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* CW Keyer
* The CW keyer handles either a straight key or an iambic / paddle key.
* They all use just one analog input line. This is how it works.
* The analog line has the internal pull-up resistor enabled.
* When a straight key is connected, it shorts the pull-up resistor, analog input is 0 volts
* When a paddle is connected, the dot and the dash are connected to the analog pin through
* a 10K and a 2.2K resistors. These produce a 4v and a 2v input to the analog pins.
* So, the readings are as follows :
* 0v - straight key
* 1-2.5 v - paddle dot
* 2.5 to 4.5 v - paddle dash
* 2.0 to 0.5 v - dot and dash pressed
* The keyer is written to transparently handle all these cases
* Generating CW
* The CW is cleanly generated by unbalancing the front-end mixer
* and putting the local oscillator directly at the CW transmit frequency.
* The sidetone, generated by the Arduino is injected into the volume control
// in milliseconds, this is the parameter that determines how long the tx will hold between cw key downs
#define CW_TIMEOUT (600l)
#define PADDLE_DOT 1
#define PADDLE_DASH 2
#define PADDLE_BOTH 3
//we store the last padde's character
//to alternatively send dots and dashes
//when both are simultaneously pressed
char lastPaddle = 0;
//reads the analog keyer pin and reports the paddle
byte getPaddle(){
int paddle = analogRead(ANALOG_KEYER);
if (paddle > 800) // above 4v is up
return 0;
if (paddle > 600) // 4-3v is dot
else if (paddle > 300) //1-2v is dash
return PADDLE_DOT;
else if (paddle > 50)
return PADDLE_BOTH; //both are between 1 and 2v
return PADDLE_STRAIGHT; //less than 1v is the straight key
* Starts transmitting the carrier with the sidetone
* It assumes that we have called cwTxStart and not called cwTxStop
* each time it is called, the cwTimeOut is pushed further into the future
void cwKeydown(){
keyDown = 1; //tracks the CW_KEY
tone(CW_TONE, (int)sideTone);
digitalWrite(CW_KEY, 1);
cwTimeout = millis() + CW_TIMEOUT;
* Stops the cw carrier transmission along with the sidetone
* Pushes the cwTimeout further into the future
void cwKeyUp(){
keyDown = 0; //tracks the CW_KEY
digitalWrite(CW_KEY, 0);
cwTimeout = millis() + CW_TIMEOUT;
* The keyer handles the straight key as well as the iambic key
* This module keeps looping until the user stops sending cw
* if the cwTimeout is set to 0, then it means, we have to exit the keyer loop
* Each time the key is hit the cwTimeout is pushed to a time in the future by cwKeyDown()
void cwKeyer(){
byte paddle;
lastPaddle = 0;
paddle = getPaddle();
// do nothing if the paddle has not been touched, unless
// we are in the cw mode and we have timed out
if (!paddle){
if (0 < cwTimeout && cwTimeout < millis()){
cwTimeout = 0;
keyDown = 0;
if (!cwTimeout)
//if a paddle was used (not a straight key) we should extend the space to be a full dash
//by adding two more dots long space (one has already been added at the end of the dot or dash)
if (cwTimeout > 0 && lastPaddle != PADDLE_STRAIGHT)
delay(cwSpeed * 2);
// got back to the begining of the loop, if no further activity happens on the paddle or the straight key
// we will time out, and return out of this routine
// if we are here, it is only because the key or the paddle is pressed
if (!inTx){
keyDown = 0;
cwTimeout = millis() + CW_TIMEOUT;
// star the transmission)
// we store the transmitted character in the lastPaddle
if (paddle == PADDLE_DOT){
lastPaddle = PADDLE_DOT;
else if (paddle == PADDLE_DASH){
delay(cwSpeed * 3);
lastPaddle = PADDLE_DASH;
else if (paddle == PADDLE_BOTH){ //both paddles down
//depending upon what was sent last, send the other
if (lastPaddle == PADDLE_DOT) {
delay(cwSpeed * 3);
lastPaddle = PADDLE_DASH;
lastPaddle = PADDLE_DOT;
else if (paddle == PADDLE_STRAIGHT){
while (getPaddle() == PADDLE_STRAIGHT)
//introduce a dot long gap between characters if the keyer was used
if (lastPaddle != PADDLE_STRAIGHT)