In my previous post I showed how to use Raspberry Pi to automatically record MIDI files from digital piano whenever you turn it on. However, if you sit down and play for an hour, and get one big MIDI file, it is not very useful. So what to do?
Pianoteq has a feature that splits your playing session based on breaks you take between playing notes. So I decided to mimick this feature with a simple Python script that:
Keeps tab on keys and pedals pressed
Whenever X seconds elapse without any keys or pedals down, a new MIDI file is started
Additionally, if user presses and releases sustain pedal several times in the end, filename for that MIDI is altered to “highlight” that file
I first thought to learn enough of MIDI file format to do everything from scratch, but there’s quite a bit of small details to handle, so in the end I decided to use an external toolkit from Craig Stuart Sapp called midifile to do the heavy lifting. You should be able to just clone the Git repo and make it with Raspberry Pi:
You should now have two useful commands in ~/midifile/bin: toascii to read a MIDI file and dump an ASCII (text) version of it, and tobinary to do the reverse. With Python’s Popen and smart piping, we can read and write the binary MIDI files as they were in this text format. You can check out how the format looks like with some MIDI file you have:
~/midifile/bin/toascii somemidi.mid | less
Here’s a sample of a MIDI file recorded by arecordmidi (I added the note in square brackets):
There’s some header data in the beginning, and each MIDI event is comprised of a deltatime field starting with ‘v’, and then fairly standard MIDI events in straightforward syntax. I hardcoded my program to expect single track which starts with tempo and speed data (ff 51 and ff 58 lines) which I use to calculate how many deltatime units is one second. I copy this header part to start of every MIDI file, and append the final “ff 2f v0” (END TRACK) event to the end. Here’s the full code:
During my summer holidays I got an interesting idea: Pianoteq has a very nice feature of “always on MIDI logging” that saves everything you play on your keyboard while Pianoteq was on. I’ve previously made some MIDI projects and had a great idea:
How about building a small device that records everything I play on my piano, and save it as MIDI files?
This would enable me to later grab a good performance, and eliminate the “recording anxiety” I get if I know I’m recording and should definitely not do any mistakes during the next 1000+ notes. Furthermore, even with easy MIDI recording to USB stick, it’s still several manual steps plugging the memory stick in, starting recording, stopping it, lugging it to a computer, etc.
My first idea was to use some WLAN-enabled embedded device, but MIDI IN would require optoisolators and some custom electronics, and more modern digital pianos often come with only USB MIDI, so it could easily become an exercise in communication protocols. Fast forward a couple of minutes to my next revelation:
Raspberry Pi Model 0 W already has USB and WLAN, and it’s small. Why not use that?
Turns out using a RaspPi as fully automated MIDI logger is really easy. Read on for instructions!
Turns out recording MIDI from a USB MIDI enabled device is really easy. When I plug in my Kawai CS-11 (sorry for the unsolicited link, I love my CS11 :) to the Pi (or just turn it on when it’s plugged in), dmesg shows that the Pi automatically notices the new MIDI device:
[ 587.887059] usb 1-1.5: new full-speed USB device number 4 using dwc_otg
[ 588.022788] usb 1-1.5: New USB device found, idVendor=0f54, idProduct=0101
[ 588.022800] usb 1-1.5: New USB device strings: Mfr=0, Product=2, SerialNumber=0
[ 588.022807] usb 1-1.5: Product: USB-MIDI
[ 588.074579] usbcore: registered new interface driver snd-usb-audio
Once the USB MIDI device is found, you can use arecordmidi -l to list available MIDI ports:
pi@raspberrypi:~ $ arecordmidi -l
Port Client name Port name
14:0 Midi Through Midi Through Port-0
20:0 USB-MIDI USB-MIDI MIDI 1
There are few tools that are essential for an electronics hobbyist. When I started, I had a soldering iron, a multimeter and some components, and that was about it. That got me quite far because you can do simple debugging even with a multimeter, but once you start to do any communications, you will either work in the dark or get a signal analyzer, oscilloscope, or both. I reached that point about 9 months into my hobby, and eventually decided to get an entry-level PicoScope from Picotech. You can read the whole story from my PicoScope 2204 review from four years ago.
Long story short, I was extremely happy with my Picoscope, and I’ve been using Picotech’s products ever since in variousprojects. In the past years, I’ve also been collaborating with Picotech, so I’ve had the chance to use also their higher end models, including the frighteningly powerful 4-channel, 200 MHz, 16 bit PicoScope 5444B, which is really great but maybe even too hefty for my use. So when I was offered the chance to try out Picotech’s latest generation of their entry-level 2000 series published just a month ago, I was immediately in.
