Look for pull-up resistors (4.7kΩ to 10kΩ) on the paddle inputs. Without these, the pins float, causing random keying.
The heart of the schematic is the ATMega328P (on Nano/Uno) or ATMega2560 (on Mega). The key pins to identify are: k3ng keyer schematic
Option B — Optocoupler (isolation):
"It supports LCDs, PS2 keyboards, potentiometers for speed control... hell, it even speaks in Morse if you want it to," Silas explained. "But the core schematic is simple. You have inputs for your paddles, outputs for your rig, and a few resistors to keep things polite." Look for pull-up resistors (4