Tuning up a littleBits oscillator

I’m starting to experiment with the littleBits oscillator and synth bits. I’d like to control the oscillators using an Arturia Keystep either through MIDI or through the Keystep’s control voltage (CV) and gate outputs.

Perusing the littleBits forum, I noticed several complaints about how difficult the oscillators are to tune. Setting the basic pitch is not a problem — just turn the PITCH knob. The issue is really intonation. Guitarists are very familiar with intonation, that is, being in tune along the fretboard. The keyboard equivalent is being in tune across the entire keyboard or a given range of keys.

For my initial testing, I assembled a simple littleBits circuit:

Power -> MIDI module -> Oscillator -> Dimmer -> Synth Speaker

The littleBits MIDI module was connected to an Arturia Keystep and for comparison’s sake, a Korg MicroKORG. The MIDI module translates incoming MIDI note on and note off messages into littleBits-compatible CV. The Dimmer is the volume control. I find it much easier to set volume levels, etc. with a full-size pot instead of a trimmer. Also, I strongly recommend putting knobs on the oscillator PITCH pot. It is much easier to set the oscillator pitch accurately when a knob is installed. (Funny how the little things make a big difference.)

My first concern was the actual control voltage being sent to the oscillator. I pulled out my trusty multimeter and measured the Keystep’s pitch (CV) over a wide range of keys (notes). I also measured the CV generated by the littleBits w5 MIDI module. The voltages all look reasonable for 1 volt per octave CV, modulo the limited 3 digit precision of the multimeter. Two notes separated by an octave produced a one Volt difference as expected.

The Keystep generates CV from 0 Volts to 10 Volts. littleBits signals are limited to the range from 0 Volts to 5 Volts. Rather than tempt fate and drive the littleBits oscillator from the Keystep CV output, I decided to put a littleBits CV interface module on order. The CV interface scales CV to the littleBits range — whatever that means. Stay tuned.

The voltage for each note as produced by each CV source (Keystep CV vs. MIDI module) is not the same. For example, the Keystep generates 4.03 Volts for MIDI note C2 while the MIDI module generates 1.20 Volts. Relax. This isn’t a big deal as the basic pitch is easily set by the oscillator’s PITCH control. It’s all relative, man.

I used a Snark guitar tuner to set the pitch and to test intonation. The Snark is an inexpensive small tuner with a microphone input. I like the Snark because it shows the detected note (C, C#, D, etc.) and whether the note is flat or sharp. I don’t like the Snark because the clip-on thingy breaks off almost immediately! The clip-on thingy isn’t necessary for desktop testing, however.

I first tried setting the pitch and intonation by ear. This is where the MicroKORG was really handy. I sent the MicroKORG’s MIDI out to the MIDI-to-CV module and routed the MicroKORG’s audio output to the mixer feeding the studio monitors. I also patched the littleBits audio into the mixer, so I could easily dial up the MicroKorg audio as a pitch reference. Hit a single key on the MicroKORG and both the oscillator and MicroKORG attempt to play the same note. Adjust the PITCH and TUNE knobs appropriately.

The Snark tuner method is much better. The Snark’s display shows when things are sharp or flat. I recommend using a tuner like the Snark instead of matching pitch by ear.

At first I couldn’t get satisfactory intonation beyond a one octave range. This is disappointing and appears to be the place where most forum members gave up. I read the Korg littleBits Synth booklet paying particular attention to the tuning procedure on page 21. One of my biggest complaints about the littleBits system is the lack of detailed documentation and the Synth book was kind of sketchy about tuning and intonation. However, a light did turn on in my head.

I decided to turn the TUNE trimmer fully clockwise (thinking “OFF”). Then, I set the base pitch, i.e., the lowest pitch in the desired range. Next, I checked the highest note in the desired range — about two octaves. Natch, the intonation was bad, so I slowly turned the TUNE trimmer clockwise until the pitch of the highest note was correct. This disturbed the pitch of the lowest note and I had to find a balance between pitchiness at the low and high ends.

The result is fairly playable. I played the chromatic scale from lowest to highest and checked the Snark at each step. The intonation was acceptable.

To make sure this procedure wasn’t a fluke, I tuned the second oscillator using the same method and got the same result. Finally, I wired up the MIDI module driving both oscillators and mixed the audio:

                             |-> Osc ->|
Power -> MIDI -> Split ->|         |-> Mix -> Dimmer -> Speaker
                             |-> Osc ->|

The pitches were danged close and the intonation of the individual oscillators matched quite well. I just needed to adjust the relative tuning to get a good phat sound.

Not bad for “cheap” $16 USD oscillators! It’s rather unfair to blame the oscillator design at this price. Plus, you did say that you want analog synthesis, right? We’ve gotten spoiled by decades of pitch-perfect digital synths. Making the tuning and intonation right is all part of the analog game.

One final thought. The littleBits CV signal driving the oscillators is somewhat under-documented. Voltage Control Lab have a nice analysis. They explain the littleBits OUT signal from the Korg SQ-1. They say that the CV signal plays two roles as a combined gate and pitch control. When the CV is asserted, i.e., the gate is high, the voltage level sets the pitch.

Here’s a more MIDI-centric interpretation. When a MIDI note is off, the CV signal is 0 Volts. The oscillator is silent at 0 Volts. When a MIDI note is on and held, the CV signal sets the pitch. When the MIDI note goes off, the CV signal returns to 0 Volts and silences the oscillator. This appears to be the behavior of the MIDI module (when it is in MIDI IN mode).

The Arduino combo organ is back

If you have a taste for cheesy 1960s combo organ sounds, I just posted the littleBits MIDI organ project. This project is an updated littleBits take on my old Combo Organ project. It uses the same “bottom octave generator” technique to squeeze five sample playback voices out of an Arduino.

Here’s an MP3 demo of the Farfisa voice and a demo of the Vox voice. I drove the MIDI organ from SONAR on a PC.

Here’s why you should prefer the littleBits version. The original project uses the MidiVox shield which is out of production. The littleBits version replaces the MidiVox with two breadboard-based circuits: a MIDI input interface and a Small Peripheral Interface (SPI) digital-to-analog converter (DAC). Easy to build and functionally equivalent. The new sketch incorporates improvements made to the Arduino SPI library and PROGMEM. The current SPI library uses a different convention for sending data to the DAC. PROGMEM is way different now; the old code won’t compile. The newer version of PROGMEM is stricter about typing and const.

The littleBits MIDI organ could form the basis of a sample playback synthesizer. Just replace the Farfisa and Vox waveforms with single cycle samples of your favorite synth or retro keyboard. Waveform space in PROGMEM is still tight, but hey, this is science. It’s supposed to be fun!

You’ll need to add a few headers to the littleBits Arduino module in order to use SPI. Here are some simple directions and tips:

Add SPI to littleBits Arduino Part 1
Add SPI to littleBits Arduino Part 2
Add SPI to littleBits Arduino Part 3

You’ll also find the SPI DAC and MIDI interface designs in parts 2 and 3, respectively.

While you’re at the littleBits site, check out f.j2’s Solina string synthesizer. Retro is bustin’ out all over!

I need to switch gears for a little while and be a musician again. So, I’ll be taking a short break from Arduino projects. More to come on the music side of things…

Sing “Do Re Mi” using an Arduino SPI DAC

After a few months away from electronics, I dusted off the littleBits Arduino project that I completed way back in September. Just as I completed the project, we took a short vacation trip — just enough time away to break the creative flow and to procrastinate about a write-up.

The old-new project uses the Arduino SPI digital-to-analog converter which I sketched out in two earlier posts: How to add SPI to a littleBits Arduino and the Arduino SPI DAC design. The SPI DAC greatly improves audio quality over the el-cheapo PWM+filter approach. It adds a little extra hardware, but it’s worth it.

The SPI DAC project adds a 12-bit digital-to-analog converter (DAC) to the littleBits Arduino. The DAC is a Microchips Technology MCP4921. The design is fairly simple and could be whipped together by a novice. I built the circuit on a solderless breadboard in order to avoid soldering. You still need to solder a 2×3 header to the littleBits Arduino. Can’t avoid it unless littleBits decides to sell Arduino modules with pre-installed headers.

I wanted to make the project “kid friendly.” So, rather than geeking out with MIDI, synthesis, etc., the sketch sings a song in Solege (i.e., “Do, re, mi). The Arduino’s program memory (PROGMEM) holds the waveforms (samples) for the eight syllables of the C major scale. The song is represented in an array where each row of the array contains the pitch and duration of a note. The sketch steps through the song array and sings each note (a Solfege syllable). Check out the MP3 demo.

As you might guess, it took a fair bit of effort to fit the waveforms into 28K bytes of PROGMEM! For more information, read about the waveform development process.

