Hi everyone! I’m sharing a classic Relay Oscillator Circuit designed to continuously toggle an external output between VCC and GND.

Unlike a standard timer, this circuit features a clever feedback loop connected to the relay's internal switches (K1).

How it works:

• The Charging Phase: When power (VCC) is applied, the C1 (220uF) capacitor charges through R1 (4.7kohm).
• The Trigger: As soon as the voltage is high enough, it triggers the NPN power transistor Q2 (BD435) through R2 (2.2kohm), activating the relay coil.
• The Feedback Loop: When the relay switches, the internal contact connected back to the RC network alters the capacitor's state (discharging it or cutting the latch). This immediately turns off the transistor, releasing the relay and restarting the whole cycle.
• Protection: A 1N4004 (D1) flyback diode is placed across the coil to suppress voltage spikes and protect the transistor.
• Output: The result is a continuous, automated switching wave at the OUT terminal block, perfect for flashing lights, automated testing, or cycling loads.

You can easily adjust the oscillation frequency (speed of the switching) by experimenting with different values for C1 and R1.

Feel free to download the Gerber files and let me know your thoughts in the comments!