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Optocoupler / Transistor PTT Keyer Board

A small opto-isolated or transistor PTT keyer takes a logic output (Pi GPIO, CM108 GPIO, or serial RTS/DTR) and switches the radio's PTT line to ground, while electrically isolating the radio from the node computer. Why it matters: Driving a radio PTT directly from a 3.3V Pi pin risks ground loops, level mismatches, and back-EMF damage. An opto keyer isolates the two grounds (a frequent cure for hum) and safely sinks the PTT current. Include a flyback diode if switching anything inductive. Use: Wire the logic input to your control output and the output to the radio's active-low PTT line. Pairs naturally with the basic-mobile and HT radio entries that need an external PTT driver.