I posted the full design and code on the littleBits web site. I want to move ahead to new projects and frontiers and I won’t be posting the detailed design here. I do want to use the SPI DAC in future projects.

While you’re at the littleBits site, please check out the Mini Pops Drumcomputer. This is a very nice update on the Lo-fi Beat Box project. The developer, f.j2, fabricated the low pass filter as a littleBits module using the littleBits Hardware Development Kit (HDK). He also added new waveforms. Great job!

Arduino lo-fi beat box

Here’s another Arduino-based music project for ya — the Beat Box — a lo-fi, TR-808 drum machine. If you ever wanted to try your hand at DIY electronics, this one is a good starting point. Here is a short list of features:

  • 16 grungy, TR808-like rhythm instruments
  • Up to eight instruments per pattern
  • Up to five selectable patterns
  • Adjustable tempo (60 BPM to 188 BPM)
  • Full source code available including waveforms (samples)
  • Write and compile your own patterns, drum kits and waveforms
  • Built-in PWM signal generation into an external low pass filter
  • 22,050Hz, 8-bit signed, mono waveforms for true lo-fi grunge

The Beat Box uses the Arduino’s internal high resolution timer (TIMER1) to produce audio. The timer converts samples to a pulse-width modulated (PWM) bit stream which is sent into a simple low pass filter. The filter converts the PWM bit stream into an audio signal to be sent to a powered speaker, LINE IN, or what have you. This is absolutely the cheapest way to generate digital audio with an Arduino and it only requires four simple components, a solderless breadboard and a few jumper wires.

If you want to make assembly even easier, start with the littleBits Arduino Coding Kit, a Proto module and a Synth Speaker Module. I built the Beat Box using the littleBits Arduino Coding Hit and assembly was, literally, a snap.

The Beat Box source code includes drum waveforms and several classic drum patterns. With a 22,050Hz sampling rate and 8-bit samples, you get genuine lo-fi, bit-crunched TR-808 grunge. Purely optional, I added a littleBits synth Filter module and Delay module to the audio signal chain. Listen to the MP3 demo. In the demo, I sweep the filter frequency from low to open. At about 10 seconds in, you hear what is essentially the unfiltered sound of the Beat Box. Then, I increase the delay feedback level which adds echoes in time with the original pattern.

This pattern forever reminds me of riding the RTA #48 bus to work in Cleveland circa 1982.

Per standard operating procedure, I have provided the full design and source code.

Get your beat on! Build it now!

Connect a MIDI shield to littleBits Arduino

My do-it-yourself MIDI interface for littleBits Arduino probably isn’t for everyone. Constructing the DIY interface requires circuit layout skills and not everyone wants to whip up a board from scratch and a schematic.

Fortunately, there are a couple of alternatives: the Olimex SHIELD-MIDI and the Sparkfun MIDI Shield. I don’t have any direct experience with the Olimex, but I have built and used the Sparkfun MIDI Shield (Sparkfun product number DEV-12898) and the now retired MIDI Breakout Board. The Olimex SHIELD-MIDI is very similar to the retired breakout board. In this post, I show how to hookup the Sparkfun MIDI Breakout Board to the littleBits Arduino. The wiring is the same for the Sparkfun MIDI Shield. That’s the neat thing about the standard Arduino form factor.

I would demonstrate with a Sparkfun MIDI Shield, but all of my MIDI Shields are customized in some way! The Sparkfun MIDI Breakout Board is basically the same as the MIDI Shield except that it doesn’t have the potentiometers and tactile switches. The image below is a picture of the Sparkfun MIDI Breakout board. (Click on the image to get higher resolution.) The two 5-pin DIN connectors are the MIDI IN and MIDI OUT ports. The long pins extending below the breakout board plug into a standard Arduino like an UNO or Leonardo.

sparkfun_midi_breakout

The Sparkfun MIDI breakout board (or shield) arrives as a kit, so you still need to do some assembly. Sparkfun has already installed and soldered the tough stuff like the optoisolator, resistors and so forth. The MIDI Shield is a good beginner’s kit because the components to be installed are large and easy to solder. If you skip installing the potentiometers and tactile switches, the job is even easier!

You might want to add an Arduino Stackable Header Kit (PRT-10007), however. With the header kit, you’ll be able to interconnect using standard jumper wires. Once the headers are installed, no further soldering is necessary. Just plug the jumpers into the headers and play. Mistakes are easier to correct with jumper wires, too.

