I bought this must’ve been 2016. It was a bad move from the get-go, because the hard disk is only 32Gb. And it had Windows 10, and 32Gb is only just enough to get Windows on. Pretty soon I had to use an outboard hard drive to be able to update windows, and by about 2019 even that didn’t work. It’s a shame, because it’s otherwise serviceable, but totally non-upgradeable – the ‘hard drive’ is an eMMC soldered to the board. It lasted me three years. I did like the light weight and silent operation, but the overall gutless performance and slower and slower startup was bad.
I could use a linux laptop
I had been tinkering with a Raspberry Pi4 for amateur radio field use, but wrangling a Pi in the field for things like SOTA is a mess, because a Pi plus all the odds and sods you need to make it work is a collection of parts flying in loose formation, and unlike a DC3 they don’t always work well together. It’s bad enough connecting the computer to the radio via analogue audio connectors 1, having to connect the Pi plus screen to a Bluetooth keyboard plus some sort of battery to USB-C power contraption gets a bit much in the field although it all works fine on the bench. I had already run the FLdigi and WSJT-X software on the HP Stream in Windows so I knew it was capable of decent performance, better than the Pi4 which struggles a bit to decode WSJT-X in a reasonable time.
However, I had heard bad things about trying Linux on the HP stream, because the Wifi card is very proprietary. The Ubuntu drivers seem to have fixed that now
It was surprisingly easy to load once I quit trying to install on the UEFI BIOS. I uses Xubuntu LTS 20.04, downloading the iso and putting this onto a USB stick using balenaEtcher. I found the install instructions for Xubuntu hard to find and sketchy, but they are good enough to feature this hint
If you don’t already know how to install Xubuntu, then please read this great tutorial, which applies as much to Xubuntu as to Ubuntu.
which is indeed great, and took me from there. But first I had to switch off the UEFI BIOS. It’s not that obvious to me what advantage UEFI gives me with a machine with a whopping 32Gb of disk space which is far from the 2Tb limit UEFI is supposed to fix, so legacy is fine with me.
A disadvantage of linux on a laptop, apart from the general gangly geeky oddballness of linux on the desktop as opposed to on the server is battery life is not optimised so well.
I was fascinated as a teenager by biofeedback, which was big in the 1970s and early 1980s. It’s called neurofeedback now, at least in the EEG guise. Technology and digital processing has made this easier, though some of the fundamentals remain. Wherever you see a puff piece about the latest and greatest dry electrode technology, be that from Muse or from some games gizmo, you are not getting optimal signal quality, because the Holy Grail of the messless EEG pickup has never been found 1. You can get some sort of signal using dry electrodes or capacitive tech, but the EEG signal is weak, in the order of microvolts, so things like Muse and EEG games controllers are frustratingly inconsistent, sort of serviceable but not great IMO. Colour me a cynical bastard but I suspect poor signal quality is why it seems to be the devil’s own job to get the raw EEG data out of Muse, although this and this indicate it might be possible. You’re stuck on a F7-F8 montage with Muse, although that has the advantage of being outside the hairline.
I found Muse a mildly expensive mistake/rathole. I could get somewhere with it, but it was frustratingly inconsistent, I found it stressful using a phone as the interface and the dumbed-down interface grated. I was glad to give it to someone who will use the product as it is designed.
I was intrigued way back then by the Dragon Project, an attempt to measure effects around ancient sites. The physical monitoring part of that project didn’t yield anything of note, but one device they did use was called a mind-mirror, a transportable EEG, there are some pics in their gallery.
This was designed in the late 1970s by the late Geoff Blundell of Audio Ltd, a heroic piece of analogue design to make a multichannel audio spectrum analyser using hardware.
I managed to get one second-hand since publishing my first article on the Mind Mirror. This didn’t work properly – the right-hand side didn’t display right, one of the LED channel boards was down and there was an odd output from the lowest frequency LED display. It’s challenging trying to fix something with no circuit diagram, particularly when it is something that quite this one of a kind, you can’t draw parallels from other designs.
Mind mirror display daughterboards
However, what made this easier is the display is made up of plug-in daughter boards fed in parallel.
one of the Mind Mirror daughterboards
This made it easier to isolate faults and by swapping boards trace whether the issue was on the board or the common backplane drive.
