Some Arduino Code as used with the Left Coast Loafer CW Transmitter. //Turn ON: si5351.clock_enable(SI5351_CLK1, 1); //Turn OFF: si5351.clock_enable(SI5351_CLK1, 0); /*OK you missed it -- the "1" turns it on and the "0" turns it off.) So my code senses if Pin 4 is LOW and if so then turn ON the CLK1. If it is not LOW then turn it OFF. This is the standard If Else regime. You also have to blank out the frequency in the else part of the code. Here is the code*/ void CheckCW() { digitalRead(4); if(digitalRead(4) == LOW){ si5351.clock_enable(SI5351_CLK1, 1); si5351.set_freq( rx1 - 700, 0, SI5351_CLK1); ...