This product was designed by David Haillant.
By buying this product you support original hardware creators.
The simplest Triangle/Square wave Oscillator for your Eurorack Synth
Simple LFO — Triangle & Square Wave Oscillator
A rock-solid, no-frills LFO module for Eurorack systems. Built around a classic integrator + Schmitt Trigger circuit, it generates clean triangle and square waveforms across an enormous frequency range — from ultra-slow modulation to audio-rate oscillation for drone synthesis.
Features
- Two waveform outputs — triangle and square, simultaneously available
- Two frequency ranges — LO and HI, selected via a SPDT switch
- Amplitude control — onboard potentiometer to scale the output level
- Bi-color LED — visual feedback of the oscillation cycle
- Eurorack standard power — ±12V, less than 20 mA total draw
- Compact footprint — 4HP, PCB 5×5 cm
Frequency Ranges
| Range | Min | Max |
|---|---|---|
| LO | 2.5 mHz (0.0025 Hz) | 2.4 Hz |
| HI | 250 mHz (0.25 Hz) | 245 Hz |
Output Specifications
Powered at ±12V:
- Triangle: ±6.3V peak-to-peak
- Square: ±5V peak-to-peak Output amplitude adjustable via the Amplitude potentiometer.
Use Cases
Plug it into any CV-capable module — VCO, VCA, VCF, or anything else that accepts a control voltage. At higher frequencies, use it as an audio source for raw, lo-fi drone textures. Pair it with an Attenuverter/Inverter module if you need to scale or invert the signal.
Build Info
An easy build, suitable for beginners. Expected assembly time: under one hour. Tools required: soldering iron, solder, and cutting pliers.
Kit includes: resistors, capacitors, 9mm potentiometers with Davies 1900h knobs, connectors, two SPDT switches, IC + socket.
Front panel: 4HP, 1.6mm black PCB material, sold separately or available as an option.
Note: PCB silkscreen and solder mask may show minor cosmetic variations — this is normal for PCB manufacturing.
Version History
| Version | Change |
|---|---|
| 1.1 | TL072 replaced by TL074 |
| 1.2 | Added Amplitude potentiometer — new panel layout |
| 1.3 | Bi-color LED added — same panel as v1.2 |
| 1.4 | LED circuitry inversion corrected |
| 1.5 | R4 removed, square wave amplitude normalized to ±5V |
Current version: 1.5
Documentation
- Build guide & BOM (PDF)
- Interactive BOM
- Full documentation & updates As featured in Kristian Blåsol's Modular In A Week — Episode 4.1
Links to code and documentation
Documentation (davidhaillant.com)
Schematics (davidhaillant.com)
Shipping policy
Orders are usually shipped within the week following purchase.
Smaller items (PCBs, assembled PCBs, and small kits) are sent in letter format (padded envelope), while larger items are sent as parcels.
Shipments within France and the EU are only tracked when sent as parcels.
Shipping to the rest of the world is available. Please contact me if you have any questions or concerns.
The seller
Designed with care and attention to detail. I have a deep love for old-school synths and the DIY spirit, so every module is made to be approachable for beginners while packing real character for seasoned builders.