FV-1 Sandbox is a self-contained open-source development platform for the Spin FV-1 digital signal processing (DSP) integrated circuit.
The Spin Semiconductor FV-1 IC was developed by Alesis alumni Keith Barr and Frank Thomson. It features an integrated architecture with built-in analog-to-digital and digital-to-analog converters, memory, and processing core. It requires only a few external components to operate, and can run user programs from an inexpensive serial EEPROM. It has been used in hundreds of different pedals and devices, with many hundreds of thousands of units in service.
The FV-1 has seven built-in programs that cover a wide range of effects, but most designers leverage the custom code capabilities of the chip. The Fv-1 is programmed in SpinASM, a proprietary assembly language. Spin provided a free integrated development environment for Windows computers called SpinASM IDE. This interfaces with a development board fitted with a Cypress PSoC microcontroller functioning as a USB interface. The IDE allows for code editing, rapid auditioning of DSP algorithms on the development board, and production programming using multi-algorithm .SPJ Spin Project files. No MacOS or Linux programming tools were made available, and SpinASM also had issues running on newer versions of Windows. A patch was released to fix compatibility issues under Windows 7, and this version (1.1.31) works with most Windows 10 and Windows 11 systems. The IDE does also run under Windows for ARM, but support for the PSoC-based development board is broken due to driver issues.
Our intention is to create a complete toolchain that can run on any modern computer that interfaces with a high-quality hardware platform for deploying algorithms. To this end, we have created an open-source assembler that runs in a web browser and a hardware platform that interfaces with an inexpensive RP2040 microcontroller for programming. The hardware platform may be assembled without the microcontroller for higher-quantity production use, and the RP2040 programmer may be used in conjunction with either a TagConnect programming cable or pin sockets on the PCB for production programming.
We've been using asfv1, an open-source assembler for FV-1 designed by Nathan Fraser. It works great but requires a few steps to deploy as part of a larger toolchain. It works with Sublime Text or Notepad++ to create a DIY development environment, but it's still a lot of work for a new user. So we decided to build a one-stop shop!
We patched up some bugs we found, added some quality-of-life improvements, and ported the whole thing from Python to JavaScript so we could run it in a browser. There's a pretty decent code editor using Monaco, an assembler, and a one-button deployment to the Sandbox hardware.
The hardware is very simple, incorporating a high-quality analog front-end that reduces out-of-band and clock noise from the FV-1. It's full stereo, features three user potentiometer controls, and two toggle switches for selecting one of six possible algorithms. It also uses program zero to bypass the effect, allowing stereo switching without any external hardware or relays, albeit at the cost of higher noise floor and a slight delay from the DSP ADC+DAC conversions.
Programming is accomplished using the aforementioned RP2040 board - we've used a Waveshare RP2040 Zero for its compact form factor and handy USB-C port, but clones of this part or other variations may also work. the RP2040 code is implemented in CircuitPython for ease of deployment and modification. To program a new algorithm on the Sandbox EEPROM, simply copy an assembled .HEX or .BIN file to the RP2040 CIRCUITPY or SANDBOX removable drive. Name the program 0.HEX to program algorithm zero, 1.HEX for program 1, and so on. Adding any other named .BIN or .HEX file will write program #3, which is the program accessed if no toggle switches are assembled to the Sandbox PCBA.
We've also added an FV-1 simulator to the web app. The assembled program runs through a software model of the chip at its native 32.768 kHz, so you can audition an algorithm on a test tone, an audio file, or live input before you ever program the hardware. The three pot controls are on screen, and each successful build reloads into the simulator while it plays. Two indicator lamps follow REG30 and REG31. The simulator models accumulator saturation and the FV-1's companded delay memory, and its LFO rates and depths follow the equations in Spin's application note AN-0001. Chorus interpolation is approximated, so always confirm a design on real hardware.
The simulator can also be played from a MIDI controller plugged into your computer. Press Enable MIDI in the simulator panel, allow the browser's MIDI prompt, and pick an input and channel. CC50, CC51 and CC52 sweep POT0, POT1 and POT2, and CC102 switches the effect, with 0-63 bypassed and 64-127 engaged. MIDI moves the same controls the sliders do, at the full 128 steps a control change carries, so a program cannot tell the difference between a fader and a mouse. Note that the Sandbox pedal itself has no MIDI input - this drives the simulator only.
So it's a web app and a pedal. Hook 'em up and write some code!
The web app needs to be served over http - opening Assembler/index.html directly as a file:// page will not work. Browsers block the audio engine the simulator depends on from file:// origins, and the directory and serial access used to talk to the hardware need a secure context too. localhost counts as secure, so any static file server will do:
python3 -m http.server 8000 --directory Assembler
Then open http://localhost:8000 in Chrome or Edge. If you prefer Node, npx serve Assembler works the same way.
Chrome or Edge are required for programming hardware and selecting folders, since Firefox and Safari do not implement the File System Access and Web Serial APIs. The simulator itself works in any browser with AudioWorklet support, and its MIDI control works in Chrome, Edge and Firefox - Safari has no Web MIDI.
- ASFV1 Source: copies of the Python source for asfv1, the reference assembler this one is checked against
- Assembler: JavaScript Web Application for assembling FV-1 programs, including an in-browser FV-1 simulator (
fv1-emu.js/fv1-sim.js) with MIDI control (fv1-midi.js) - Firmware CircuitPython code for the RP2040 Zero program module
- spin-test Puppeteer scripts and sample FV-1 programs for testing the assembler:
npm run test:roundtripfor the assembler and simulator as a pair,npm run test:emufor the DSP core,npm run test:midifor the simulator's MIDI control, andnpm run test:pagefor the editor's unsaved-changes guard - Hardware Schematic and PCB files for Sandbox pedal hardware
We've released this project and all associated tools under the MIT License. This means that you can use the tools and information in this repository for anything you want, as long as you inform your users / customers / clients that you got it from us. You can modify or change anything here to suit your purposes, and you can make products that you sell for profit. You can even close your sources, so that what's in your product or project is private. You just have to credit us as shown in our license file. An example of what that looks like can be found in our Third Party Notices file.
Any projects you create with these tools belong to you. If you write your own code to process audio with this project, that code is under your copyright and is yours to do with what you wish. If you use someone else's DSP algorithms, that use will be subject to their license terms, and we're not able to help you sort that out. TL:DR you can do whatever you want with this repo, just give us credit.