Among my recent electronics purchase spree was the amazing Teensy LC from PJRC. It has a nice ARM Cortex-M0+ processor, real hardware USB, and what’s the nicest part, an Arduino add-on called Teensyduino which enables easy programming with Arduino, but with support for many of the hardware features.
Now I started playing piano a while ago, and just a few weeks ago bought a Pianoteq license to send notes via MIDI to my computer, and render high quality piano sound to speakers. However, it turns out my $8 USB-MIDI adapter from DealExtreme had a less than perfect implementation, essentially changing pedal events into “note on” events!
Thankfully, I had a MIDI connector and a high-speed optocoupler at hand, and with these I could implement a MIDI in rather easily. After some investigation with Arduino Uno, it seemed quite simple to receive the serial MIDI bytes and dump them over Arduino serial (I’ll write another post about this later).
However, Arduino cannot become a USB MIDI device very easily, so here comes the really nice part: Teensy LC can, and the Teensyduino add-on included a working USB MIDI and also serial MIDI libraries!
The Wikipedia page for MIDI essentially shows the required circuitry for receiving MIDI data – wire the DIN cable pins 4 and 5 through the receiving side of optocoupler and put a 200 ohm resistor in series with it. A diode is also suggested for reverse current (ESD) protection, but I skipped that. You can start with a LED instead of optocoupler to see it lights up if you’re unsure you have pins 4 and 5 the right way. Or just put the LED (with a resistor) on the other side of the optocoupler first.
The HCPL-2531 I had at hand requires an additional VCC connection on the sending side. After some experimentation, a 4k7 ohm pullup resistor between VCC and VO1 (NPN-transistor base?) gave the cleanest signal out. The wiring diagram (thanks Diptrace!) is shown below:
Continue reading MIDI to USB Adapter with Teensy LC
Happy New Year 2016! After a long hiatus in electronics, I have been quite busy in the last month or so. I have a bigger (USB MIDI related) project posting coming up, but just wanted share a small nugget already.
I ordered a big chunk of things recently from Adafruit shop and Sparkfun. Among them was the lovely Adafruit Trinket (which actually came as a free bonus because I spent way too much on black friday :).
Now I am planning a project which involves transforming the very compact, but already USB-enabled Trinket into a USB MIDI device. However, there are two problems:
- Adafruit examples for USB come in Arduino form
- There are no USB MIDI examples
I somewhat dislike the high-level Arduino environment in cases where low-level performance is needed (and the V-USB implementation is one of those places), and for my later MIDI part, I will need fine-grained control to juggle serial communication and USB. Also, all USB MIDI examples are on “bare metal”, so the Adafruit example Arduino code would require deeper knowledge of Arduino inner workings than I have.
Time to do some chopping!
Slimming Down the TrinketKeyboard Example
I decided to adapt the excellent base code in Adafruit Trinket USB GitHub repository, but trim the keyboard example to bare essentials (my next step will be to transform it into a USB MIDI device, so the less code I have to adapt, the better). Turns out this was quite simple to do:
Continue reading Adafruit Trinket USB keyboard without Arduino
It’s been ten months since I got and reviewed the Topre Realforce 88UB. I’ve been very satisfied with the keyboard, the only real issue being that for some reason my brain is having strange difficulties with adjusting to the new microlayout since my time with HHKB — for some reason I still hit adjacent keys quite a lot when coding, getting # instead of % or ‘k’ instead of ‘j’ (doubly frustrating with Vim!).
However, the thirst for new experiences never really leaves you, so I decided to try out the Matias switches that have caused quite a lot of discussion at Geekhack. Since I’ve liked the low thud of Topre keys and loved the compact layout of RF 88UB, I decided I’d see how the Matias Mini Quiet Pro compares to my Realforce.
After using the Matias keyboard extensively for several weeks, I think I have enough experience to write a bit about this new entrant to the rather established Cherry/Topre/Unicomp triopoly of mechanical niche keyboards. To make it more interesting, it’ll be a shootout against the reigning king, Topre Realforce 88UB. Fight is on!
Warm-up Round: Specifications and Price
I got my Realforce through The Keyboard Company in UK, and they were kind enough to provide the Matias Mini review unit for this shootout. As a thanks I’m including their banner here, and based on several years of personal experience I can really recommend them, especially if you’re within EU as there will be no customs fees.
