This is my Arduino sketch for a Software Defined Radio, using an Elektor SDR Shield 2.0 connected to an Arduino Uno. The SDR shield was released in Elektor Magazine 7/2018 with some basic firmware. It can be controlled by a PC via the Arduino's USB interface, but only few SDR programs support the original command set, e.g. G8JCFSDR. Meanwhile the firmware had some improvements, but it is still very basic and has its limitations. Therefore, I wrote my own software for fun and added a few useful functions:

• A subset of the well documented Yaesu FT-991 CAT serial protocol is used instead of the proprietary serial protocol from Elektor. This allows you to control the SDR hardware by more SDR programs on Windows PCs, on Linux PCs or on Macs.
• A standard 2 lines by 16 characters LCD with an I²C interface is used for displaying useful information about the status of the SDR. The display is connected to the Arduino's I²C pins SCL and SDA and its I²C address is 0x27.
• A rotary encoder can be used to change the RX frequency as in commercial amateur radio transceivers.
• TODO: A 4 x 4 keypad can be used to enter the RX frequency directly. The keypad needs only one analog input pin on the Arduino.

The ArduSDR supports the following subset of the most commonly used Yaesu FT-991 CAT protocol commands. See [2] for a more detailed description.

• Etherkit Si5351 version 2.1.4 by Jason Milldrum
• LiquidCrystal I2C version 1.1.2 by Marco Schwartz
• Encoder version 1.4.2 by Paul Stoffregen
• TODO: OnewireKeypad version 0.0.0 by Andrew Mascolo

• Integrated WSPR encoding and modulation
• Morse code encoder and decoder
• RTTY encoder and decoder

[1] Elektor SDR shield: https://www.elektormagazine.com/magazine/elektor-201807/41737

[2] Yaesu FT-991 CAT Operation Reference Manual: https://www.yaesu.com/downloadFile.cfm?FileID=10604&FileCatID=158&FileName=FT%2D991%5FCAT%5FOM%5FENG%5F1612%2DD0.pdf&FileContentType=application%2Fpdf