Nuts and Volts - November 2010

supplied with the kit available in the Nuts & Volts webstore.

Figure 7 shows the speaker and circuit ready to go. I used an iPod for the audio source for the circuit. (The iPod is NOT included in the kit.)

Construction

■ FIGURE 5. Schematic of piezoelectric speaker project.

speaker measures three inches by six inches.

While the material does change dimensionally across its length, it is to a lesser degree as the dipoles are mostly aligned perpendicular to its thickness.

To use this material as a speaker, it is necessary to provide a high voltage audio signal. This is accomplished by feeding a standard audio signal through a step-up transformer.

Referring to the schematic in Figure 5, an electrical audio signal from a radio or iPod is applied to the input header P1. The signal feeds through a voltage divider network composed of resistor R4 and potentiometer V1. The signal from V1 feeds into the LM386 audio amplifier IC. V1 acts as a volume control. The LM386 is set up in a standard configuration to produce a gain of 50X amplification.

The output of the audio amplifier is fed to the primary of a mini step-up transformer. The high voltage output from the transformer is fed to the piezoelectric film speaker.

Figure 6 is a close-up of the circuit built on a PCB Mount and solder the HV transformer making sure to line up the yellow dot on the transformer to the silkscreen dot on the transformer outline. Mount and solder (V1) 10K potentiometer PC mount (R3 and R4) 390 ohm 1/4 watt resistor; R1 1.2K ohm 1/4 watt resistor; R2 10 ohm 1/2 watt resistor; C1 and C4, 10 µF capacitors; C2, .047 µF capacitor; and C3, a 200-250 µF capacitor. Mount and solder slide switch S1. The input P1 and piezo speaker outputs are two-pin female sockets. Mount and solder into place. Plug the LM386 in the eight-pin socket. Orientate the indent on the IC to the indent on the silkscreen.

Usage

Connect your audio source to the input header. Turn it on and set its volume range mid-point. Connect the piezoelectric film speaker to the output. Turn on the circuit and adjust the V1 volume control until you hear sound coming out of the speaker.