ADAU DSP audio CW filter

Some time ago friend of mine OK1DXD searched for audio CW filter for his oldtimer radio. We found a nice DSP board on Aliexpress - New ADAU1401/ADAU1701 DSPmini Learning Board Update To ADAU1401 Single Chip Audio System, so we decided to test it... I don't want to present you a complete manual how to build a AF CW filter, but rather to show you interesting new technology.

The ADAU module

The heart is Analog Devices DSP machine ADAU1401. There are many useful blocks inside, like SD ADC and DAC converters in audio quality, general IO ports, controller,... The only other thing on board is an EEPROM, holding the program. There are 2 ways how to put the program into ADAU: directly by programmer interface (in my case by I2C, usefull in debugging phase) or in selfboot mode from EEPROM. So when the EEPROM is programmed in advance, the board can operate complete independently.

Analog Devices offers free tool SigmaStudio that can be used for application development, ADAU hardware register configuration, upload application to module, in limited way to debug it in device and, when needed, to program the EEPROM on board. All communication with module run over single I2C interface.

You need an converter between USB PC port and I2C. Analog devices offer for that a programmer called "USBi". It is hard to get and quite expensive. Fortunatelly there is other way - a programmer using Cypress (now Infineon) chip, available at reasonable price - EZ-USB FX2LP CY7C68013A USB Core Board Development Board USB Logic Analyzer With I2C Serial SPI Interface Module Mini USB. It needs an appropriate driver and does the same es the USBi. See

A very nice article describing how to put all that things in work is at
I don't want to introduce you into ADAU programming (but it is surprisingly easy, no need to write lines of code, all is done mostly by connecting graphic blocks) - there is enough online help pro Analog Devices. You can see how the IDE looks on this picture (click to erlarge), together with calculated filter characteristics.

Here you can see my prototype.

I put together the ADAU board and the programmer, to make the experiments easier. Just few words about protype functionality. Control is done by rotary encoder (rotate: bandwidth selector - 200 Hz, 400 Hz, path thru, push: toggle audio input1 and 2). Accepts up to about 5V AF input signal, output is approx the same level - more than enough for headphones. In download section you can find all the project files. Here just for quick overwiew the circuit diagram...


KiCAD project files - circuit diagram, PCB
SigmaStudio files - the program
Captured web page dauemo.
Current version of free USBi driver.
Datasheets of related parts.

73 OK1DX