Author: derrick

New Features:

• CC Recording – Record and loop CC messages just like notes
• Per-Loop MIDI Channel Assignment – Route recorded notes and CCs to different devices
• MIDI Passthrough
• Loops Now Saved with Presets – if you recorded something cool, you can save it
• See the full list of changes at the bottom of the Loopster GitHub Page

For instructions on installing the new firmware, download the manual above.

I’ve been working on this update for quite a while. First the issue was scope creep – I kept adding in new features that popped into my head. The second issue was testing all of this again. I refactored most of the code (again), which in addition to all of the new features, created bunch of new bugs to squash. I also battled memory issues – CircuitPython is not the most efficient, and the RP2040 does not have much “oomph”. Thankfully, a majority of these problems were solved by just changing the way that scales are generated – creating them all at once made for a very large list of lists which is not very RAM friendly. Now, it only generates them when selected.

If you want to see the entire list of changes, check out the Loopster 2 GitHub page.

For more background, see the original Loopster 2 post here.

The first version of the loopster can be found here. Changes from V1:

• SMD Components – can get it partially assembled at the factory
• RP2040 chip built into board – no more raspberry pi pico needed
• RGB LEDs for buttons for user feedback
• Full sized MIDI In and MIDI Out in addition to USB midi
• Button matrix to use fewer GPIOs
• Unused GPIOs broken out to headers
  • Add your own sliders / buttons
  • Control a strip of neopixels
  • Audio out via PWM
• Slanted case design

New Features:

• Arpeggiator – hold buttons and turn encoder
• Save / Load user presets
  • save scale, starting screen, arp settings, MIDI channel, etc.
• Quantize chords and loops
• MIDI In Sync
  • BPM
  • Start / stop messages
• Record MIDI In to loops / chords
• RGB LEDs for user feedback
  • Recording pad blinks red, etc.

The problems I aimed to solve with V2 were mainly:

Make it easier to produce: I sold 5 units and a handful of kits of V1 and realized that it took me too long to assemble everything. I intend to sell this one as well, and want it to be fairly inexpensive.

Better MIDI features: TRS MIDI is annoying and we all know it. I wanted to be able to plug this directly into a synth without worrying about grabbing the right converter cable (or buying a new one)

Figure Out MIDI In: could have done this with USB MIDI in the last version, but that didn’t sound as useful as DIN MIDI In. I wanted to plug a MIDI keyboard into the Loopster and use it to record some loops and chords.

Better User Interface: I could only do so much with the little screen, and on top of that, it was CPU intensive to update.

Design Process

I don’t feel like going into detail about everything, and you can find better tutorials elsewhere anyway. I’ll focus on specific things that I learned.

Schematic / PCB Design

I don’t have a ton of experience with PCB layout and design – pretty much just the projects you see on this website that involve it. I was nervous about stepping it up so hard by embedding the raspberry pi Pico circuit directly into the board, so I settled on designing just a clone of the RP2040 for practice. But then I thought nah, let’s do it live.

The Raspberry Pi Hardware Design document was super thorough and easy to follow. It uses very common components, all of which JLCPCB had in stock. I had never done anything this close to this complicated and it worked after just a few modifications which have since been fixed on the PCB – keeping track of MIDI pins is hard :/. Either the lesson is that I experienced a miracle, or that you shouldn’t be afraid to try the same, even if you are a beginner like me.

BUTTONS

My main criteria were:

• Satisfying to push (not mushy)
• Relatively quiet (no arcade buttons)

I settled on cherry-style keyswitches that are fairly linear (aka not the super clicky “blue” ones.

DIN MIDI

A lot of folks don’t use USB midi. The old design used mini TRS for a midi out solution, but had no midi in. I knew I wanted to use full sized DIN midi ports, in and out. I have never messed with midi in, but it wasn’t too difficult to figure out. This website is super helpful

I messed up the pins on the first try – it’s super easy to confuse the orientation. Thankfully it wasn’t a critical mistake and using little jumpers helped to fix it. this cheat sheet is the best.

SCREEN / NEOPIXELS

I wanted to add features to the loopster, but needed a better solution for a user interface. Doing more with the SSD1306 OLED screen was a non-starter, as it’s too slow to update can’t have 200ms pauses when sendn MIDI notes. I landed on Neopixels under each key, the select button, and the encoder. Neopixels are great because they only take up one GPIO pin, regardless of length. They are also dirt cheap and there are libraries for using them for everything at this point. I could use multiple colors to emphasize to the user what is going on (button flashing red = recording, etc.).

The neopixels seem to run fine on 3.3 volts – I have always done this without a problem so I wasn’t worried too much.

