|Piezo transducers are used to produce sounds.
How does it operate?
PCB-mounted piezo transducer
Piezo transducer with flying leads
Uncased piezo transducer
Piezo transducers 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).
Piezo transducers come in various forms. They can be mounted on the PCB or attached with flying leads. The cheapest piezo transducer is uncased but this produces very quiet sounds.
It is important not to confuse piezo transducers with piezo sounders or piezo indicators. These behave in the same way as buzzers. They have a built in oscillator and are switched on by a d.c. signal voltage.
Piezo transducer 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
The current consumption of piezo transducers is quite low – typically 5 to 10 mA.
They can therefore be driven directly by PICs 555 timers and most operational amplifiers.
The circuit on the left shows how the piezo transducer is connected in these cases. The symbol used in the circuit diagram for the piezo transducer is in fact a loudspeaker symbol – there is no symbol for a piezo transducer available in Livewire.
Note that the piezo transducer needs to be connected the right way round – with the negative lead to the 0V line.
Piezo transducer 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.
The current needed is too large to be reliably provided by a CMOS IC.
In that case it is necessary to boost the current with a driver, such as a transistor, Darlington driver or MOSFET.
The circuit below shows how the piezo transducer is connected to the transistor in these cases.
Note that the piezo transducer needs to be connected the right way round – with the positive lead to the +Vs line.
- Playing tunes with a PIC
- Part of a radio or other communication system
Make sure that the subsystem providing the a.c. signal voltage to the piezo transducer is working correctly before adding the piezo transducer.
Piezo transducers with flying leads can be connected to the PCB using a terminal block.
Make sure that the piezo transducer is connected the right way round.
A PCB-mounting terminal block
In the case of PCB-mounted piezo transducers the position of the pads on the PCB needs to be adjusted to fit the pin spacing of the transducer and allowance needs to be made for the size of the transducer.
Send signal voltages of various frequencies to the piezo sounder and check that it responds.
If there is a fault, check that an a.c. signal voltage is coming into the piezo transducer. Check that the piezo transducer is connected the right way round.
- Small PCB-mounted loudspeakers do a very similar task. They are cheaper than most piezo transducers (apart from the uncased version) and produce a better sound quality. They are slightly larger than most piezo transducers.
- Buzzers and piezo sounders can be used to produce a single tone. They are simple to use and require a d.c. signal voltage.
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