Introduction

PCB Docs STLs Firmware

This is a simple drum machine / loopstation. It's made for three hand-wound solenoids mounted to a tambourine. It is controlled by a Raspberry Pi Pico on a custom PCB.

See this blog post for some more context.

assembled prototype

Prototype

This is the hardware design for the initial prototype gifted as a birthday present. It's a single sided PCB layout suitable for hand etching at home.

hand etching prototype pcb assembled prototype

You can also download the Gerber files to order PCBs online.

Bill of Materials

These are all the parts required to assemble the prototype.

IDTypeLink
U9Raspberry Pi PicoReichelt.de, Amazon.de
U2TP4056 Charger ModuleAmazon.de
U4, U6, U8MOSFET Module N-ChannelAmazon.de
U3, U5, U7Step-Up Converter ModuleAmazon.de
J2SSD1306 128x64 0.96" DisplayAmazon.de
S1ALPS EC12E24244Reichelt.de
-Cap for encoder knobReichelt.de
D1 - D4LED 5mmReichelt.de
D5 - D81N5819 Schottky DiodeReichelt.de
R1 - R4Resistor 1k OhmReichelt.de
R5Resistor 10k Ohm 0.1% AxialReichelt.de
R6Resistor 18k Ohm 0.1% AxialReichelt.de
SW1 - SW412mm waterproof stainless steel push buttonN/A
SW5AUnknown Power SwitchN/A

Prototype Schematics

This page shows the current version of the schematics as SVG graphics.

You can also view the schematics as PDF.

drumkit

Direct link to drumkit.

Prototype PCB Layout

This page shows the current version of the PCB layout as SVG graphics.

You can download the Gerber files to order PCBs online.

2D PCB Layout

You can also view the 2D PCB layout as PDF.

Direct link to this file.

DIY Version

The DIY version is suitable for etching at home, it only needs the bottom copper layer. Be aware that there is one track on the top layer, for a safety diode that was added later. This connection should be done with a wire by hand.

You can also view the DIY layout as PDF.

Direct link to this file.

3D PCB Layout

Status: "Preparing 3D model..."

LARS V2

This is the second iteration of the hardware. The principle is the same as for the prototype, with the same chinese modules used. Only the buttons have been changed, and there are now 9 of them, with 8 LEDs. The battery is now mounted on the board. It is planned to be used without a case.

You can download the Gerber files to order PCBs online.

assembled V2 PCB

Revision 1 was using the SMD-only footprint for the Raspberry Pi Pico. Revision 2 has changed this to be compatible to THT as well.

Warning: Revision 1 and 2 are missing diodes on the button matrix. So when holding down three or more buttons simultaneously you get ghosting on other buttons.

Bill of Materials

These are all the parts required to assemble the V2 PCB.

IDTypeLink
U1Raspberry Pi PicoReichelt.de, Amazon.de
U2TP4056 Charger ModuleAmazon.de
U3 - U5MOSFET Module N-ChannelAmazon.de
U6 - U8Step-Up Converter ModuleAmazon.de
OLED1SSD1306 128x64 0.96" DisplayAmazon.de
BT1Keystone 1042Reichelt.de
S1APEM 5236ABReichelt.de
SW1ALPS EC12E24244Reichelt.de
-Cap for encoder knobReichelt.de
SW2 - SW10DIP 6x6mm push buttonReichelt.de
D1 - D41N5819 Schottky DiodeReichelt.de
D5 - D12LED 5mmReichelt.de
R1Resistor 10k Ohm 0.1% AxialReichelt.de
R2Resistor 18k Ohm 0.1% AxialReichelt.de
R3 - R10Resistor 1k OhmReichelt.de

LARS V2 Schematics

This page shows the current version of the schematics as SVG graphics.

You can also view the schematics as PDF.

lars2

Direct link to lars2.

LARS V2 PCB Layout

This page shows the current version of the PCB layout as SVG graphics.