Hardware lessons

• Be careful about DIN MIDI Pinouts – whether you are looking at the male or female view matters
• Break out unused pins to a header on the side, cause why not
• Always use the “dumbest” pin possible when assigning inputs / peripherals to pins.
  • Try not to use a SPI pin if another digital pin with no special features is available
  • Don’t use analog pins for digital things unless you have to
• Put white silkscreen under LEDs to bounce light up

Software Lessons

• When using Python… use more classes. Even if it seems kinda dumb at the time.
• Use GitHub more. Adding enhancement requests / issues to my own repo was super helpful for documenting and tracking.
• Use a “globals” file or some file that can be imported everywhere to avoid dealing with circular dependencies.
• Resist the urge to optimize – I made bad design choices to save on performance, but who knows if it even would have mattered. Better to ignore until it’s a problem.
• Keep modularization in mind the whole time. I refactored like 3 separate times because things would get unmanageable due to me not considering that some things would need to be used elsewhere in the future.
• AI is kinda nice. I resisted using it for whatever reason, but it does a great job with writing small Python functions and documenting code. Things that you know how to do, but are not interesting and take more time than you’d like.
• The last 10% takes as long as the first 90%. I swear I was almost done months ago… but kept finding small bugs and edge cases, and things that weren’t behaving as I wanted.

I plan to flesh this writeup out later, but for now…

Demo

Links

GitHub

Etsy

I had this nice walnut board lying around, and also had committed to playing a little gig at a series my friends in Fort Collins run called Noise Floor. So why not make the most out of that hard deadline and try to make an instrument out of the board so I can play it at the show? Given how little I know about electric instruments, this came out surprisingly well, and sounds surprisingly good thanks to the stereo contact mics + pre-amp.

Here are the main features:

• Solid walnut body
• Moveable frets
• 2 embedded contact microphones
• DIY single coil pickup
• Hot-swappable pickup system
• Walnut + brass frets w/ 3D printed “legs” that go through the slots
• Spring on the bottom for sustain
• Custom stereo contact mic PCB

And a demo vid if you want to hear some audio samples.

Here are the main features:

• Solid walnut body
• Moveable frets
• 2 embedded contact microphones
• DIY single coil pickup
• Hot-swappable pickup system
• Walnut + brass frets w/ 3D printed “legs” that go through the slots
• Spring on the bottom for sustain
• Custom stereo contact mic PCB

I used 3D printed router jigs for the slots and other cutouts. For my first time trying this in earnest, and it worked pretty well.

In the making

Here is the raw board after surfacing and some sanding.

Here you can see the slots on the back, and how the frets are attached. The black knobs are 3D printed caps superglued onto M3 bolts. These feed up into a captured nut within the 3D printed fret attachment.

The pickup was created by 3D printing the bobbin, sticking some magnetic pins in it, and winding it with a hand drill jig. I ran out of wire so wasn’t able to spool it completely, hence the not great sound. Thankfully I made it modular, so it’s easy to pop out whenever I get inspired to make a new pickup. Harbor freight lever wire connectors do the Job. I used large ones in case I want to experiment with running multiple pickups in parallel, which I think is a thing you can do?

The pickups are mounted on a spring …. for the purposes of tremolo, was the idea. The problem here is that the contact mics pic up every little spring squeak, so it’s not too practical to move the pickup around while playing unless just using the pickup output.

And finally a closeup of one end so you can see the nice walnut grain pattern. I finished it with a hardwax oil – Rubio Monocoat. It has a nice satin finish which I enjoy.

In summary, it’s probably easier to make an electric stringed instrument than you think. If you don’t want to bother with the DIY pickup, just buy one from a used store or online for like 15 bucks. If you don’t want to do that, just grab a piezo disc or 2, solder them to an old aux cable that’s been snipped, and you’re done. So go give it a shot.

I’m of the opinion that faders are better than twist pots, and wanted something compact that I could use to control a bunch of parameters in an Ableton drum rack. I also wanted to solve the “jumping” problem that you have when using a controller with multiple banks – if you change a bank, you don’t know what the real position of the knob should be, and it’s easy to accidentally jump to a wildly different value than you want just by slightly moving the potentiometer. Here are the features that the LumaFader has, some of which help solve this problem.

Demo

Features

• 4 x long-throw faders for precise control
• 4 x mechanical keyswitches for bank management
• 16x RGB LEDs per fader to show the last fader position for that bank
• “Pickup” mode – only send a message when the last value is passed
• USB C for easy connection to your computer / phone / whatever
• Mini TRS Out to directly connect to a synth
• 17 banks = 68 total assignable sliders

Usage

I designed this to use with a drum kit in Ableton. For example, you can map the global sliders to overall kit FX (reverb, volume, filter, etc.). Then, map each bank to an individual sample’s parameters. So holding one button will access 4 parameters of the drum sample, holding another button will access 4 parameters of the snare sample, etc.

