A self-sustaining square wave oscillator built on a custom 2-layer PCB, designed in EasyEDA. Two BC547 transistors alternate switching states, driving blinking LEDs — no external trigger required.
The astable multivibrator uses the charge and discharge cycle of capacitors through resistors to continuously toggle two transistors. Neither transistor has a stable resting state — the circuit oscillates forever.
With R = 10kΩ & C = 10µF → f ≈ 7.2 Hz
Q1 turns ON → collector goes LOW → C1 pulls Q2 base negative, switching Q2 OFF
C2 charges through R3 until Q2's base crosses threshold → Q2 switches ON
Q2 ON forces Q1 OFF. Capacitors reverse-charge → cycle repeats indefinitely
| Component | Value / Part | Qty | Function |
|---|---|---|---|
| NPN Transistor | BC547 | ×2 | Core switching elements — alternately saturate and cut off to produce oscillation |
| Resistor | 1 kΩ | ×2 | Collector load — limits LED current and sets collector voltage swing amplitude |
| Resistor | 10 kΩ | ×2 | Base timing resistors — define RC constant and output oscillation frequency |
| Electrolytic Cap | 10 µF / 25V | ×2 | Timing capacitors — charge through resistors to drive alternating base switching |
| LED | Red 5mm | ×2 | Visual output — blink alternately at the oscillation frequency (~7 Hz) |
| Power Supply | 5V DC | ×1 | Regulated supply via onboard 2-pin header or micro-USB breakout board |
Schematic files, PCB layout, Gerber outputs, and full documentation are available in the public repository.