Here is the top-view of the MIDI breakout board, an Arduino UNO processor board and a Sparkfun MIDI Shield. Click the image for higher resolution. You’ll want to take a closer look at the three boards in order to see the signal name associated with each header pin. (You can really zoom in if you download the image and load it into a paint program.)

midi_bob_uno_shield

The breakout board has a position for a MIDI THRU connector. This position is empty as the headers would block the opening of the 5-pin DIN connector. We don’t need the THRU port, so this isn’t a deal-breaker.

As I mentioned before, the long pins extending below the headers normally plug into a standard Arduino processor board (e.g., UNO or Leonardo). Each header pin effectively mirrors the electrical signals of the underlying Arduino board. So, in order to hookup to the littleBits Arduino, we just need to connect the appropriate Arduino board signals to the corresponding bitSnaps on the littleBits Arduino. That’s why you really want to zoom in and see the signal names. The board labels tell us where to plug in jumper wires.

We need four connections:

  • +5 Volts: Red wire
  • Ground: Black wire
  • RX (digital pin D0): Yellow wire
  • TX (digital pin D1): Blue wire

Our old high school shop teacher would yell at us if we didn’t use the right color wire for power, ground, etc. I will say, different wire colors make it easier to check and debug wiring!

So, how do we make connections to the littleBits Arduino? I used two littleBits proto modules: one proto module for the MIDI input side and one proto module for the MIDI output side. The other end of each jumper terminates in a screw connector on a proto module. Please see the image below. (Click to enlarge.)

sparkfun_midi_littlebits_arduino

RX is connected to RX, TX to TX, +5 Volts to +5 Volts, and Ground to Ground. The MIDI IN goes to the Arduino’s RX pin and the the Arduino’s TX pin goes to MIDI OUT.

You must configure the jumpers on each proto module. The MIDI OUT side is easy; just leave all three jumpers installed. One the MIDI IN side, remove the center jumper on the proto module. This breaks the connection from the proto board input to the proto board output. You must remove this jumper or the input signal will interfere with the incoming MIDI data.

Once all of the connections are made, you’ll need sketches to test the connections. Please see my article about testing an Arduino MIDI interface. The article describes a simple testing process. The article also has links to a simple MIDI sequencer sketch and the source code for a MIDI IN to MIDI OUT sketch. The MIDI sequencer sketch checks the MIDI OUT side. Once you know the MIDI OUT is good, then the MIDI IN to MIDI OUT sketch checks the MIDI IN side. (The sketch echoes MIDI IN to MIDI OUT.)

That’s it! You should now have your 5-pin MIDI equipment talking with the littleBits Arduino. If this project has bolstered your confidence with hardware — and I hope that it has — then please take a look at the DIY 5-pin MIDI interface project.

littleBits Arduino tone sequencer

The littleBits Arduino module has the potential to be a MIDI-driven tone generator for a mono or paraphonic synthesizer. After getting the module, I was anxious to try it out even though I haven’t built a MIDI interface for it (yet).

Here is a picture of the littleBits hardware. (Click the image to get full resolution.) The Arduino module is in the middle between the controls at the left (button and dimmers) and the synth speaker at the right. The controls on the left hand side don’t do anything at the moment. I put a dimmer between the output pin (D5) and the synth speaker in order to control audio volume. It’s just more convenient to control the volume with a dimmer than the tiny trim pot on the synth speaker module. The knobs on the dimmers are my own touch; they aren’t standard-issue with the littleBits dimmers.

arduino_dimmer_speaker

To keep things simple, I wrote a sketch that implements a basic note sequencer. Each note has a pitch (frequency) and a duration (milliseconds). The notes are stored in an array. The Arduino loop() function steps through the array of notes and plays one note at a time. After the loop plays the last note in the array, it goes back to the beginning of the array. The loop has a delay() in it and the loop keeps track of the remaining duration of the currently playing note. The sketch calls the Arduino tone() function to play notes by sending a square wave at the desired frequency to output pin D5.

If you would like to learn more about this project, then read about the design of this simple Arduino-based sequencer and tone generator. Here are links to the source code:

ToneTest.ino: Main sketch
ToneFreq.h: Note frequencies
ToneNote.h: Note durations

The D5 and D9 output pins on the littleBits Arduino module have a switch that enables or disables low pass filtering. The “analog” switch position turns on the filtering. The “pwm” position turns filtering off. Should you build this project yourself, try both switch positions. The “pwm” position doesn’t filter the square wave and you will hear it loud and nasty. The “analog” position produces a quieter, mellower timbre thanks to the low pass filter. Be sure to try the littleBits synth filter, envelope and delay modules, too.

