How often on average do
you have to call members of your family each day to tell them that
dinner is ready, it’s time to leave, and the like? The person you want
is usually in a different room, such as the hobby room or bedroom. A
powerful buzzer in the room, combined with a pushbutton at the bottom of
the stairs or in the kitchen, could be very handy in such situations.
The heart of this circuit is formed by IC1, a TDA2030. This IC has
built-in thermal protection, so it’s not likely to quickly give up the
ghost. R1 and R2 apply a voltage equal to half the supply voltage to the
plus input of the opamp. R3 provides positive feedback. Finally, the
combination of C2, R4 and trimmer P12 determines the oscillation
frequency of the circuit.
The frequency of the tone can also be adjusted using P1. There is no
volume control, since you always want to get attention when you press
pushbutton S1. Fit the entire circuit where you want to have the
pushbutton. The loudspeaker can then be placed in a strategic location,
such as in the bedroom or wherever is appropriate. Use speaker cable to
connect the loudspeaker. Normal bell wire can cause a signiﬁcant power
loss if the loudspeaker is relatively far away. The loudspeaker must be
able to handle a continuous power of at least 6 W (with a 20-V supply
The power quickly drops as the supply voltage decreases (P = Urms 2 /
RL). The power supply for this circuit is not particularly critical.
However, it must be able to provide sufficient current. A good nominal
value is around 400 mA at 20 V. At 4 V, it will be approximately 25 mA.
Most likely, you can find a suitable power supply somewhere in your
hobby room. Otherwise, you can certainly ﬁnd a low-cost power supply
design in our circuits archive that will ﬁll the bill!
Author: G. Baars
Copyright: Elektor Electronics