The built-in speaker pin (Pin 8) is weak. The schematic can be extended to include an LM386 audio amplifier circuit. This adds a 10k pot for volume and a small speaker. Look for "K3NG Audio Filter" schematics.
Locate the 2N2222 transistor. Identify the Emitter (Arrow). Solder that to GND. Solder a 1k resistor from Pin 9 to the Base . Solder a wire from the Collector to your radio's "Tip" of the 3.5mm jack. Solder a separate GND wire to the "Sleeve" of the jack. k3ng keyer schematic
Put a red box around pins 20 & 21. You don't need them for basic functionality. The built-in speaker pin (Pin 8) is weak
The simplest schematic uses a USB cable (5V). For portable operation, you need an . Look for "K3NG Audio Filter" schematics
Some schematics show a 10kΩ resistor specifically for the straight key input (Pin 7). Straight keys are mechanical switches that bounce. The firmware handles debouncing, but the resistor ensures the logic level is valid. Section 3: The Output Stage – Don't Fry Your Arduino The biggest mistake new builders make is connecting Pin 9 (Key Out) directly to their radio's "CW Key" jack.
Whether you are printing the k3ng_keyer_schematic.pdf to build a contest-grade station or just to understand how interrupts work, this design represents the pinnacle of DIY radio culture.
Solder two 4.7k resistors from pins 2 and 3 to +5V. Solder your left paddle wire to Pin 2. Right paddle to Pin 3.