Feeling chirpy? Attract new friends with this modified hartley oscillator. You could also use it as a replacement
doorbell.
Notes:
This circuit is a modified hartley oscillator with a
couple of extra components included. The transformer is a small audio
transformer, type LT700. The primary is center tapped with an impedance of
1Kohms at 1KHz . The secondary has an impedance of 8
ohms. The inclusion of R1 and C1 give this oscillator its characteristic
"chirp". As the 100u capacitor charges via the 4.7K resistor, R1 the
bias for the transistor is cut off. This causes the oscillation to stop, the
capacitor discharges through the base emitter circuit of the transistor and
oscillations start again. Altering these components alters the frequency of the
chirp. The chirp is also voltage dependent. When the push button switch is
operated the 100u capacitor is charged. When its
released, the oscillation decays and the chirp becomes faster.
Return to Music & Special Effects