At first this was a sick puppy – the left hand channel didn’t work at all. I compared this with the right hand side, discovering the quiescent signal voltage was 0.82V as opposed to 2.5V on the right hand side. The 5V power line on the RHS was mirrored by 1.7 on the left.
So I pulled display boards till I found the offending board dragging down the power supply. The LHS still didn’t work, so I traced the input signal to a 4016 CMOS analogue switch which had failed on one section. Changing the chip cleared this fault, so I replaced the daughter board till I found the one that pulled the power supply down, which turned out to be a faulty CA324 quad opamp.
The last fault was a weird display on the lowest RHS channel. That turned out to be a duff LED gone short, which due to the odd Charlieplexed display on the UAA170 made me first suspect the UAA170. These are still available NOS on eBay, but swapping the chip didn’t fix the problem. Modern LEDs are much more efficient and a slightly more orangey red than the 1970s ones, so I had to shunt the replacement LED with a resistor to balance brightness.
The unit was originally designed to work with two 6V SLA batteries, but the strip on the PCB joining the mid-point of batteries is not connected to anything else. This is a 12V unit, though the system ground is not connected to the battery 0V.
Tracing out a daughter board was tiresome. an example active filter is
Mind mirror active filter schematic
and simulated in LTSpice this is
Mind Mirror 16 Hz filter LTSpice simulation
This reasonably matches the expected display. Bear in mind the display is linear steps up to 16 levels, so the difference between minimal display and full-scale is about 1:16 or about 24dB, so if all LEDs are lit by the peak the display will extinguish (show the lowest LED) for the same amplitude frequencies < 12.2 Hz and > 20Hz.
The output of the filter goes to a pin on the DB25 socket, and is rectified and low-pass filtered before going to the UAA170 16 LED display IC on the same daughter board.
I have set this on soak test for a few days. In the video the 26Hz channel is off on the LHS, this was due to an unsoldered joint.
unsoldered joint. The messy flux residues aren’t my work, but I figure if it doesn’t cause grief after 50 years I will leave well alone, though I did solder this input to the high side of the level pot.
To feed the signal in I made a special differential driver from a quad opamp and padded the output down. I did test the input impedance which was of the order of >100k, though it got noisy with 100k source impedance. I suspect there’s another one of those CA324s on the input stage. There’s nothing that special about the CA324 nowadays. The datasheet is silent about noise performance, speed is similar to a 741 opamp. It is specified to work down to 5V , and the input common mode goes down to the negative supply, which has the edge on a 741. Looking at the internal design, there’s much in common with the nasty2LM358 and indeed Texas Instruments lump the LM324 and the LM358 together in this application note.
You can do a lot better now, I’d be tempted to run it on the 100uV range and use a preamp to get a higher Zin, though I should test first. Perhaps the high noise is the 100k source being amplified so much – the specification is for a 10k typical contact resistance. You can only achieve this with wet electrodes, which is something I have yet to wrangle.
The spaces top left and right was originally to take two 6V sealed lead-acid batteries, nowadays the same capacity can be had in much less space in NiMh or a 3S LiFePo drone battery.
In the meantime I also got the Olimex EEG-SMT to tinker with. Although I feel the openEEG antialiasing filter leaves something to be desired I didn’t observe shocking levels of interference so perhaps I was overthinking that. Reading the archives of the openeeg mailing list I was impressed with the care taken over the analogue design, to the extent an easy win would be to use the EEGSMT in the LHS battery slot and break out the analogue signal from C51 and C52 to go into the MM. The driven right leg grounding scheme of openEEG works very well, and I verified that messing about with the EEGSMT and a pair of Olimex active electrodes used dry.
Sadly I screwed up buying only two active electrodes, since the channels are differential you need two active electrodes per channel, four in all. Since the UK has left the EU there is a whole world of hurt associated with buying from the Bulgarian company Olimex that I didn’t have when I bought the original devices a couple of years back.
However, I have a working Mind Mirror EEG and a serviceable Olimex OpenEEG system. After a frustrating foray into the dry electrode world of Muse, I can return to tackle the problem I never faced up to, which is eschewing the mirage of decent dry contact solutions. There aren’t any, because you cannae change the laws of physics. Dry contact solutions means higher contact resistance, which associated with a weak signal coming through a high resistance means more noise and less signal. I need to suck that up, because I have wasted too much time on that sort of thing.