Specification-wise the Realforce and Matias are quite similar with reduced tenkeyless layout sporting function and cursor keys. The Topre has standard pageup/pagedown etc. column whereas Matias a bit more compact but requires a function key to access insert, home and end and the more esoteric print screen, scroll lock and pause/break keys. Price-wise, the Matias sits in the not-quite-inexpensive $160 price range, but the Topre almost doubles this with its hefty $295 price tag.
||Topre Realforce 88UB
||Matias Mini Quiet Pro
||Compact with cursors
||Dye sublimation (black on black)
||Laser etched (white on black)
||Yellow WASD keys and keycap tool
||3 USB 2.0 ports and two cables (long & short)
Continue reading Topre Realforce vs. Matias Mini Shootout
It’s battle time! Some of you may have heard that Raspberry Pi 2 is out with more punch than ever. Just how much more? Well,
apt-get dist-upgrade went about 5 times faster with the new Pi. With 1 GB of RAM and four cores, this will definitely be a boost for my home SSH box ergonomics over the previous version.
But what about hacking? There has been a lot of interest in getting GPIO benchmarks for the Pi 2 similar to my earlier Raspberry Pi GPIO benchmark. Well here it is! Please refer to the earlier article for source code and nice screenshots of square waves, as I’ll concentrate on the performance difference only here. You can also get the code from Github:
Summary of results
All the Pi 1 benchmarks were ran 14th and 15th February 2015 using latest versions of the libraries as stated in my updated benchmark post. Pi 2 benchmarks were all run 25th and 26th March 2015 with the latest versions. If you get significantly different results at a later date, please let me know and I’ll update the table!
|Shell / wiringPi
||WiringPi gpio utility
||WiringPi normal GPIO wiringPiSetup()
||WiringPi GPIO wiringPiSetupGpio()
||WiringPi sys wiringPiSetupSys()
Continue reading Raspberry Pi 2 vs. 1 GPIO Benchmark
This is my review of the Topre Realforce 88UB mechanical keyboard with evenly weighted 45g switches and UK layout. This is the ISO layout sister model of the Topre Realforce 87U (87UB / 87UW) so everything in this review will apply for that model, except a few layout details regarding the extra keys. Before diving into details, a short background of my previous journey:
Two years ago I got really interested in high quality mechanical keyboards. After all, the keyboard is the instrument I use several hours every day, so if I am spending close to 2000€ on a workstation and display, why should I compromise with a cheap 30€ keyboard, especially since the keyboard will likely last several workstation lifespans?
After heavy research I settled on Happy Hacking Keyboard 2 Professional due to its compact “hacker” layout which seemed great for vim, and Topre key switches, which many consider to have the very best tactile feel. See my review of the HHKB2 keyboard for details.
However, in two years of typing with the HHKB, I never fully learned to use function key bindings for cursor keys and Home/End fluently. Coding with Vim somewhat alleviated the problem, but every time with a command prompt or a shell this nagged me. Also, playing games required a separate keyboard, as most games make use of function keys, and many make use of both WASD and cursor keys. It was time for something else. Something better.
Topre Realforce 88UB – Best of both worlds?
After my experience with HHKB, I had the critical components for my dream keyboard well thought out:
- Tenkeyless model with dedicated cursor and function keys. I’ve also used CM Quickfire TK and I can say from experience it is a terrible idea.
- ISO layout, so I get the \ and | right next to my right pinky, and an additional key next to z to get < and > in Finnish keyboard layout (it doubles as another \| in US layout)
- Topre switches for the ultimate typing comfort. Having used rubber dome, scissor mechanisms and Cherry MX blues, and trying out reds, blacks and browns, there really is no competitor. Buckling spring is just too heavy and noisy for my taste.
The items 1 and 2 are quite easy, but the third one essentially meant that the Topre Realforce line would be the primary candidate to fill all these needs. I’ve used The Keyboard Company before and they have a superb selection of Topre models, so I quickly zoomed in on the black 88-key model with UK layout:
Continue reading Topre Realforce 88UB – A Happier Hacking Keyboard
Shut down my Pi today and thought to make a copy of files in its SD card. This is what
mount /dev/sdf2 /mnt had to say:
mount: wrong fs type, bad option, bad superblock on /dev/sdf2,
missing codepage or helper program, or other error
In some cases useful info is found in syslog - try
dmesg | tail or so
Great. After trying
fsck, it became apparent that for some reason, the root partition is marked as being 1 block longer than the physical card. Must be a bug with Raspbian partition expansion or something.
Thankfully, I found this gold nugget which suggested using
resize2fs to fix it. Turns out I had to run e2fsck first (and say “y” a couple of times):
sudo e2fsck /dev/sdf2
sudo resize2fs /dev/sdf2
mount /dev/sdf2 /mnt
Voilá! Fully functioning filesystem again.
