This is due to an indicator’s internal oscillator that can make for easier design implementation but reduces the range of tones and sounds that can be produced in comparison to transducers.Ī basic driver circuit for a piezo transducer can be composed of a reset resistor and an electronic switch, such as an FET or BJT, as shown in Figure 1.įigure 1. Basic driver circuit consisting of a reset resistor and electronic switchĮngineers can benefit from this circuit because it utilizes only a few, cost-effective parts, but is hindered by the power dissipation of the reset resistor and the reality of the voltage applied to the buzzer being restricted to the supply voltage (+V). As was noted earlier, transducers require an external excitation signal to operate, whereas indicator buzzers only need a supply voltage. But here is a brief overview of the technology before diving into driver circuit types.Ĭonstructed of a piezo material that physically deforms when a voltage is applied, piezoelectric devices produce more or less noise based on the amount of deformation caused by the applied voltage. To get a good primer on the working principles of buzzers and piezoelectric transducers, Buzzer Basics: Technologies, Tones, and Drive Circuits provides extensive information. There are a number of driver circuit options available to designers, and this article covers the advantages and disadvantages of several common design techniques. While this gives transducers added flexibility, it also results in additional design work surrounding the driver circuit, where the sound created by the buzzer is reliant upon both the selected buzzer and the signal used to drive it. It uses tone to play a variety of notes over a wide frequency range to test your sounder.Piezoelectric transducer buzzers are a well-known option for audible identification and alert between a product and its user, but unlike their indicator counterparts, transducer buzzers require an external driver circuit to produce a desired tone or sound. There is a simple melody sketch I adapted from Sparkfun to test the piezo sound quality and loudness reposited here. This is a super-small breakout useful for evaluation of the settings of the sounder driver for particular packaging constraints as well as a source for sound indication that can be easily incorporated into many existing projects. For many devices, users appreciate both visual feedback from led indicators, tactile feedback from switches and haptic motors, as well as aural feedback from something like this small piezo sounder. Or simply use this breakout board as part of your application to provide sound indication for users. The proper sound level for your application (which depends on the location within the design case, the case materials, place on the body or proximity to people, etc) can be determined with this breakout board and then hardwired into your custom design. The sound frequency drive is supplied to DIN by a GPIO pin from the MCU via PWM (tone). It has provision for driving the piezo at 1x, 2x, and 3x the input voltage (up to 3V3, a common MCU voltage) with simple TTL input from two GPIOs of the MCU. This NJU72501 sounder driver is a small solution to the problem of using piezo sounders well. Piezo sounders offer surprisingly high-quality sound in a small package, but require higher voltages than are typically available on 3V3 development boards to sound loud enough to hear well. When the project is small, as in wearable/portable, there are not a lot of good options that don't dominate the project size. Why did you make it?Īdding sound to a project is as easy as hooking up an 8-Ohm speaker to a PWM-capable GPIO pin (maybe with a current-limiting resistor!). Thus the sounder driver (maximum peak-to-peak drive +/-10 V in differential mode) and the sounder are well matched. The sounder operates between 0 and 10 kHz (midrange is 4 kHz) and at a maximum peak-to-peak voltage of +/- 12.5 V. I have included Murata's smallest (9 mm x 9 mm) PKMCS0909E4000 piezo sounder, but this can be left off the board if you want to use another piezo sounder. The board exposes all of the pins of the driver including VIN and GND for power, VOUT for the output of the boost converter, EN1 and EN2 to choose 0X, 1X, 2X, or 3X the input voltage (2.3 to 5.0V(1x/ 2x Mode), 2.3 to 3.4V(3x Mode)), and VO1 and VO2 to drive the piezo sounder either in single-ended mode (with VO1 connected to one piezo input and the other grounded) or differential mode (with both VO1 and VO2 connected to either input of the sounder). This is a small (0.7 " x 0.4 ") breakout board for New Japan Radio's NJU72501 piezo sounder driver.
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