One more tidbit. Pictures of the littleBits envelope, filter and delay modules usually show the top-view. The picture below flips the modules over and shows the bottom-view.

envelope_filter_delay

From left to right, the modules are the envelope, filter and delay, respectively. There is some serious electronics on these boards! (Click the image for full resolution.) I hope to use these modules to mangle audio, not just synthesis.

All the best.

Update: 28 June 2016. If you enjoyed this project and have the littleBits Synth Kit, then check out an expanded version of the tone sequencer which drives the filter and envelope modules.

littleBits Arduino: More observations

Back with a few more quick observations as I get started with the littleBits Arduino module. (Please see my first review.)

I decided to see how much stuff I could cram around the littleBits Arduino. (Click on the image below for full resolution.) This configuration starts with the power module on the left hand side. The power module is connected to a 9V 1500mA (1.5A) center positive power adapter with a 2.1mm plug. As I mentioned in my previous post, this is the same adapter that I use with my Arduino UNO. Already, I like the power switch on the power module — a very handy touch.

arduino_full_up

The power module drives three input modules (a button and two dimmers) via the fork module which is included in the Arduino Development Kit. The button module is connected to Arduino digital input D1 and the dimmer modules are connected to the Arduino analog inputs A0 and A1.

The Arduino D5 output is connected to a dimmer module that adjusts the volume (amplitude) of the signal sent to the synth speaker module. Yep, the synth speaker module has a volume control of its own. It’s that little trim pot in the lower left corner of speaker module. I find it difficult to adjust the tiny trim pot. Trim pots are designed for “set and forget” applications and have a limited rotational life (number of cycles). So, I splurged and inserted a dimmer module on the input to the speaker module.

I love the bargraph. You can use it as a poor man’s volt meter or logic indicator. I connected the bargraph module to Arduino output D9. Before I forget, the switches for D5 and D9 are set to the “analog” position.

I didn’t connect anything to Arduino digital output D1. A good first sketch would be blinking the on-board D1 LED on and off. So, I left the bitSnap empty.

The knobs on the dimmer modules are my own doing. The knobs do not come with the dimmer modules. I have a dozen or so of these basic knobs. The equivalent knobs are:

  • Multicomp CR-BA-7C6-180D ($0.35 per knob through MCM Electronics)
  • Sparkfun COM-08828 (now retired)

Knobs just make life easier and make things a little more dressed up.

I was hoping that littleBits had preloaded a sketch to the Arduino module and they did. The preloaded sketch makes the bargraph “breathe.” The sketch repeatedly ramps up the output voltage from zero volts to the MAX (5 volts) and ramps the voltage back down to zero volts. The dimmer connected to A1 controls the ramping speed, i.e., how fast the bargraph breathes.

I wish that littleBits made the preloaded sketch available on their web site. I couldn’t find it. Quite frequently, it’s handy to have a known-good sketch for testing purposes. I’m a stickler for testing and diagnostic programs. Too much emphasis on coding, not enough emphasis on testing, I say.

The littleBits site has a good introduction to installing and using the Arduino Integrated Development Environment (IDE). If you’re confused about the “analog” and “pwm” switch settings, be sure to scroll down into the comments section on this page. There is a good explanation. A short bit of advice: If you need to send an analog signal that varies anywhere from 0 to 5 volts, then put the switch into the “analog” position. If you need to send a purely digital signal (ON: 5V, OFF: 0V), then put the switch in the “pwm” position. (A pulse chain is, of course, a type of digital signal.)

If you’ve taken a look at the Arduino module schematic, you know that the switch enables (or disables) two extra stages of low pass filtering. The low pass filters (when enabled) generate an analog signal by smoothing out a PWM signal. This is essentially a poor man’s digital to analog converter (DAC) although it isn’t very hi-fi.

The littleBits web site has ten sketches to get you started. This part of their site could use a little polishing. First, I couldn’t find the source code for the sketches! At last, I realized that the link to a sketch is under the “ADDITIONAL FILES” section on the right hand side of the page — beneath the relatively huge “ADD ALL TO CART” button. Ah, sales before service. Beginning users may not realize that this is the link to the code. They may not know that the “ino” file extension refers to an Arduino IDE code file! Maybe kids are less confused than adults, but details like this could easily turn off a youngster who is lacking self-confidence.

