At last summer’s Ham Radio in Friedrichshafen, I was offered a YIG-tuned oscillator at the suspiciously generous price of 5 Euros. Since I’m always on the lookout for cheap instrumentation-grade YTOs, I took it without a second thought. After a brief chat with the friendly operator who sold it, I learned that it came from a recently discarded HP spectrum analyzer, which appears to have been beyond hope. However, he claimed that the oscillator worked ’til the end. Should he read this: thanks for the chat, and for the part :-)
A few months later: Grabbing a spectrum analyzer and a bunch of power supplies shows an indeed very healthy part.
Yes, this is about fancy displays – again. I have been wondering for a while whether it could be simple to repurpose the LED matrix displays often found in Jura coffee machines. Mounted behind tinted plastic they give the front panel a distinctly premium look. Coincidentally, they look highly similar to the Osram- and Avago-made PDSP/HDSP intelligent dot-matrix module series, which is what I was initially expecting to find when pulling apart the control panel of a scrapped Jura Impressa C9. Let’s just say the expectation was pretty far from the mark.
By using this GPIO drive mode it is possible to offload framebuffer output to the hardware, which brings speed and saves a huge amount of CPU resources compared to bit-banging. This interface is frequently used for outputting VGA signals, since it is one of the original display signal output methods of the Broadcom CPU for driving parallel TFTs or LCDs. Obtaining analog VGA from it requires a resistor ladder DAC board [3], which combines the individual digital bit signals to analog multi-level RGB signals. In the case of a TFEL display this is not necessary, since the control circuit accepts digital level VGA. However, the clock mode is a bit unusual compared to the common configurations (as explained in previous posts: required is a 640×400 pixels, >70 Hz, monochrome signal).
Yesterday, a discarded Samsung SD863 datacenter SSD found its way to my hands. Although a bit older – this one’s from 2016 – these are supposed to be quite reliable (except for a few rumoured firmware bugs), and 480GB of capacity are not to be disregarded even at today’s remarkable flash prices. Since it did not suffer from the usual drillholes of unreadability, I hooked it up to a linux machine – hopefully immune to virus-infected, supposedly “lost” thumbdrives – to give it a try. Unsurprisingly though, the drive announced 1GB of capacity, which does not fit its type MZ7KM480HAHP and explains its disposal. I had a hunch that the reason might lie with the microcode:
ERRORMOD as a version index looks rather like something went horribly wrong, causing some kind of corruption to the firmware. At least it still communicates through SATA, which indicates some backup capabilities.
As of 16th of July, this site is delivered in a new layout, which *should* be mobile-compatible. The old theme’s backend has become too messy over time due to a lot of hacks I added. I still need to restore some parts of the old design though, so there will be some more change over the next few weeks.
Recently I found some time to move my TFEL driver onto a spare Pi3B to test its performance. First, it still compiles fine on Archlinux ARM 4.14.87 and the GPIO layout is compatible.
Recently, the speedometer of my trusty old Volvo 850 station-wagon started acting up. Initially, it would just drop to zero intermittently at speed, then come back. Hard to notice if you only so much as glance at it every now and then. Over the last two weeks this got worse such that it would only very rarely do anything at all. My best guess for the cause would have been the speed sensor at the vehicle underside, but for mysterious reasons the odometer was still going at the normal pace. According to the instrument schematics, this should not be possible if the sensor were broken – same signal for both. Continue reading →
Getting a fitting transformer bobbin for ferrites is not easy under normal circumstances, but even more so for cores of unknown type. Usually, the dimensions follow a somewhat standardized pattern, but then your application might demand for separate winding chambers or mounting aids which are simply not available to the standard customer. So why not 3D print it?
The motivation is to use an old ferrite core for a high voltage lab supply. It will be driven far below its theoretical maximum spec as I only know it came from a ~50W power supply. My design (a flyback converter) requires a single winding in single-ended mode for the primary consisting of 23 turns, and a secondary of 235 turns capable of withstanding roughly 1kV. For winding I use standard enameled solid copper wire of unknown brand, which will probably not survive the full voltage. As a solution, I want to separate the secondary into 6 compartments of 40 turns each to reduce the maximum possible voltage between two neighboring wires to a maximum of 166V, which is well below the breakdown range. Without compartments, the left-to-right-to-left layer winding – which will occur somewhat naturally – may cause turns with extreme voltage difference to end up touching, leading to arcing sooner or later. To additionally strengthen the winding, a soaking resin could be applied.
Using the dimensions of the core as a base, some modeling in Tinkercad yielded this:
Tinkercad design ready for STL export.
Finished print in PLA, filed and mounted on ferrite.
Windings inserted, ferrite closed and fixed with PET tape.
A few weeks ago a friend brought me an old subwoofer that was discarded as broken – a JAMO SUB-660, which is an 600W sub for home cinema with integrated amping. The sub receives pretty good reviews, so I set out to try and fix it. I have worked on quite a few power amps until now, but as fully switched designs like this rarely fail, it is always a challenge when they do.
Fig. 1: Jamo SUB-660 power amp module. High-power PSU (right top), standby PSU (right of centre), Class-D amp (above centre) with large output filter choke (centre). Preamp, sound filters and standby detector PCB on the left, line input on the bottom right.
Fig. 1: Archlinux logo running on a raspberry-driven Planar/Finlux EL640.400 display.
Thin film electro-luminescent (TFEL) displays represent an interesting, if somewhat anachronistic display technology, now that we have high-contrast LCDs, plasma displays and of course OLEDs. The latter are actually closest to the principle of TFELs, and their primary optical advantage is identical: light-emitting pixels instead of backlighting, for maximum contrast. Where OLEDs use an organic polymer, which can be excited to emit visible light by applying an electric field, a TFEL does the same with an anorganic dielectric material like e.g., gallium arsenide (GaAs). The emitter pixels are sandwiched between two layers of transparent dielectric to insulate them from the transparent electrode grids on the front and back glass cover of the display panel. When a high-frequency current is applied, a current flows through the selected pixel and the emitter material lights up in a beautiful, saturated orange – in my opinion the most interesting aspect about this technology. Remember the old terminals with the amber CRT screen? Close! In contrast to OLEDs, EL displays are also able to tolerate much harsher environmental and mechanical conditions, which makes them ideal for applications in heavy machinery – or living room gadgets, when they are retired. Continue reading →
