CTR2 is a unique human-machine interface (HMI) that allows you to control and manage up to 16 radios and 8 antennas using a small touch screen user interface on your desktop. 

The CTR2 system is based on the Teensy 4.1 development board and audio interface provided by PJRC.com. The Teensy 4.1 features an ARM Cortex-M7 processor running at 600 MHz. Audio DSP processing is handled by a NXP SGTL5000 codec on the PJRC Rev D Audio Adapter board. The firmware is based on the Teensyduino 1.54 library, and uses the Arduino ecosystem. This library allows the Teensy 4.1 to be programmed in Arduino C/C++ and provides an extensive set of tools. It also provides a wide selection of easy to use audio tools that operate in the digital domain such as amplifiers, mixers, tone generators, tone detectors, equalizers, compression amps, and FFT frequency analysis. These functions are available for any radio connected to the system, from the latest all digital SDR radio to the oldest boat anchor.

A Nextion 3.5″ or 5″ Enhanced HMI touch screen display and one rotary encoder handles the user interface. Provisions have been made to allow mounting the display and encoder in the same enclosure as the HMI or they can be remotely mounted in a small wedge shaped enclosure. Remote mounting lets you place the display anywhere it’s convenient. Tuning and parameter changes are managed using the touch screen, encoder, a USB keyboard, or a USB mouse.

The functional drawing in the lead photo shows a system with four radios and four antennas. Additional Radio I/O modules and antennas can easily be added to expand the system to control 16 radios.

The first CTR2 article covering the basic system was published by the ARRL in the September/October 2021 issue of QEX magazine. A follow-up article describing the radio I/O and antenna switching options supported by the system is scheduled to be published in the November/December issue of QEX. For now, this blog will focus on the HMI, Display, Auxiliary, and Radio I/O portion of the system. Once the article on the switching options has been published, I’ll add additional information on them to this blog.

This is a experimental project and the schematics and source code are available (search the Download category). The source code for this project is copyright 2021 by Lynn H. Hansen. All code is open source and is subject to the terms of GPL3 (GNU GENERAL PUBLIC LICENSE, Version 3.0, 29 June 2007).

The design required extensive use of SMT devices to keep each board’s size to 4″x4″. I can supply complete and tested HMI, Display, and Auxiliary boards. The builder will need to supply the Nextion display, Teensy 4.1, Teensy 4 Rev D Audio Adapter, ESP8266-01, a rotary encoder, an SD memory board, and an external power switch. The external Radio I/O and switch boards are supplied with only the SMT components mounted. The builder must supply the through-hole components and connectors to finish them. Interactive bill-of-materials (BOM) files and an Excel BOM spreadsheet are also available in the Download section.

Please note:
This is NOT a beginners project. It will require good soldering skills and the ability to fabricate ribbon cables for the board interconnections. In addition, experience with the Arduino IDE (or other supported IDE such as Microsoft Code or Visual Studio) is required as you will be downloading code to the Teensy 4.1 and the Nextion display.


I’m thinking about releasing videos on YouTube. Let me know in the comments if this would be of interest to you.

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