| Loudspeakers are used to produce sounds. |
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How does it operate?
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PCB-mounted loudspeaker
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Case-mounted loudspeaker
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Loudspeakers convert an a.c. signal voltage into a sound. The signal voltage needs to have a frequency in the range 20 to 20,000 Hz (the range of frequencies that the human ear can hear).
Loudspeakers come in various forms. They can be mounted on the PCB or mounted on the case and attached to the PCB with flying leads. |
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Loudspeaker circuit – driven direct from
the process subsystem
Click on the circuit diagram to download a Livewire file of the circuit that you can investigate and add to your own circuit. |
PCB-mounted loudspeakers only need quite a small current. They can therefore be driven directly by PICs, 555 timers and most operational amplifiers.
The circuit on the left shows how the loudspeaker is connected in these cases.
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Loudspeaker circuit – driven by a transistor, Darlington driver or MOSFET
Click on the circuit diagram to download a Livewire file of the circuit that you can investigate and add to your own circuit |
For use with a CMOS IC, or if louder sound is needed, it is necessary to boost the current with a driver, such as a transistor, Darlington driver or MOSFET.
The circuit below shows how the loudspeaker is connected to the transistor in these cases.
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Possible applications
- Playing tunes with a PIC
- Part of a radio or other communication system
Making
Make sure that the subsystem providing the a.c. signal voltage to the loudspeaker is working correctly before adding the loudspeaker.
Loudspeakers with flying leads can be connected to the PCB using a terminal block.
A PCB-mounting terminal block
In the case of a PCB-mounted loudspeaker the position of the pads on the PCB needs to be adjusted to fit the pin spacing of the loudspeaker and allowance needs to be made for the size of the loudspeaker.
Testing
Send signal voltages of various frequencies to the loudspeaker and check that it responds.
Fault finding
If there is a fault, check that an a.c. signal voltage is coming into the loudspeaker.
Alternatives
- Piezo transducers do a very similar task. The uncased piezo transducer is cheaper than the PCB-mounted loudspeaker, but it only produces very quiet sounds. Most piezo transducers are slightly smaller than the PCB-mounted loudspeaker, but they are more expensive and produce poorer sound quality.
- Buzzers and piezo sounders can be used to produce a single tone. They are simple to use and require a d.c. signal voltage.
Web links
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