The new Raspberry Pi model 2 is out and the Pi world seems more popular than ever. My 2012 benchmark of different RaspPi GPIO access methods has been getting a lot of hits, so I thought to revisit it, and have now updated all the benchmarks with latest versions of firmware and GPIO libraries. I’ve also upgraded my oscilloscope to PicoScope 5444B, so the scope bandwith limitations I had earlier are now gone. :)
Because the benchmark has been linked from many other sites, I’ve just updated the old post to keep links pointing to right places.
Read the updated Raspberry Pi GPIO Speed Benchmark!
Ever had that moment where you started coding X and instead spent four hours doing Y instead? I just had it, and it stemmed from a quite simple idea: let’s do an embedded SVG bar chart with React (nice library by the way)! Because I just started with Bootstrap which makes it really simple to scale your content to the device at hand, I also wanted the diagram to scale. Easy, right? WRONG!!!
<svg version="1.1" width="100%" viewBox="0 0 200 100">
here are some primitives
The viewBox attribute defines the internal coordinates for the SVG, and the
width attribute should ensure the SVG fills the container. And it does, at least on desktop. And mobile Chrome. But not Android default browser. I tried different settings of
preserveAspectratio. I tried CSS tricks that should work but they wouldn’t. After some hours, I gave up and went to sleep. And this morning I found this nugget: WebKit long had a bug, where SVG element is resized to 100% height, which on mobile device was interpreted as screen height (not the parent element)!
So long story short, if I use my S5 in portrait mode, the 1080×1920 screen makes the above SVG element 1920 pixels high, with 1080×540 (2:1) diagram in the middle of huge white area. The bug is reported in 2012: https://bugs.webkit.org/show_bug.cgi?id=82489. This was supposedly already fixed, but seems the new version hasn’t trickled to my mobile OS yet. Thankfully, the fix is quite simple and does seem to work, just add max-height to the element:
<svg version="1.1" style="max-height: 100%" viewBox="0 0 200 100">
here are some primitives
I didn’t even need the width=”100%” because that seems to be the default. Doesn’t hurt, though. So, just sharing this for everyone, maybe Google will index this and help others in need.
Another short web coding tidbit for today. I’ve been working on a Bottle.py+SQLAlchemy based backend for a personal project, and found very little information on how to convert a SQLAlchemy Core resultset into JSON.
Here is a glimpse into what was most commonly suggested. Tons of code. But wait, did you know you can cast a row into a
dict? No? Well, it makes a world of difference:
# somewhere here, accounts table is defined with SQLAlchemy syntax
res = conn.execute(select([accounts]))
# return all rows as a JSON array of objects
return json.dumps([dict(r) for r in res])
Now, which do you prefer, the last line or the longer 17-lines in StackOverflow? There is a slight problem though, namely date and numeric(x,y) fields, as they will turn into
decimal.Decimal types. Thankfully, Python’s JSON library can be provided with a function to handle classes that the library itself doesn’t handle:
import decimal, datetime
"""JSON encoder function for SQLAlchemy special classes."""
if isinstance(obj, datetime.date):
elif isinstance(obj, decimal.Decimal):
res = conn.execute(select([accounts]))
# use special handler for dates and decimals
return json.dumps([dict(r) for r in res], default=alchemyencoder)
I’ve had a small problem over a year: I have two headphone amplifiers, a transistor-based O2 headphone amp, and a tube-based Little Dot MKII. I also have two sets of headsets. Because switching the cables all the time is somewhat tedious, I haven’t really used the other amp and headphone set.
There are several Y switches that you can buy, but most seemed either expensive or mostly tailored towards electric guitar enthusiasts. And I would still need to combine two Y switches to toggle between the two amps and headphones. As the construction is really simple, I decided to solder my own. Here’s a short tutorial on how to make one yourself. You’ll need:
- 4 audio connectors (I chose 3.5mm over RCA), two to each end
- 2 switches with at least 3 connectors (left, right, ground) – I chose two 4 way switches
- A box where you can drill holes for the connectors and switches
- Small length of wire, some solder and soldering iron
1. The Schematic
The design of the switch is extremely simple. In both ends, three wires come from each of the two connectors to a switch, and the switches are connected to each other. I chose not to combine any ground lines to avoid ground loops. You need also to select a switch which breaks the connection on one side before connecting the other so the amplifiers will not feed into each other.
2. Soldering the wires
Despite the simple construction, there is a lot of soldering involved. Each of the four connectors will have ground plus left and right channels, and all have the switch on the other end. That makes 24 solder points (4x3x2), and there’s six more between the switches for a total of 30 points. The 3.5mm connectors had small “L” and “R” markings to tell which channel is left and which is right. I used different colors of wires for each type to avoid mixing L, R and ground.
Continue reading Simple X Audio Switch (Double-Y)