All postsMindy: a paper screen for your pedalboard
A control surface with an e-paper screen that hosts a Bluetooth macro pad, sends MIDI to your pedals, and advertises itself to Taurus — all at once. With a demo against an Ampero II Stage.
Mindy: a paper screen for your pedalboard
Mindy is a control surface. It is a small module with an e-paper screen that
sits on your board, talks Bluetooth MIDI, and drives Taurus and your hardware
pedals from the same set of buttons.
Here it is running against an Ampero II Stage — Mindy is the little screen in
the middle of the board, and the presses on it are moving the Ampero.
The problem it solves
A footswitch with an LED can tell you one bit of information: on, or off. That
is fine when the switch does one thing forever. It stops being fine the moment
the same switch means "scene 2" on one rig and "toggle the fuzz" on another,
which is exactly what happens when you play more than one kind of gig.
Put a screen above the switches and the surface can say what it is about to do,
in words, and change its mind between songs.
What it actually is
Mindy runs on an M5Stack PaperS3 — an ESP32-S3 module with an e-paper display.
It does three things at once, which is the interesting part:
- Hosts a BLE HID controller. Pair a cheap macro pad to it and those keys
become footswitch inputs. We use an XPPen ACK05, because it is a well-built
little control surface with real buttons and a dial, and it costs a fraction
of a purpose-built MIDI pedal.
- Sends MIDI out to a pedal. It scans for and connects to BLE-MIDI hardware
— WIDI adapters, PuckCC, or a pedal with Bluetooth MIDI built in — as the
central.
- Advertises itself as a BLE-MIDI device. So Taurus on a Mac or iPad can
connect to it directly through Apple's Bluetooth MIDI browser, with no dongle
in the chain at all.
The Links screen has two independent selectors, one for the controller coming
in and one for the pedal going out. Only one Bluetooth scan can run at a time,
so starting one cleanly stops the other — a small thing that took some care,
because BLE stacks are unforgiving about overlapping scans.
Two targets, one profile system
Choose Taurus · Mac / iPad and Mindy loads the first-party Taurus profile
and keeps its own BLE-MIDI peripheral available for the Mac to find. Choose
Ampero II Stage and it loads the Ampero mapping and goes hunting for a
BLE-MIDI peripheral to connect to as the central.
The profile is persisted, so it survives a reboot — which matters, because the
first thing a control surface must do is come back up in the state you left it.
The Taurus contract is deliberately simple and channel-agnostic:
Trigger buttons send a non-zero press followed by a zero release, so repeated
taps are independently edge-detectable rather than merging into one long hold.
The screen is the point, and the screen is monochrome
E-paper is a strange choice for a live device until you have stood on a stage
under a white LED wash and tried to read a backlit screen. E-paper has no
backlight to blow out, holds its image with no power, and is readable at any
angle. What it is not is colourful, or fast.
Mindy is a Gea app, which means the same source runs in a browser simulator and
on the hardware. The interesting trick is how it handles being two very
different displays: a @media (monochrome) stylesheet forces the hardware
presentation to pure black and white, while the browser keeps a richer dark
theme. One app, two presentations, no forked layout code.
The PaperS3 target runs at DPR 2, giving a 270×480 logical scale on the 540×960
panel — so type and controls are sized in hardware-honest units rather than
being scaled down from a desktop mock and becoming illegible.
Why build the surface ourselves
We did not set out to make hardware. We set out to make Taurus controllable by
foot, discovered that the affordable end of the MIDI-controller market is either
unlabelled switches or a desktop editor from another decade, and concluded that
the surface was part of the product whether we liked it or not.
The bonus is that once you are building a small computer that lives on a
pedalboard, sends MIDI, and has a screen, you are one uncomfortable question away
from asking what else a small computer on a pedalboard could be doing.
We asked. The answer involved putting a NAM profile on a microcontroller,
and it worked better than it had any right to.