Firmware
MFJ-419 CW-Elmer firmware (no public download)
Not hosted — available from the manufacturer
The MFJ-419 is an ATmega328P + FTDI FT232RL design that emulates an Arduino Nano and is updated as an Arduino sketch (e.g. "CWE501.ino"); MFJ's manual says to "Download the firmware update from MFJ", but no firmware file was ever posted on the MFJ website or found anywhere else.
Read before installing. Manual V1A (2024): latest firmware 5.02 (loudness control, iambic paddle); board R1 is not compatible with 4.xx firmware. Procedure: Arduino IDE >1.8.16, Board Arduino Nano, Processor ATmega328P, the unit's COM port, open the .ino, Sketch > Upload; minor updates keep EEPROM settings, major ones may reset them. Firmware derives from David Duncan K7DUN's CW-ELMER, whose source he offered privately on request (no licence published). MFJ ceased on-site production on 2024-05-17 but kept selling stock and offering repairs; ask MFJ (mfjenterprises.com/pages/repairs) for the sketch.