DIY Bluetooth Keyboard Breakout for $10

You could get an excellent Bluetooth keyboard controller from Adafruit called Bluefruit EZ-Key which allowed super easy creation of projects that sent keyboard presses (for example a gamepad) just by connecting some switches to the pins. However, the EZ-Key cost $20 and is now discontinued. And in any case, Bluetooth-capable devboards are now available from AliExpress for a few dollars, so $20 today feels on the steep side. “Could it be done cheaper?” I wondered…

I have honestly about a dozen cheap wireless devboards lying around, many based on ESP8266 which only have Wi-Fi, but some also with ESP32 which includes Bluetooth. I spent some time trying to configure a Chinese ZS-040 serial Bluetooth module to function as a keyboard, but the AT command set was a very small subset of what the similar HC-05 / HC-06 modules have. After an evening of trying, I decided to give up on that. There are instructions how to flash HC-05 modules with RN-42 firmware to get Bluetooth HID capability, but it will require quite a few steps.

I also took a look at esp32_mouse_keyboard project, but for some reason or another, abandoned that avenue. Don’t recall if there were obstacles or the project was still incomplete a year ago, might also be that the ESP32 only had BT LE which technically didn’t support HID (Human Interface Device). Throw me a comment if you have that working!

Meanwhile, another idea dawned to me:

A Cheap Bluetooth Keyboard Must Contain A Bluetooth Module

Enter the wonders of AliExpress: While you cannot source an easy BT keyboard module from US under $20, you can get a full mini Bluetooth keyboard for $9.50 (at time of writing) including postage! This package ought to contain:

  • A fully compliant Bluetooth board that pairs with iOS, Android and PC devices
  • Full functioning keyboard and case
  • Presumably, a battery and a way to charge it

Sounds a too good deal to be true? Well, let’s find out! The keyboard has a solid metal backplate that is easily screwed open with micro cross head screwdriver. Once inside, it reveals a very professional layout with a flat ribbon cable (or “FCC cable”) coming from the mechanical part into the controller module, And a small (most likely LiPo) battery.

Taking the tape off and turning the board around reveals a bit spacious, but very professional looking PCB with clear markings. There are easily usable on/off switch and connect button on the PCB, a connector for the keyboard switches, and obviously some kind of microcontroller wired to the connector, as well as another smaller chip that is most likely a voltage regulator or charging chip.

I Googled around to find out if the “YC1026” MCU would have a datasheet to help me along the way, but unfortunately I only got Chinese web pages (most likely the manufacturer) without any documentation. Time to dig out my trusty Picotech 2000 scope and do some old-fashioned reverse engineering!
Continue reading DIY Bluetooth Keyboard Breakout for $10

$8 Bluetooth automation button for Raspberry Pi Zero W

This project was born as a sidetrack of another one (I’m planning on building a $10 DIY Bluetooth page turning pedal for my piano and iPad sheet music app, similar to PageFlip Butterfly). I was looking if AliExpress would have bluetooth pedals, which they don’t — it seems Chinese vendors are REALLY good at copying products but there is little new product innovation combining something as simple as a bluetooth keyboard sending one or two keys with a pedal (two items that they do have)! But while searching, I found this inexpensive gadget (in case the product is removed, you might just search for “bluetooth remote” at AliExpress.com):

So what is it? It’s an $8 disc with multimedia buttons that pairs with your smartphone and you can use it for example in car to control your music. But maybe it would pair with my Raspberry Pi W which has integrated bluetooth as well? Well it costs about nothing to find out!

Fast forward about two weeks and it arrived. I did not try to use it for its intended purpose, but instead went straight to pair it with my Raspberry Pi Zero W. Turns out the pairing process was quite painless, you can follow for example LifeHacker’s tutorial for pairing quite easily. And it goes a little something like this (your MAC address might vary, just look for output after “scan on”):

# bluetoothctl
power on
agent on
scan on
connect FF:FF:00:45:8D:FF
trust FF:FF:00:45:8D:FF

Continue reading $8 Bluetooth automation button for Raspberry Pi Zero W

Hands-on review of IKALOGIC SQ200

Most electronics DIY projects I’ve worked in the past have involved digital communication protocols such as USB, UART or PS/2. Sometimes when first twiddling with a new protocols, everything works nicely. Other times, things don’t quite work the way they should. In the latter case, a logic analyzer is an invaluable tool, essentially a multi-channel logger of digital signals, which you can use to hopefully pinpoint where things are not going as they should. Nowadays most of these are connected to PC, so you can capture a piece of communications between two devices, and analyze what is happening with a dedicated software.

I started my logic analysis with the inexpensive Bus Pirate, but after a while also got Saleae Logic unit I used to view the PS/2 traffic in my knock sensor project. Later on, I have gotten the PicoScope 2208B which has both analog oscilloscope functionality, as well as digital logic analysis capabilities.

So when I was contacted by IKALOGIC, the makers of ScanaQuad series of logic analyzers, who offered to send me a unit to try out in return for a review, I though I was in a good position to give it a spin and also have previous experience to compare it against. I also had a project in mind to test drive the SQ200 unit I got: my recent MIDI-USB adapter, which is a combination of slow 32 KHz serial signals, and quite fast USB signalling.

