Lock-in+PID is an application for the RedPitaya enviroment / STEMlab 125-14 board that implements an Oscilloscope application and a Lock-in amplifier. It’s based on relese-0.95 scope application of the RedPitaya project.

The aim of this application is to provide a toolkit for labs measurements and system control uses. The functionalities are organized in “instruments”.


A rigorous description of the App design and applications can be find in this article on scientific journal: Compact embedded device for lock-in measurements and experiment active control.

Pre-print Arxiv (open) Review of Scientific Instruments


Where to start

If you want to know more about how to use this app you should read the TheApp > Instruments menu.

Download and install

For the last release, check TheApp/install/. The application comes in three flavors: Default, DEBUG and RELOAD. You’ll be looking probably for the Default option.


The source code is available at GitHub

Source Code

The project code is available on GitHub: github.com/marceluda/rp_lock-in_pid/

The App Web GUI

app gui

Use cases

The application implements a lock-in amplifier and two PID filters. These elements are suitable for several stabilization schemes implementations: they measure low amplitude signals to get a physical system state and then use a closed-loop feedback system to stabilize the state of the physical system to a desired one.

The closed-loop system is an stabilization-scheme, usually descrived in control theory. The actually probed schemes are mostly from laser-optics applications, because Lock-in+PID was created in an optics lab with this purpose. But all off then are ready to use in any physical system o engineering project controlled by electric signals.

Lock-in+PID most common usage

Phase sensitive measurement of small signals

Closed loop system schemes for variable stabilization

Combined systems

Applications tested in lab

  • Stabilization of laser wavelength to atomic transition
  • Stabilization of laser wavelength to Fabry-Perot interferometer (Pound-Drever-Hall)
  • Stabilization of VCO frequency to an electronic reference (Crystal or RCL circuit)

Derivated works

Same versions of the same App witho minor changes where made for specific features and applications. The known works are listed in: TheApp > Derivated works menu.