Basic CW keyer for an Arduino Nano. Written by Paul VK3HN, 7 Apr 2017.
A description and wiring diagram is at https://vk3hn.wordpress.com/Arduino-CW-keyer-for-a-BiTx-or-other-homebrew-rig This code may be duplicated, used, and hacked for hobby or experimental purposes. Please acknowledge the source (VK3HN) if you do.

Features:

• hard coded character weights
• hard coded or variable speed using a potentiometer
• two or more hard coded messages, with ability to interrupt playing messages
• straight key
• sidetone
• semi-break-in, PTT line to control transmit/receive switching, with configurable drop-out delay
• CW ident (sends hard-coded message (eg. callsign) every n seconds

The scripts assumes the following use of Nano IO lines:

D2 - keyed line, goes high with each key-down (dot or dash)
D3 - PTT line, goes high while transmitting, then reverts to low after BREAK_IN_DELAY mS (set to 300)
D4 - straight key (to GND) D8 - a square wave tone output at CW_TONE_HZ Hz (set to 700) D9 & 10 - Pushbuttons to earth for 2 (hardcoded) messages, you can add more D11 & D12 - paddle left and right, paddle center earthed A3 - Potentiometer wiper across 5v for keyer speed control.

You can connect an 8 ohm speaker to D8 with a 220 ohm series resistor for audible tone. To switch a relay or LED on the keyed or PTT lines, take D2/D3 to the gate of a 2N7000, 100k resistor from gate to earth, source to earth, drain to +12v via load (relay, LED with 220 ohm current limiting resistor).

All parameters are #define'd at the top and should be self-explanatory.

The script also provides a CW Ident, sends callsign every CW_IDENT_SECS seconds (set to 180).
To activate this feature, #define CW_IDENT.

NOTE: The master code includes enums -- these may generate compile time errros like these: key:42: error: variable or field ‘set_key_state’ declared void key:42: error: ‘key_state_e’ was not declared in this scope key:43: error: variable or field ‘activate_state’ declared void key:43: error: ‘trx_state_e’ was not declared in this scope variable or field ‘set_key_state’ declared void

A version without enums is on branch 'sans_enums' -- if you have problems compiling the master, use the code on this branch instead.

#Acknowledgment Hidehiko JA9MAT - thanks for suggesting addition of a 'straight key' mode, and for testing. Victor R3QX -- thanks for suggesting keyer memory playback interrupt (tap paddle or key).