The sketch file names are a little whack and don’t always directly refer to the section or page titles on the sketch web pages. Here is a correspondence table that I put together:

Example                     Source code file
--------------------------  ------------------------------
Blink                       blink.ino
Hold An On/Off State        buttonRead_stateChange.ino
Blink Speed Control         analogRead_digitalOutput.ino
LED Fading Effect           analogRead_analogOutput.ino
Servo Sequence Recorder     Sequence_Recorder_Starter.ino
DIY Etch A Sketch           etchasketch_arduino.ino
Analog Pong                 analog_pong_arduino.ino
DIY Computer Mouse          mouseMoveNClick.ino
Play A Melody               toneMelody.zip
Change The Pitch            tonePitchFollower.ino

Again, littleBits need to reduce the frustration barrier especially since kids are involved or teachers who have suddenly been assigned to computer science.

In my first review, I mentioned how mounting boards are essential for building mechanically robust and electrically reliable littleBits systems. Definitely true. However, littleBits still have room for improvement. The current mounting boards have quite a bit of flex in them and the pegs still pop out easily. I had a heck of a time getting the system (pictured above) to stay firmly put in the mounting board. It’s takes a lot of pressure to get a big system into a mounting board. I’m afraid that the pressure will weaken the board connections. Perhaps things will get better with practice or use…

If you’re interested in the backstory about the littleBits Arduino module, then read this article.

littleBits: First review

Some things are inevitable…

I taught undergraduate and graduate hardware design for many years. It was always a challenge to give students hands-on experience with digital logic circuits, especially for large-scale digital systems. Gosh, I could write several long blog posts that recount the various breadboarding, prototyping and simulation approaches that my students used in the lab. Along with the achievements came many horrors.

So, picking up littleBits was inevitable.

littleBits are so cute. Just in case you’ve been in an isolated cave, littleBits modules are small building blocks with magnetic “bitSnaps” at opposing ends. The magnetic bitSnaps sort the ports into inputs and outputs, and enforce an output-to-input connection rule. Each bitSnap carries the positive voltage rail, the ground rail and a signal. (Click images to get full resolution.)

dimmer_bargraph

The littleBits range covers basic digital logic and analog building blocks including audio. The Synth Kit — designed in collaboration with Korg — has perhaps done the most to promote widespread discovery and use of littleBits. The Synth Kit certainly placed littleBits in relatively non-traditional hands and sources, namely, musicians and musical instrument retailers. Before their recent bankruptcy proceedings, one could find individual ‘Bits in Radio Shack stores.

According to the manager of a local Radio Shack, the littleBits suffered a very high theft rate. Shame on anyone who unlawfully filched these!

Most retailers today (like Barnes and Noble bookstores) sell littleBits kits. The kits make it easier for people to get started and it reduces the number of separate SKUs at point-of-sale. With Radio Shack’s reorganization, these days, it is more difficult to buy individual modules a la carte. The littleBits on-line shop carries the full range, of course. Still, one rarely finds ‘Bits or kits at a discount.

The kits are also a little less easy to steal although a Barnes and Noble shopkeeper acknowledged high theft potential, too. Stop stealing!

One reason why people may feel entitled to boost littleBits with sticky fingers is their perceived expense. An LED at $7.95 may seem grossly overpriced. However, each individual module has at least two bitSnaps and there is value-added design and electronics on board. The LED module, for example, has a voltage protected input and a driver. In fact, all signals in the littleBits series are driven and normalized; that’s what makes them special. If all you want is a naked LED with two leads, then by all means pass up littleBits and try something else!

Signal standardization is what makes littleBits what they are. littleBits are very close to the plug-and-play electronic LEGO™ blocks that educators have wanted for a zillion years.

I decided to forego prepackaged kits and buy a la carte. The kits usually have modules which I probably won’t use and it just seems like a waste to buy them. That includes the Synth Kit, too. (Are you surprised?) I don’t have any interest in the tiny keyboard or the sequencer. I’m not that interested in the oscillators for that matter. I want to drive my synth and other experiments with Arduino. Thus, the only kit that I have purchased is the Arduino Coding Kit. Everything in this kit is quite useable with the exception of the servo module. (Although a Neil Young Whizzer would be a unique project!)

