An interesting circuit of a bicycle horn based on a popular, low cost
telecom ringer chip is described here. This circuit can be powered using
the bicycle dynamo supply and does not require batteries, which need to
be replaced frequently. The section comprising diodes (D1 and D2) and
capacitors (C1 and C2) forms a half-wave voltage-doubler circuit. The
output of the voltage doubler is fed to capacitor C3 via resistor R1.
The maximum DC supply that can be applied to the input terminals of IC1
is 28V. Therefore zener diode ZD1 is added to the circuit for protection
and voltage regulation. The remainder of the circuit is the tone
generator based on IC1 (KA2411).
The
dual-tone output signal from pin 8 of IC1 is fed to the primary of
transformer X1 (same as used in transistor radios) via capacitor C6. The
secondary of X1 is connected to a loudspeaker directly. In case you are
interested in connecting a piezoceramic element in place of the
loudspeaker, remove capacitor C6, transformer X1, and the loudspeaker.
Connect one end of the piezoceramic disk to pin 5 of IC1 and the other
end to pin 8 of IC1 through a 1/4W, 1-kiloohm resistor. IC1 KA2411 is
also available in COB style, with the same pin configuration. Both
packages work equally well.
However,
to get the best results with the COB package, change values of
resistors R2 through R4 to 330-kilo-ohm, capacitor C4 to 0.47µF, 63V
electrolytic (positive end to pin 3 of IC1), and C5 to 0.005µF, 63V.
This bicycle horn project can also be used as a telephone extra ringer
by just removing all components on the left side of capacitor C3 and
connecting the circuit shown in Fig. 2 to the terminals of capacitor C3.
The
dual-tone output signal from pin 8 of IC1 is fed to the primary of
transformer X1 (same as used in transistor radios) via capacitor C6. The
secondary of X1 is connected to a loudspeaker directly. In case you are
interested in connecting a piezoceramic element in place of the
loudspeaker, remove capacitor C6, transformer X1, and the loudspeaker.
Connect one end of the piezoceramic disk to pin 5 of IC1 and the other
end to pin 8 of IC1 through a 1/4W, 1-kiloohm resistor. IC1 KA2411 is
also available in COB style, with the same pin configuration. Both
packages work equally well.
However,
to get the best results with the COB package, change values of
resistors R2 through R4 to 330-kilo-ohm, capacitor C4 to 0.47µF, 63V
electrolytic (positive end to pin 3 of IC1), and C5 to 0.005µF, 63V.
This bicycle horn project can also be used as a telephone extra ringer
by just removing all components on the left side of capacitor C3 and
connecting the circuit shown in Fig. 2 to the terminals of capacitor C3.
