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Red Pitaya Custom DAS

Oscilloscope Screenshot

Summary

This project realizes a system for measuring analog signals in the kilohertz to low megahertz range with a digital signal processing system in real time, offering an affordable alternative to expensive oscilloscopes and spectrum analyzers. The basic components of the system are a Red Pitaya STEMlab for signal acquisition and processing and a personal computer or mobile device for data visualization and further analysis.

To allow transmission over an Ethernet connection and to improve signal quality, the high-rate data stream coming from the STEMlab's analog-to-digital converter is decimated to a lower-rate signal using the integrated FPGA. During decimation, the signal passes through one of six filter chains to attenuate aliasing effects.

The chains run on the STEMlab's FPGA. They are based on a combination of FIR and CIC filters, and decimate the incoming 125MHz signal to output frequencies between 50kHz and 25MHz, depending on the chain. They achieve an aliasing attenuation of 60dB and exhibit negligible passband droop. A signal-to-noise ratio of up to 84dB has been measured.

The decimated signal is then passed on to an embedded GNU/Linux and sent to a client over a network connection. A newly developed oscilloscope application allows observation of the signal from a client device. The application is based on JavaScript, allowing for easy deployment across any platform with a modern browser available.

All components created for this project are provided under the MIT license. A comprehensive toolchain covering filter design, FPGA tools, embedded GNU/Linux and front end development, along with documentation, allows anyone to extend and modify the system and to tailor it to their needs.

Project Structure (Major Components Only)

.
├── design
│   └── filter: Filter design toolchain (Matlab)
│
├── doc
│   ├── report:         Project Report, Developer Guide, User Guide
│   ├── verification:   Measurement toolchain and results
│   └── vivado-install: Vivado install guide
│
├── env: Toolchain setup. Consult the Developer Guide for details.
│
├── firmware: The things which have to run on the STEMlab
│   ├── arm:  GNU/Linux and server for data transmission
│   ├── bin:  binary blobs for flashing
│   └── fpga: FPGA components: Vivado Projects and IP Cores
│
├── pm: Project Management Stuff
│   └── journal: Project Journal (misc. notes)
│
├── resources: Datasheets, manuals, various other resources.
│
└── scope: Oscilloscope Application