A small CW decoder

 Another Cassette Box project ...

I wanted a small portable CW decoder, and since I'm a big fan of using old cassette tape boxes, it had to fit in one of those.

The decoder is based on the work of Budd, WB7FHC, which is also used in the OST Morse Box project. You can find the original here: https://wb7fhc.com/m2-cw-decoder.html 

His project uses a 20x4 LCD display which is too big for my project, and the OST Morse Box was rewritten for a small OLED display. So what I did is just program an Arduino Nano with the complete OST Morse Box firmware (largely overkill, I know), but only connecting an OLED display, and an LM576 tone decoder circuit.

The firmware can be found here: https://github.com/on7dq/OST-Morse-Box-V3
The easiest way is to use the HEX file with Xloader (first file in the list), no need to open the project in the Arduino IDE.

The decoder circuit was described in the user manual for V2, and can be found here: https://github.com/on7dq/OST-Morse-Box-DG

The output of the decoder (LM567, pin8) goes to pin D2 on the Arduino. It's also best to connect pins A6 and A7 to ground, since I don't use any potmeters. Some of the parameters can still be set via the Windows Control program. 

OLED connections are straightforward : GND and Vcc , SDA to A4 and SCL to A5.

The Arduino + OLED + decoder fitted nicely on a piece of perfboard, and I even could put a 1200 mAh Li-Po battery in the case. See picture at the top for the front view. 

And this the back. The battery has a 4 pin header (bottom right), but only pins 1 and 3 are used. It connects to a small charger board. When the pins are inserted the wrong way, nothing happens (I hope 😉).

Charger board connected: