This Electronic canary circuit presented in this circuit diagramis a electronic door bell designed from an modified hartley oscillator with a couple of extra components included. The transformer is a small audio transformer center tapped with an impedance of 1Kohms at 1KHz and the secondary has an impedance of 8 ohms. The R2 and C4 give to this oscillator it's "chirp" sound.
Changing these components alters the frequency of the chirp.
The chirp of this electronic canary circuit is also voltage dependent. When the push button switch is operated the 100u capacitor is charged and when it's released, the oscillation decays and the chirp becomes faster.
|47K ¼Watt Resistor
100µF Electrolytic Capacitor