Without further ado, let’s get reviewing!
PicoScope 2000 series overview
The new PicoScope 2000 series is divided into roughly two groups of equipment: The entry models 2204 and 2205 range in price from 139€ for the 10 MHz 2-channel 2204A to 419€ 2205A and 2405A which are 25 MHz and have MSO (mixed-signal oscilloscope, i.e. it has 16 channel digital part as well) capability and 4-channels, respectively. Don’t let the low bandwith confuse you, even these models have sampling rates ranging from 100 MS/s to 500 MS/s, so you will get quite a lot of measuring power out of them.
Biggest limitation with 2204 and 2205 models is the buffer size, which ranges from 8 kS to 48 kS, so for longer captures than a few waveforms, only option is the continuous capture over USB which worked at a steady rate of 1 MS/s the last time I used it. So you can do unlimited capturing of signals around 100 kHz, but above that it’s the normal oscilloscope triggering business — that’s the way scopes have always worked from their beginnings, so it gets the job done as well.
2204
2205
2206
2207
2208
Bandwith
10 MHz
20 MHz
50 MHz
70 MHz
100 MHz
Sample rate
100 MS/s
200 MS/s
500 MS/s
1000 MS/s
1000 MS/s
Resolution *
8 bit
8 bit
8 bit
8 bit
8 bit
Memory
8 kS
16 kS (48 kS w. MSO/4ch)
32 MS
64 MS
128 MS
Price (2015-22-05)
139 €
209 €
319 €
459 €
629 €
Options
–
MSO or 4ch
MSO or 4ch
MSO or 4ch
MSO or 4ch
*) Resolution for repeating signals can be increased to 12 bit with multiple samples
Picotech launched a new set of very compact but powerful 2000 series oscilloscopes just a few weeks ago, and with my long-term collaboration with them (they really rock :) they were kind enough to send me a unit for reviewing! The review will hopefully come quite soon, but meanwhile, enjoy this amazing unboxing video. And with “amazing”, I mean “I did not completely fail the lighting and achieved 90 % intelligible pronunciation”.
The unit in question is the high-spec 100 MHz 2208B with 16 channel logic analyzer unit built in. I knew that this replacement line to the old light blue 2000 series scopes was small, but I was still amazed by the compactness of this beast. Having had a top end 5000 series Picoscope for a few years, I’m seriously considering the “downgrade”, as I mostly use just one or two channels of the scope, and even those are in many cases digital signals. But I’ll return to this in the review later.
Let me know what you think, either here on in the Youtube comments section!
I’ve been tinkering with IR and the TSOP38238 IR receiver modules I got from Adafruit and Sparkfun. That’s right, plural, as I burned the first one — be REALLY sure not to mix ground and VCC with this one! I ordered 10 more from AliExpress just to make sure I have spares in case I burn my second one as well…
There are IR libraries for Arduino already, but they were a bit complex to my taste, as I’m first planning just to record one IR code from my bulky Sony projector remote and make a small trinket to send that on button press. The TSOP382 already demodulates the signal, so I just want to record the times the remote IR led is on, off, on, off, and so on. So I made an Arduino sketch to do just that: Count loop cycles, detect when signal goes from high (no IR signal detected) to low and vice versa:
Look what the mailman brought: It’s a shiny (or maybe matte?) BeagleBone Black, freshly arrived (actually it’s been over a month, but time sure flies…) from Newark element14! I’ve been doing Raspberry Pi related hacking for a while, but especially when the Pi was still fresh and new, I did from time to time consider if the grass would be greener on other side of the fence. Or blacker, in this case, as I mean BeagleBone Black.
BeagleBone was long very much more powerful than Raspberry Pi, but now that Pi2 has come out, price and specification-wise they are closer than ever. A quick personal comparison chart:
When Pi1 was out, the BeagleBone Black with the more modern Cortex-A8 chip and higher clockrate was definitely the more powerful, but now with 4-core Pi2, the tables have somewhat turned. Still, the clockrate is higher and there’s more GPIO. And speaking of GPIO, my Raspberry Pi vs. Pi2 GPIO benchmark has gotten a lot of interest, so I thought the best way to take this black beauty for a test drive would be to benchmark BeagleBone Black GPIO in a similar way.
Test setup
The test subject is the most recent revision C of BeagleBone Black. I followed the (a bit lacking in detail and readability) Getting Started guide and downloaded the latest Debian Jessie image (8.3, 2016-01-24), flashed it to card and ran apt-get update and apt-get dist-upgrade (2016-04-14).
