Deepstomp: Low-Cost High-Performance DIY Multi-Effects Pedal/Stompbox Platform

Figure 1. The Low Price of DSP Microcontroller Advertised in An Online Store (Upper) and DeepStomp Digital Pedal Mock-Up (lower)


The advance of today’s digital electronics bring a new hopes for many things, because now there are many choices for low cost and high performance DSP microcontrollers. For example, a small board, popularly called “blue-pill”, is advertised in an online store for only US$ 2.25 (Figure 1.-upper part). It has 72MHz 32-bit processor core with some DSP instruction sets (ARM Cortex M3), 20kB RAM, multi channel 12-Bit ADC (can be expanded to 15-bit by multichannel oversampling), 4 PWM output, various communication peripherals, and many digitalĀ  IO pins. This ridiculously cheap development board is very tempting not only for just develop new product but also for embedding it into the final product as its core component.

Deepstomp: A Low-Cost High-Performance DIY Digital Effect Pedal (Stompbox) Platform

To take benefit of this digital technology for everyone, I had decided to design an open platform (open source hardware and software) for DIY digital stompbox/effect pedal which is based on “blue-pill” as its core, and I name it as Deepstomp. Now the development is in progress and you can see the mock-up in the Figure 1 (lower). It’s not officially released yet, but here can share some leaks, the schematic diagram of the pedal and some of its design aspects, see it in the Figure 2.

Figure 2. Deepstomp Main Board Circuit Schematic Diagram

We can discuss some main features of the circuit design here: the analog/digital input-output conversion, theĀ  user interface for parameter control and visualization, and the serial communication port for programming and pedal control extension.

  • Input/output analog-to-digital and digital-to-analog conversion is done using the built-in ADC and PWM generator. Using multichannel expansion oversampling, its 8 channel reading of 12-bit ADC should theoretically result in 15-bit final resolution for the input conversion. The output conversion is done using cascaded 8-bit PWM with automatic calibration to produce 16-bit resolution with no missing-steps nor over-steps error.
  • User interface (to be continued)