The littleBits Arduino board is a good example of value-added engineering. Sure, the Arduino ‘Bit doesn’t provide all of the ins and outs of a stock Arduino UNO, for example. However, the bitSnap signals are standardized with protection on the inputs and (switchable) low pass filters on the PWM outputs. The serial transmit (TX) and receive (RX) signals are made available through bitSnaps, making MIDI IN and OUT a future possibility. Programming is supported through either USB or ICSP. You’ll need to add header pins for ICSP, but if you’re using ICSP, you already ride tall in the saddle.

arduino_battery

I intend to whip up MIDI IN and MIDI OUT circuits using PROTO modules. I thought long and hard about the options. The Hardware Development Kit contains two PROTO modules, one PERF module and 12 bitSnaps (6 male, 6 female). I am not a fan of pad-per-hole perf board, so the PERF module is not that attractive to me. I much prefer “DIP style” prototyping boards that accomodate full size, through hole DIP ICs. This is sooooo much easier to solder. For similar reasons, I’m not sure that I want to fiddle around crafting circuit boards to conform to the bitSnaps. Overall, I will probably buy two PROTO modules a la carte.

The littleBits web site is a little sketchy on certain vital details:

  • The Arduino board USB port is a micro USB port.
  • The power module can be driven by a 9V, center positive, 2.1mm power adapter — the same as an Arduino UNO.
  • The power module can drive any input bitSnap (any port in a storm).
  • The Arduino IDE should be configured for the Leonardo board.

I don’t like hunting around for this kind of information and I especially do not want to watch videos to find it! In fact this information should be printed on the plastic purple baggy containing the Arduino board. (Also, the link to Arduino sketches on the current baggy is dead.)

Thank goodness that the Arduino Development Kit comes with two mounting boards. A mounting board holds a littleBits circuit in place and makes connections reliable. I whipped together a simple circuit without using a mounting board and the relatively heavy adapter cable kept pulling the power module away from the other boards. The bitSnap magnets are simply not that big and strong. Programming and using an Arduino module without a mounting board would be a nightmare.

So far, a favorable, somewhat vanilla review. Here’s a bit of my own value-added as a computer science educator.

When I first powered up the pulse module — a 555 timer-based circuit that generates a regular stream of digital pulses — I didn’t necessarily see a clock. I saw a token generator. I thought, “Given the current design of the logic elements, wouldn’t it be neat to build and visualize a one-hot state machine (controller)?” If each latch module had a built-in LED showing the state of the latch, this application would be a natural for littleBits.

Even better, why not bag synchronous control altogether and go asynchronous, self-timed?

Ivan E. Sutherland, Turing Award paper, Communications of the ACM, Volume 32, Number 6, June 1989, pages 720-738. And don’t forget everything written by Chuck Seitz, too!

This immediately raises the question of what we want students to learn from their experience with littleBits. I want students to learn that:

Electronic systems are inherently parallel.

Students need to be exposed to concurrency and parallelism before their minds are corrupted by the sequential, synchronous paradigm in conventional programming languages.

The other question that pops up is scalability. littleBits logic elements currently operate at the bit level. However, I’d love to have modules at the bus level such that students could build their own CPUs, GPUs, whatever. Plug-and-play busses are a tougher design challenge electrically and mechanically. One possible solution is to transmit data words serially from module to module. Pass the word size along with the data in order to simulate any (reasonable) bus width. littleBits could then keep the current bitSnap form factor.

Finally, I would like to mention the module technology that gave me a start in digital electronics: DEC Register Transfer Modules, also called the “PDP-16” or “RTMs.” RTMs use a flowchart-like notation for control design. This approach opened a whole world to me including ISP, Petri Nets and eventually dataflow computing. Most importantly, RTMs taught my 19 year-old mind that computation is fundamentally parallel and we should design for and exploit concurrency right from the get-go. Nico Habermann, God bless him, did the same in the sophomore programming course at C-MU. This point of view influenced my entire professional life!

If you would like to know more about RTMs, then read “Designing Computers and Digital Systems Using PDP-16 Register Transfer Modules,” by C. Gordon Bell, John Grason and Allen Newell, 1972. I was one of the first guinea pigs to use RTMs in the computer design course taught by John Grason. Thanks, John!

See also “The Description and Use of Register-Transfer Modules,” C. Gordon Bell, J.L. Eggbert, J. Grason, and P. Williams, IEEE Transactions on Computers, Volume C-21, Number 5, May 1972, pages 495-500.