MCW Generator — Morse keyer with built-in straight key for any FM radio

The MCW Generator sends Morse code as an audio tone through a transceiver's audio input, the way modulated CW (MCW) works on FM. It plugs into the radio with a stock Digirig audio/PTT cable and keys the radio's PTT itself.

Video: https://www.youtube.com/shorts/aYVKpifshzY

This is not a CW keyer in the usual sense. The transmitter sends an FM signal carrying a tone, not a bare carrier. The station at the other end hears it as a tone on FM and replies the same way.

Features

- straight key built into the lid, with adjustable gap and magnetic return

- four message keys on a membrane keypad (CQ call etc., set in the firmware)

- 700 Hz sine tone with 4ms rise and fall; software debounce on the key

- break-in: PTT keys instantly, the transmitted tone starts 0.5 s later so the radio is settled; PTT drops 1 s after the last element

- local sidetone and received audio on a built-in speaker, each with its own volume knob

- LEDs for power, key down and PTT; backlit panel labels when printed in translucent filament

- 3.5 mm TRRS socket wired to the Digirig pinout, so the off-the-shelf Digirig cable for your radio fits

- 2×AA cells; sleeps after 15 min idle, the key or a keypad press wakes it

- hinged cover held shut by magnets protects the key and knobs in a bag

Electronics: Arduino Pro Mini 3.3 V / 8 MHz, PAM8302A amplifier, one NPN transistor for PTT, and a handful of passives on a 60 × 40 mm protoboard. The full schematic, firmware, parts list and a one-page user manual are in MCW-Generator-source.zip.

Closed size 80 × 110 × 75 mm.

Purchased parts

Electronics

- 1× Arduino Pro Mini 3.3 V / 8 MHz (ATmega328P), regulator bypassed, LEDs removed — amazon.com/dp/B08LNBYLBT

- 1× PAM8302A 2.5 W class-D amplifier module (remove its 1 kΩ SD pull-up) — amazon.com/dp/B0H3467G81

- 1× 2N2222 or 2N3904 NPN transistor

- Resistors: 6× 1 kΩ, 3× 10 kΩ, 1× 100 kΩ

- 1× 10 kΩ 3296W trimmer (TX deviation) — amazon.com/dp/B0CC91M338

- Capacitors: 1× 100 µF electrolytic, 6× 100nF

- 1× 60 × 40 mm protoboard (56 × 36 mm mounting holes)

- 1× 5-pin 2.54 mm header for the keypad ribbon — amazon.com/dp/B0774VBJ3J

Panel

- 1× KCD11 rocker switch, 15 × 10 mm

- 2× 10 kΩ potentiometer, 16 mm body, M7 bushing, with 15 mm knobs — amazon.com/dp/B0D6WB7SZJ

- 1× 3.5 mm TRRS panel jack, 7 mm bushing — amazon.com/dp/B00OGLEE4C

- 1× 1×4 membrane keypad, 70 × 20 mm, 5-pin ribbon — amazon.com/dp/B0C4H495MB

- 1× 35 × 25 × 6.8 mm 4 Ω 3 W speaker — amazon.com/dp/B0FM3QN15Q

- 3× 5 mm LEDs (blue, green, red) in 8 mm panel holders — amazon.com/dp/B08G4X5WBT

- 1× set 2×AA contact plates, plus 2× AA cells — amazon.com/dp/B0GSTX7762

Key and enclosure hardware

- 2× 698 bearings (8 × 19 × 6 mm) — amazon.com/dp/B0CRDZBXKH

- 2× Ø10 × 3 mm magnets (key return)

- 2× Ø6 × 3 mm magnets (cover latch) — amazon.com/dp/B0GVLJNTBV

- 4× M3×10 countersunk screws, plain steel , not stainless (the cover magnets grip the front two); M3 countersunk assortment — amazon.com/dp/B0GFDHNDM1

- 2× M3×35 socket head screws (cover hinge) — amazon.com/dp/B0FS1Q1QHC

- 3× M3×12 socket head screws (key pivots, knob) — amazon.com/dp/B0FKM7JGQ4