Uvicord II

 

The Uvicord II has a pretty fascinating way of running the UV lamp: The light source is a sealed quartz glass tube with a little zinc or mercury in it (depending on the desired spectrum), but it has no leads! Instead, it is externally heated at one end (see below) and the energy is transferred by high frequency capacitive coupling into the tube. Like when you bring a fluorescent lamp into a microwave oven or similar if you move it close to a charged old fashioned CRT :

Gas at low pressure + alternating high strength electric field -> ionized gas -> light!

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Fig. 1: The PCB

Fig. 3 shows the reconstructed schematic of the lamp driver: It generates a high frequency signal which is capacitively coupled into the light source tube. The power is supplied through P1 and the HF current is coupled into the gas tube with metal rings connected to the ends of the coil (depicted as P2), they are located at the reverse side of the PCB (Fig. 2).

uv-driver-svg

Fig. 3: The reconstructed driver schematic

The easyeda file: uv-driver_easyeda

The NPN transistor, originally a BSX53 (30V, 100mA, 130V, 300MHz, Ic/Ib=75..750, of which it was quite difficult to find a datasheet, the PCB is from 1987, almost 30 years ago and the board still reads “LKB”) was supposedly and apparently dead (I tried to measure its hfe with my DVM, it turned out to be 0, i.e. no response). So I replaced it with a 2N2219A which has similar electrical characteristics (UCE 50V, 800mA, 0.8W, 300MHz) and the same case (TO-39, to re-use the heat sink).

The gas tube is heated at one end by a BD179 transistor (30W, UCE 80V, IC 3A, IB 1A) mounted to the lamp holder as heat sink.

Notes & Acknowledgements:

The schematic was created with the free SAS online editor at easyeda.com.

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Taiwan TaKeDa and Mobile Data Access

This is how I spent a week-end without having much fun: Making Taiwan TaKeDa mobile Network APN work on an unbranded Dumbphone!

Opted for a data plan. Got even a call that it had been activated on August 1st after lunchtime. Of course, didn’t work: Got a “wrong APN settings” error message. Went to one of their shops. They concluded my mobile (a HTC one plus, obtained from SingTel as a “free” gift to our communication package there in 2012) had a problem. So went home again and finally found an excuse to transplant the working mainboard from a HTC Sensation XE (but a broken screen) to a HTC sensation XE with a working screen (but a broken mainboard). Sometimes it makes sense when you and your TaiTai have the same models of hand phone, this really may save you money if you are able to perform micro surgery on micro electronics! The two phones had been bought without contract in Taiwan some years ago. Finally, I got another perfectly working Dumbphone, but still the mobile network still would not work.

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Resurrecting a VWR Galaxy 14D Benchtop Centrifuge

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VWR Galaxy 14D, back alive!

It had been advertised as “does not power on” and I got it pretty cheap on eBay, below 100USD including shipping from the U.S. to this beautiful country.  Assuming the usual culprits for a “complete failure”, when the cosmetics are fine: a broken switch or a blown fuse, it should have been an easy fix and a good bargain for a used item sold new for 1400USD.

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C++: Outputting a string as hexadecimal characters…

… is easy with the boost format library:

Digging the net for examples was not very productive, so I started my own approach:

The trick is the “%x” which will output the numerical value (uint)s[i] as hexadecimal value.

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Unterwegs auf dem NenKao Trail – 6 Tage zu Fuß durch die Berge!

Unterwegs auf dem NenKao Trail – 6 Tage zu Fuß durch die Berge!.

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OsziFox / ProbeScope in Xubuntu 14.04 LTS

2014-07-01_21-02-19_CH1On my system, it runs with wine and a USB to serial adapter and the FoxiOsz program (originally for WinXP), by Michael Butschkau, to be found here: http://www.mikrocontroller.net/topic/167705. Thanks and Kudos to Michael for this! The site offers 3 versions, just get the latest one (v1.1 at the time of writing).

You probably have to tell wine to use /dev/ttyUSB0 (or whichever number) as COM1 (or whichever number) and make sure that your humble userness has the right to access it: Make yourself member of the group “dialout” and add a symbolic link in ~/.wine/dosdevices:

ln -s /dev/ttyUSB0 com1 (or whatever)

If in doubt where your USB2Serial device might show up, you may check it with “ls /dev/ttyUSB*”.

 

 

 

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Repairing an LED light bulb

One of my beloved power saving LED light “bulbs” suddenly stopped working, far before it had reached the end of it’s promised and assumed 50.000 hrs lifetime.

A good occasion to dissect the poor device and to try to repair it, or at least: trying to understand how it works!

The dissassebled "Lightbulb"

While the LEDs were accessible by removing some screws and could be verified to be ok with the diode testing function of a cheap DVM (they lit up slightly), it was a bit tricky to access the actual electronics (in the socket, the device that is converting mains AC to about 9.5 Volts of DC (measured) – the LEDs are in series). I finally was successful with a drill (see picture), making holes into the socket pins at 2 positions each: First, in order to sever the wires to the PCB to get it out and also to create new holes to enable the rewiring with new leads later.

The extracted power supply

The extracted power supply

Some basic tests (signs of burn, fuses, rectifier, diodes) did not reveal any faults. Interestingly, when connecting the opened device to AC (actually, to perform some in situ checks), and after I started worrying about obtaining an MJE13003 in a TO-251 case (TO-220 is too big, TO-126 might not fit, too) or an AP3706 for a reasonable price), the light simply worked as nothing had happeed. Seems, the problem was a bad “mechanical” connection of one of the wires at the socket. Added some new wires to connect to the socket and reassembled the whole thing.

Now I am enjoying my resurrected light bulb and am happy about having saved some money and prevented  premature electronic waste.  Although in terms of economics, it was not “reasonable”, the whole project took me several hours. But it’s one of the things you can do to lift up your spirits while you’re waiting for your work permit being processed :).

View on the AP3706

View on the AP3706

Some background: The whole circuit is constructed around an AP3706 controller (3rd picture), a driver for switching power supplies. For a prinicipal schematic, see the application note e.g. here: http://www.diodes.com/_files/products_appnote_pdfs/power/sw_reg/AN1028.pdf. Not many things that actually can break down: A 1A fuse, the AP3706, a MJE 13003 NPN power  transistor and 2 diodes. In any case, it might be worth not to discard such a device, just because it has stopped emitting light.

For soldering on the LED plate and on the sockets, you’ll need a high power soldering gun (mine has 1kW) or something similar. A standard 50W soldering iron won’t work, due to the high heat capacity of the aluminium (cooling) plate that holds the LEDs and of the socket contacts. However, to fix the new leads at the green PCB, a standard iron is the better choice.

Although it won’t make much sense to buy replacement electronic parts as you’ll spend almost as much as a new light bulb will cost you, it should make sense to keep “burnt” ones and use theirs parts as spares.

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