Place a 1N4148 diode in reverse parallel across the output side (collector/emitter) of the optocouplers to protect against inductive spikes from older rigs. 5. Audio Sidetone Generation
Using a standard 16x2 LCD display via an I2C backpack reduces the necessary wire count from sixteen down to four. Connect to Arduino pin A4 . SCL (Clock Line): Connect to Arduino pin A5 .
If you are translating this repacked schematic into a custom Printed Circuit Board (PCB) using software like KiCad or EasyEDA, keep these design principles in mind:
To repack this efficiently, visualize the circuit in four distinct blocks. This prevents "wiring spaghetti" inside your enclosure. 1. The Logic Brain k3ng keyer schematic repack
Use a metal "mint tin" or aluminum project box to prevent RF interference from tripping the Arduino.
Connect a 10k Ω linear potentiometer. Pin 1 goes to 5V , Pin 2 (wiper) goes to Analog Pin A0 , and Pin 3 goes to GND . This allows real-time WPM adjustments.
If you need help tailoring this project further, let me know: Place a 1N4148 diode in reverse parallel across
Updated sidetone circuit with a simple R/C filter to smooth out those "fierce" harmonics often found in basic piezo setups. Modular Inputs:
The repack has a first page matrix: “If you have I2C LCD → See Section 4, Figure 4.2” . Section 4 shows Nano pins A4 (SDA) and A5 (SCL) going to LCD backpack. No additional pins needed.
: Typically uses an optoisolator (e.g., 4N25) or a switching transistor (2N2222) with a 100-ohm base resistor and a small ceramic capacitor (0.01uF) to prevent RF interference. Connect to Arduino pin A4
The repack includes a final checklist: solder all GND connections, check for shorts, upload firmware with matching pin defines, and test with a dummy load or LED across the key output.
: A simple piezo speaker glued to the enclosure base provides clear audio feedback for practice. 2. Strategic "Repacking" Tips