Symptom: The LCD powers on, but you see black boxes or nothing.
Cause: You connected the LCD's V0 (contrast) pin to ground. The schematic shows a 10k potentiometer between GND and +5V, with the wiper going to V0.
Fix: Build the pot circuit. You need variable resistance to set the contrast.
The K3NG firmware generates a sidetone square wave on a digital pin (usually D6 or D9 via PWM). However, a raw square wave is harsh and weak. The schematic typically includes:
Pro Tip: Look for a zener diode (5.1V) clamping the audio line to protect the amplifier from voltage spikes. k3ng keyer schematic
Modern K3NG schematics use I2C LCDs. This requires only 4 wires:
Older schematics (pre-2015) use parallel 4-bit mode, which eats up 6 pins (RS, E, D4, D5, D6, D7). If you see a schematic with a 16-pin LCD connector and a potentiometer (10kΩ for contrast), that is a legacy parallel design. Avoid it unless you have the pins to spare. Symptom: The LCD powers on, but you see
Similar to keying, PTT requires a transistor switch. Many K3NG schematics dedicate a separate pin (e.g., D13) for PTT. This allows the keyer to put the radio into transmit mode before the first dit—essential for QSK (full break-in) or semi-break-in operation.
Schematic Note: Some advanced versions include a PTT delay circuit using an RC network (resistor + capacitor) to prevent hot-switching of relays. Pro Tip: Look for a zener diode (5
Before diving into the schematic, it is vital to understand the why. Traditional keyers (like the Bencher BY-1 or commercial Logikey) are locked into firmware. What you buy is what you get. K3NG wanted a keyer that could handle:
Because the code runs on an Arduino, the schematic is simply the wiring map to unlock these features. You can build a minimal keyer with three wires, or a deluxe command station with 40 components. The schematic scales with you.