Nasty because these damn things are responsible for a lot of audio crossover distortion when used by tyros drawn to the low cost and low voltage performance. See TI application note page 17. If you really must use these at audio frequencies, pull the output down to the negative rail with about 10k to bias the output push-pull NPN Darlington into Class A. The TI app note preamble The LM324 and LM358 family of op amps are popular and long-lived general purpose amplifiers due to their flexibility, availability, and cost-effectiveness. It is important to understand how these op amps are different than most other op amps before using them in your design. The information in this application guide will help promote first time design successes. should warm you up to ‘here be dragons’↩
The Logitech C920 is a lovely little webcam, and having the MP4 conversion on the onboard processor means you can use it with gutless hardware. I got mine as a cast-off from Jason at Wildlife Gadgetman and wanted to use it for video-conferencing, what with the coronavirus lockdown and all that.
Trouble is the damn thing is short-sighted. It seems to be a common problem with the C920, and the autofocus is ratty. Sometimes it would work, sometimes not.
I am short-sighted too, so a temporary fix to get it to focus on distant objects is to Sellotape one lens my glasses over the front, but it’s not a good look. AF was still ratty. Poor distant focus is a common complaint with the C920. This fellow shows you how to take it to bits
but unlike him, my fault was the little piece of metal had become loose and was fouling the movement of the lens.
the squarish metal washer with three notches had come adrift.
Extracting the washer from the lens, using the notches to pass the castellations on the lens mount let me isolate it
I did consider leaving it off
but figured I’d get flare from reflections from the plastic cover in front so I used thick superglue, carefully to avoid getting it on the lens. Four dabs at the corners sorted it.
Job done, sorted. This doesn’t seem the only way for these cameras to misbehave on focus, and unfortunately you can’t see the errant washer because of the baffle on the plastic cover. But you have to take it to bits if your problem is the focus is off as the one in the video. There’s a neater way to do the glasses thing with an eyepiece adapter lens as in this video, which doesn’t entail taking it to pieces, but that wasn’t the problem for me.
This post is as a public service. WARNING – an Olympus E-PM1 camera has some LEFT-HAND thread screws. I’ll show you where these blighters are later.
Manufacturers really seem to hate people taking their gear apart, but I’ve never come across Olympus’s sort of craftiness before. There’s no good reason for them to make these screws left-hand thread, other than to make you strip the soft plastic they’re set into if you have the temerity to try to take your own property apart. Evil bastards. It’s not like a bicycle crank on the left-hand side, where there’s a damn good reason for the left-hand thread.
I quite liked this camera, despite the plastic battery door hinges breaking off after a year. It’s pocketable, but can take a decent EVF if necessary, I have a VF-4. I recently dropped the camera, and on power-up I hear this noise (recorded form about 2cm away). The clunk is fine and has always been like that, the death rattle is new.
Which does not fill me with confidence that this camera is long for this world, although the pictures are fine. I can almost count the plastic gear teeth wearing, and it’s loud enough to draw attention, which is a drag for photographing people. I suspect it’s slower off the mark than it used to be, too. So I thought I’d pop the back and take a look to see if something is obviously wrong. Continue reading “Olympus E-PM1 camera left-hand thread screws to catch fixers out”
note – this is a Mk 1 version of the Canon EF 100-400 L
A working photographer uses their lenses all the time and probably never runs into this. I was into bird photography for a while, about eight years ago, and had the Canon EF100-400 IS L like every other wannabe bird photographer. In between now and then the field has separated the sheep from the goats – real bird photographers use longer primes, because the birds are always at the long end of any zoom. Or they use astro scopes on manual focus 😉
Lapwings landing
Anyway, I take time out from birds and photography, because life gets in the way, and I stow the lenses in a relatively cold room. A couple of years back I figured I’d take some long lens pics, and get greeted by this
Lens fungus. Nasty
which makes me curse. Mainly on the front element, though a starting spot on the inner element, which is part of the IS mech. The inner part is magnified by the biconvex front element. The spotty crap is on the inside of the front element, the fine filigree round the edge on the front of the front element. Continue reading “Canon EF 100-400 L lens fungus attack”
