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

• 1× M3×20 socket head screw (key stop), 5× M3 plain nuts (DIN 934)

• 1× M3 washer — amazon.com/dp/B0DP6ZB4DD

• 2× M3×6 set screws (speaker), 4× M2×6 self-tapping screws (board)

• 1× brass round-head paper fastener, Ø10 head (fixed contact)

• 1× ring solder lug, size 3.2 (moving contact) — amazon.com/dp/B0C53DX4DT

• 4× Ø10 mm self-adhesive rubber feet

Cable and programming

• Digirig audio/PTT cable for your radio — https://digirig.net

• FTDI FT232R USB-serial adapter set to 3.3 V, for firmware upload

The full BOM with schematic references is BOM.md inside MCW-Generator-source.zip.

keyer-lid-with-labels.3mf has the lid and labels already combined as one object with two parts, for any slicer. MCW-Generator-Bambu-project.3mf is the Bambu Studio project: two plates with every part placed, filaments assigned, and fuzzy skin painted on the outer walls and the cover top.

Print settings

• Material: PLA or PETG. Dark for base, lid and cover; translucent (natural/clear) for the labels.

• Infill: 100 %.

• Layer height: 0.2 mm. The panel lettering is engraved 0.6 mm deep, three 0.2 mm layers, so the labels inlay prints cleanly at that height.

• Supports: base only.

• The fastener holes are sized for self-tapping M2/M3 screws straight into plastic; no heat-set inserts.

Assembly

Step-by-step assembly (12 steps), firmware upload, and the configuration table are in README.md inside MCW-Generator-source.zip. The one-page user manual is MCW-Generator-manual.pdf.