You can download the Gerber files to order PCBs online.

2D PCB Layout

You can also view the 2D PCB layout as PDF.

Direct link to this file.

3D PCB Layout

Status: "Preparing 3D model..."

3D Print - Solenoids

This page shows the 3D printed parts for the solenoid actuators.

The dimensions for the parametric OpenSCAD settings for these generated STL files should match what we used for the prototype. For your own build you may need to get the OpenSCAD sources from the repo and tweak the values.

Actuator All

Status: "Preparing 3D model..."

Direct link to this file.

Actuator Cap

Status: "Preparing 3D model..."

Direct link to this file.

Actuator Hammer

Status: "Preparing 3D model..."

Direct link to this file.

Actuator Spool

Status: "Preparing 3D model..."

Direct link to this file.

3D Print - Tambourine

This page shows the 3D printed parts to mount solenoids to a tambourine.

The dimensions for the parametric OpenSCAD settings for these generated STL files should match what we used for the prototype. For your own build you may need to get the OpenSCAD sources from the repo and tweak the values.

Beam

Status: "Preparing 3D model..."

Direct link to this file.

Tamb Mount All Visualize

Status: "Preparing 3D model..."

Direct link to this file.

Tamb Mount Inner

Status: "Preparing 3D model..."

Direct link to this file.

Tamb Mount Outer

Status: "Preparing 3D model..."

Direct link to this file.

3D Print - Prototype

This page shows the 3D printed parts for the prototype PCB.

The dimensions for the parametric OpenSCAD settings for these generated STL files should match what we used for the prototype. For your own build you may need to get the OpenSCAD sources from the repo and tweak the values.

Enclosure Bottom

Status: "Preparing 3D model..."

Direct link to this file.

Enclosure Top

Status: "Preparing 3D model..."

Direct link to this file.

Enclosure Faceplate

Status: "Preparing 3D model..."

Direct link to this file.

Usage Guide

Turn on LARS using the power switch on the PCB.

In normal operation, the bottom of the display always shows the battery level in percent, and the voltage. Take care to turn off the device and recharge it when the percentage reaches zero!

The top of the screen shows the currently selected setting and its value. Press the encoder to switch to the next available setting, or turn the encoder to change the value of the currently selected setting.

The available settings depend on the current mode. Take a look at the sub-page for each mode for details.

You can hold down some buttons while powering on the device to get different effects:

  • hold the Clear button to enter the configuration menu
  • hold the encoder Click button to show version information of the firmware
  • hold both Clear and Click to enter the button test mode
  • hold any combination of three buttons to skip the boot animation

Loop Station

LARS Loop Station controls

In this mode the first three buttons play each corresponding output channel.

The fourth (and eighth) button, with the LED always lit, is the record button. Hold it down for a while and release it to set the length of the loop.

Notes played while the record button is held will be looped.

The fifth, sixth and seventh buttons are channel mute buttons. While holding these down the corresponding channel will not play any notes.

The top-right button below the encoder clears the recorded loop in different ways:

  • Pressing it on its own will clear all channels of the current loop, keeping the set length.
  • Pressing it while holding down one of the channel mute buttons will clear only this channel in the current loop.
  • Pressing it while holding down the left REC button will clear the current loop, including the length.
  • Pressing it while holding down the right REC button will clear all loops in all banks.

You can modify the loop length using the encoder menu.

The encoder menu also provides a way to switch between different loop banks. With the Sel-Bnk menu you can switch to another loop bank. With the Cpy-Bnk menu you can copy the current loop to another bank and switch to it.

Drum Machine

TODO: work in progress

MIDI

The MIDI mode is only available when a computer is connected via USB to the Raspberry Pi Pico.

You only have two settings in this mode, the receive and transmit MIDI channels, ranging from 1 to 16.

Notes received on the selected Rx channel will be played on the output channels. Velocity is ignored.

Any pressed note buttons are sent on the selected Tx channel.