Adjustable Duty Square Wave Generator

Built around the NE555 timer, this board produces a square wave with two potentiometers that set the frequency and the duty cycle, giving a ready-made pulse source without writing any code. A jumper selects one of four frequency bands, 1–50 Hz, 50 Hz–1 kHz, 1–10 kHz and 10–200 kHz, so it covers everything from slow LED blinking to fast clock signals. It runs from 5–15 V DC, and the output swings from about 4.2 V to 11.4 V peak-to-peak depending on the supply, with 15 mA available at 5 V and 35 mA at 15 V, enough to drive a MOSFET gate, motor driver or stepper driver step input. The two adjustments interact slightly, so set the frequency first and then fine-tune the duty cycle, ideally while watching the output on a scope or frequency meter.