how about the remaining 99.999(9)% of world population that will buy similar products and never question their technical properties, thus trusting the producer? Either the product will fail early (most likely), so they'll blame Chinese manufacturing, or get hurt (heat, fire) without anyone to complain to. I am aware there is no solution, at least in the Country where I live.

(*) If you are in a hurry, a Li-ion battery can be charged at a constant voltage of maximum 4.2 Volts per cell. Do keep an eye on it and measure stand-alone cell voltage every 30 minutes. Disclaimer: do it at your own full risk.

10 September 2014

RFID 2nd generation (in operation)

While preparing for Winter storage my sea/beach/snorkeling equipment, incidentally I came across a new form of product tracking. I had to remove the insole (sock liner?) from an aqua shoe because some sand had gone underneath and found ... an RFID tag!

Since the design was different from those I had already seen operating on MF or HF, a web search was due. Then I found out about RFID Gen 2 related to a form of Electronic Product Code, an electronic version of the good old barcode.

These things shown in the picture work at around 900 MHz (in Europe), have a larger range than previous RFID technologies and allow multiple items to be read at once. It is supposed to facilitate the management of shop stocks and inherently includes anti-theft since it is probably just a flag in a complex tag.

A visit to the sports supermarket has shown this new technology in action, with many false alarms at the exit anti-theft gate, including my purchase. Just wondering how much RF power the reader/writer throws out.

Reader/writer hardware for these objects still costs 150-200 USD, so it is not yet time for hardware hackers on a budget to kick in. In any case I am keeping these tags for you-never-know...

02 September 2014

Restore data from broken NAS

(Versione italiana in fondo)

One morning the colleague on my LHS arrived quite sleepy and worried: his home Network Attached Storage stopped working. He was up late trying to have it acquire an IP address from the router, without success. That WD My Book World Edition had no USB port, only network, so there is no way to access the disk.

After a couple of days I convinced him to bring over his disk so that we would have a look together. He was convinced to be using a unit with twin disks in RAID (Redundant Array of Inexpensive Disks), but we found only one inside when we opened it up (no pictures)!! We plugged the one and only bare disk into a SATA-to-USB adapter. The disk spin up just right, but MS Windows couldn't see the data in it. A quick tour with default Windows system tools revealed four partitions: a Linux-like system was in the disk in front of us.

Since we had no Linux desktop, I fired up an Ubuntu Linux virtual machine and let it see the disk. Disk partitions were all in raid format (but remember, no other disk could possibly fit into the case!), and the array was "busy". Few web searches ahead and in three shell commands I was into the right disk partition and could see all his precious data.

Then it was just a matter of plugging another USB disk and copy data out of the NAS disk.

**** ITALIANO ****

Una mattina il collega alla mia sinistra è arrivato molto più assonnato e preoccupato del solito: il suo disco di rete NAS di casa aveva smesso di funzionare. Aveva fatto le ore piccole cercando in tutti i modi di convincere il NAS ad essere di nuovo in rete, ma senza successo. Siccome il WD My Book World Edition non ha altri accessi se non la rete, non c'era modo di accedere ai dati.

Dopo un paio di giorni l'ho convinto a guardare assieme l'oggetto e lo abbiamo aperto. E' stata una sorpresa trovare un solo disco dentro il box, mentre avrebbe dovuto essere un array ridondato (tecnicamente "dischi in RAID"). Quando abbiamo inserito il disco in un adattatore SATA-USB ovviamente non ci sono stati rumori strani o fumate nere: funzionava tutto a dovere, ma Windows non vedeva nessun disco utilizzabile. Con gli strumenti di gestione del sistema abbiamo visto che il disco conteneva le quattro partizioni tipiche di un sistema Linux.

Siccome non avevamo a disposizione un computer desktop con Linux in cui impiantare il disco, ho acceso una virtual machine Ubuntu Linux sul portatile e le ho "mappato" il disco USB. Tutte le partizioni erano in formato raid e l'array era in stato "busy". Dopo alcune ricerche in rete (con annesse letture approfondite) e tre comandi shell ho avuto accesso alle partizioni e individuato i dati.

Dipodichè è stata semplicemente una questione di collegare un secondo disco USB alla virtual machine e trasferire i dati.

A quanto pare questi NAS casalinghi sono soggetti a fallimenti nell'elettronica, mentre i dischi rimangono sani. Se doveste ritrovarvi con un Western Digital My Book World Edition irraggiungibile, provate a contattarmi.

28 August 2014

Virtual Audio Cable for Android (not!)

I want to be able to listen to the receiver in my shack while doing other things around the flat. I wanted to do it with a Bluetooth headset paired with an Android smartphone, so I need a simple "virtual audio cable" app that pipes the audio from the physical micrphone over to the BT headset. The app could also provide additional functionality, like squelch or CAT control or even the ability to reply and transmit.

As of today I have not been able to locate a suitable Android app. I tried to build one myself using MIT's App Inventor, but their Bluetooth library supports data transfer only, not audio (August 2014).

I will have to use a stand-alone headphone+base. They cost about 10€ in Far East but they transmit in the FM broadcast band, which is not license-free in Italy and it is too crowded for any low-power signal.

Case closed.

20 August 2014

Solar lamp experiments

My family owns a solar lamp bought at the popular Swedish furniture shop. Given the amount of light it can produce, all night long, I had to take some measurements to understand how much power the same hardware could deliver to a stand-alone circuit.

What am I thinking of? Something like an off-grid sensor that stores data for large amounts of time before any human intervention.

One doubt was: does the cover influence the amount of light reaching solar panels? If so, how much?

The twin solar panel is used to charge a 1.2 V NiMH battery. I decided to measure the current flow through the battery. The experiment was carried on with the help of my daughter: connect crocodile clips, read the ammeter, put the cover on, ...

The discharge current is just above 16 mA, and the lamp with 4x 3 mm white LEDs is very bright. There is a nice step-up circuit in there. That's 19mW out. A fully charged 2000 mAh battery could keep the light on almost 100 hours.

Having never measured a live solar system, I did interesting discoveries.
Without the cover, in full sunshine and oriented right at the Sun, the circuit pushes 100 mA into the battery (120 mW). Put the cover and current goes down to 80 mA. I didn't expect those small solar panels could produce so much current! But that's the optimum condition and requires something to track the Sun: could it be energetically worth?

What happens on a cloudy day? Recharges at 5 mA without cover, down to 3.7 mA with the lamp cover. That's 6 mW instant power, a huge difference from a bright day!

Another interesting discovery about the lamp was that it keeps charging even if the switch is OFF, meaning that you can let the battery top-up when you don't need the light at night.

In the next episode. Considering a 70% charging efficiency for NiMH technology, how much power can the stand-alone device drain for prolonged use? Would it be worth to track the Sun?

14 August 2014

70 MHz progress - August 2014

Thanks to some amazing Es openings last July 2014, my 5W and Moxon beam allowed me to reach 7 DXCC (I, G, GM, ES, 9A, OH, YO) and 8 different squares.

Few more countries should be possible, even though I probably need to move the antenna to the balcony facing South to work EA and CT. Or build/use a second antenna and run a coax through the whole apartment.

Now that the Es peak is gone I can concentrate in working neighbouring squares, like JN34 and JN45. The only station I heard from JN45 is a big gun and we will arrange a JT65 QSO, possibly with the help of aircraft scatter, because 2x SSB was not successful.