Note: I received the review unit from Ikalogic without cost, but with freedom to form my own opinion about the device. I’m giving praise where it’s due, but not pulling any punches where something will nag me or compare unfavorably against the devices I’ve had first-hand experience in the past!

Unboxing the ScanaQuad SQ200

The unit arrived well packaged, and inside the plastic wrapping I uncovered a matte black cardboard box with the unit name. A grade above no-name Chinese vendors, but of course not an iPhone “unwrapping ceremony” kind of thing either. Inside, there was the unit, USB cord and logic probes neatly packed (click for larger images).

There’s nothing complicated in taking the unit into use: Just attach the USB cable, the probes, and you’re set. Build quality of the unit is very good, with grey matte surface with nice finishing, four screws and a product spec sticker on the backside, and logo, markings and a power/activity LED on top.

Size-wise, the SQ200 is slightly larger than the very compact Logic unit I have from Saleae (it’s an old model, don’t recall the exact model code), which I rate as the gold standard in product casing, with Apple-esque metal feel (aluminum?) and solid construction. The Saleae unit actually has 8 channels despite it’s smaller size. On the comparison image you can also see PicoScope 2208B with 16-channel MSO capability. Compared to that, both IKALOGIC and Saleae units are quity tiny (still, the palm-sized 2208B is extremely compact as well, given the 2 high frequency analog channels and waveform generator).


Continue reading Hands-on review of IKALOGIC SQ200

$5 USB MIDI adapter with ATmega32u4

This article will detail how to build a USB MIDI adapter (one-directional: you connect the adapter with USB cable to your computer, and it receives notes and pedal data from your keyboard’s MIDI OUT and transmits them to your computer) with ATmega32u4, 6N137 optocoupler, a few resistors and spare MIDI connector or cable. Read on for details!

Preamble

Last year I wrote how you can turn Teensy LC into an inexpensive USB MIDI adapter. I used it to replace a non-working Chinese MIDI-USB adapter that did not send controller messages (i.e. piano pedal) properly to PC.

However, since the Teensy still costs $12, and you have to get some additional components, it doesn’t make sense to use it in a dedicated MIDI adapter, since you can get a working USB MIDI adapter for around $15 from Thomann and probably many other places.

But how about other boards? After making my Teensy LC adapter, I actually tinkered with Adafruit Pro Trinket, and got that working as well (the standard Trinket does not have hardware UART so V-USB and software UART is somewhat risky). But there is even a better board for this: The ATmega32u4 board I previously showed how it can be made into USB HID mouse. Let’s see how to turn it into a USB MIDI adapter!

Required hardware

To build this, you will need roughly $5.40 worth of components:

  • SparkFun Pro Micro (clones with ATmega32u4 can be had for $3.50 from AliExpress, eBay, etc.)
  • 6N137 optocoupler, which can be had for ~$0.30 a piece (I suggest sourcing a couple in case you burn one by accident)
  • 330 ohm and 2 kohm resistors ($0.10) and 1N4148 diode if you want to be safe
  • MIDI connector or alternatively you can just cut a short cheap MIDI cable and wire it to your project, let’s say $1.50

Continue reading $5 USB MIDI adapter with ATmega32u4

Split MIDI Files with Python

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:

  1. Keeps tab on keys and pedals pressed
  2. Whenever X seconds elapse without any keys or pedals down, a new MIDI file is started
  3. 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:

pi@raspberrypi:~ $ git clone https://github.com/craigsapp/midifile
pi@raspberrypi:~ $ cd midifile
pi@raspberrypi:~/midifile $ make

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):

"MThd"
4'6
2'0
2'1
2'384

;;; TRACK 0 ----------------------------------
"MTrk"
4'50044
v0      ff 51 v3 t120
v0      ff 58 v4 '4 '2 '24 '8
v7147   90 '58 '29
v88     b0 '64 '5
v1      b0 '64 '7

[LOTS OF MIDI EVENTS]

v0      ff 2f v0

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:
Continue reading Split MIDI Files with Python

Using Raspberry Pi as an automatic MIDI logger

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!

Update: Also check out my follow-up post to split the recorded MIDI files automatically!

Recording MIDI with Raspbian

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

Continue reading Using Raspberry Pi as an automatic MIDI logger

Picoscope 2208B MSO Review

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 various projects. 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
Continue reading Picoscope 2208B MSO Review

New Picotech 2208B Unboxing Video!

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!

IR signal recorder with Arduino Uno

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:
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BeagleBone Black GPIO Benchmark

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:

  BeagleBone Black Raspberry Pi 2 (B)
Price 46 € (Element14) 32 € (Element14)
Processor 1GHz single-core Cortex-A8 0.9GHz quad-core Cortex-A7
Memory 512MB DDR3 1GB
Connections USB host, USB device, micro-HDMI 4x USB, HDMI, 3.5mm Audio/analog video
GPIO 2x 46 pin headers (65 digital I/O) 40 GPIO pins (26 digital I/O)
Other 4GB integrated flash, works as USB device camera and display interface on board

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

Test bench

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).
Continue reading BeagleBone Black GPIO Benchmark