• Move slider(s) to send CC messages
• Hold button(s) to access other banks of CCs
• Double click a bank button to lock the bank (otherwise the global bank will be used if no buttons held)
• CC messages are only sent if the slider moves past the last value sent (as displayed on the LEDs next to each slider)
• You can also enable jump mode – send CC messages immediately if the slider is moved

Design

I had already successfully designed a custom PCB based off of the RP2040 – see the Loopster 2.0 – and each time I design a PCB, I try to do something I haven’t done before in order to improve. In this case the new elements were USB C – I’ve only ever used micro USB in the past – and the use of a large number of RGB LEDs (NeoPixels). I’ve used these pixels in the past, but this project uses 69 of them – a good factor of 4 more than the Loopster 2.0 has.

First, I had to add the RP2040 and the associated circuitry. Following the RP2040 hardware design guide  I added the appropriate power regulator, memory chip, crystal, and decoupling caps. The only changes I made from the official design:

1. Swapped the ceramic cap on the power supply with an electrolytic – something that a Redditor suggested. This seems to have eliminated the high pitched buzz you can sometimes hear.
2. Swapped micro USB for USB-C. This ended up being simpler than I expected – just needed a few extra resistors

power regultor and USB C changes

The rest of the circuitry is pretty straightforward – connect the slide pots to the analog pins of the RP2040, connect each button to a digital pin, and then connect the neopixels to one digital pin. These tiny addressable RGB LEDs are great in that they only require ONE digital pin for all of them. Finally, add the TRS MIDI Out circuit, which requires just one more digital pin.

TRS Midi Out Setup

Here is the full schematic

Full Schematic – Main

Full Schematic – LEDs and Pots

Layout

The goal was to make this device compact and portable, so efficient use of space was a priority. I used the middle of the board to house the main circuitry, the left for the buttons, and the right for the 4 large sliders. I decided to break out some additional GPIOs from the RP2040 since I didn’t use them all. I don’t have any plans for these, but perhaps in the future they can be used for something?

PCB Layout

3D Renders

Enclosure

I usually go with a 3D printed enclosure made from PETG, but this time wanted to try the ol’ “PCB Front Panel” trick. I drew up a simple front panel in KiCad and included holes for all of the LEDs, Sliders, and Buttons. I thought they came out great, especially considering how cheap they are to get made. I used some brass standoffs to connect the main board and the front panel.

Assembled device with front panel and diffusers

The tiny LEDs shining through the panel holes were a bit harsh, so I designed little diffuser inserts and printed them out of transparent PETG, which did the trick. Note that the bottom layers are printed in black PETG in an effort to prevent too much bleeding between the pixels.

3D printed LED Diffusers

For the hell of it, I also created a nice Walnut case for one of them. I designed a router template in Fusion 360 and hand routed it out of a solid block of walnut. It was then hand sanded to a high grit and finished with a hardwax oil (Rubio Monocoat)

Walnut Enclosure

Software

I’ve ripped a lot of tapes over the past few years and finally landed on an efficient method of ripping, tracking, and labeling the tapes. It’s super simple but perhaps it will help. The TLDR version is:

• Turn on auto record / auto stop on your field recorder.
• Plug an RCA -> aux cable into the field rec device and press record.
• Put a post-it on the cassette shell / record sleeve. Take note of the side, and the filename on the field recorder.
• Keep doing this until the SD card is full.
• Empty the SD and rename according to your post-its.

Steps

1. Grab your media, post-it notes, field recorder,and aux to RCA cable
2. Go into your field recorder settings and turn on auto rec on and off. Experiment with the dB threshold settings. I set the stop threshold to something really close to the minimum, and the auto start recording threshold set to a bit more than that.
3. At this point you might consider powering your field recorder via a large usb power bank or a brick, if that’s an option. Mine is plugged into a brick and it’s very nice to never think about batteries.
4. Now you can just press play and let it start recording.
5. Slap a post-it note on the cover / case and note a reference to the file name of the recording file, and which tape/side it corresponds with.

filename on zoom h2n

post it note with notes about filenames

1. Repeat until your SD Card is full. With auto record you don’t even need to press record. Just pop out the old and pop in the new and press play.
2. Transfer the files to your computer.
3. Grab your stack of sticky noted media and reference the filenames with the post its to figure out how to name the file. Here’s what mine usually look like.

final filenames in Finder

1. Reformat the SD card
2. Start over and do this forever and ever until you run out of tapes or die
3. Go to the thrift store and get MORE tapes to feed your addiction
4. Check into rehab
5. Relapse. Spend your life’s savings on eBay cassettes.

R.I.P