Batteryless wireless transmission system for electronic drum uses piezoelectric generator for play signal and power source

Transcription

1 Journal of Physics: Conference Series PAPER OPEN ACCESS Batteryless wireless transmission system for electronic drum uses piezoelectric generator for play signal and power source To cite this article: H Nishikawa et al 2015 J. Phys.: Conf. Ser Related content - Fish scales act as piezoelectric generator - In Vivo Batteryless Wireless Communication System for Bio-MEMS Sensors Tomohiro Yamada, Takumi Uezono, Kenichi Okada et al. - Energy Storage Characteristics of a Piezo- Generator using Impact Induced Vibration Mikio Umeda, Kentaro Nakamura and Sadayuki Ueha View the article online for updates and enhancements. This content was downloaded from IP address on 21/12/2017 at 19:08

2 Batteryless wireless transmission system for electronic drum uses piezoelectric generator for play signal and power source H. Nishikawa, A. Yoshimi, K. Takemura, A. Tanaka, and T. Douseki Ritsumeikan University, Graduate School of Science and Engineering , Noji-Higashi, Kusatsu, Shiga, Japan Abstract. A batteryless self-powered wireless transmission system has been developed that sends a signal from a drum pad to a synthesizer. The power generated by a piezoelectric generator functions both as the Play signal for the synthesizer and as the power source for the transmitter. An FM transmitter, which theoretically operates with zero latency, and a receiver with quick-response squelch of the received signal were developed for wireless transmission with a minimum system delay. Experimental results for an electronic drum without any connecting wires fully demonstrated the feasibility of self-powered wireless transmission with a latency of 900 µs. 1. Introduction One problem with the plethora of electronic instruments in the music world today is all the wires and cables that need to be transported, plugged in, and managed. A conventional electronic drum set employs wires to connect the sensing pads to the synthesizer unit. The wires complicate setup and look messy, and the difficulty of assembly and disassembly limits use of such a drum set to one fixed place. A wireless system, on the other hand, would provide portability and greatly expand the range of venues where electronic drums could be used in place of acoustic ones. A batteryless wireless FM transmitter, which uses the output of a piezoelectric generator both as a power source and to produce an analog signal, has been developed. An FM receiver with an ultrafast squelch that operates with almost zero latency helps reduce the system delay in a wireless electronic drum (Fig.1). Figure 1. (a) New wireless drum system and (b) Conventional electronic drum system with connecting wires. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by Ltd 1

3 2. Basic Theory The drum pad of an electronic drum contains a piezoelectric sensor [1]. When the pad is hit with a drumstick, the vibration propagates to the piezoelectric sensor, which produces an electrical signal. In a conventional system, the signal is sent over a wire to a synthesizer, which produces the appropriate sound. In our newly developed wireless system, a piezoelectric generator was mounted in a Styrofoam housing, covered with a protective silicone sheet (to protect it from strikes with a drumstick), and placed in a drum pad (Fig. 2). When the pad is struck, the force is conducted to the generator, and electrical energy is produced. The generated signal drives a transmitter, which sends a modulated signal wirelessly to a receiver in the synthesizer. This is in contrast to a conventional system, which sends the signal to the synthesizer over a wire (dotted line in Fig. 3). Figure 2. Electronic drum pad with piezoelectric generator: (a) photograph and (b) crosssectional diagram. Figure 3. Block diagram of self- powered wireless electronic drum The energy produced by the piezoelectric generator is used both for the Play signal sent to the synthesizer and as a power source [2] for the wireless transmitter to support batteryless operation. A full-wave-rectifier circuit with a diode bridge is placed between the generator and the transmitter. Since the ground of the transmitter is taken to be the DC reference, the negative swing of the generator output is inverted to a positive swing by the rectification of the diode bridge. Thus, DC isolation is required between the drum signal and the power circuitry so that a proper signal with both positive and negative polarities can be sent to the transmitter for modulation. In this study, that was accomplished by placing a transformer with appropriate coupling capacitors between the generator and transmitter (Fig. 4). 2

4 Figure 4. Block diagram of DC isolation, which drives power generated by piezoelectric generator into power source Vcc) and analog signal for transmission (Vsig). For percussion instruments, such as drums, the maximum acceptable latency in the signal transmission process has been empirically estimated to be 1 ms. A digitally modulated radio signal is widely used for wireless microphones [3][4] and other equipment because there is no significant distortion where latency is not a major concern. For a drum system, however, a small latency has a higher priority than good sound quality; and thus, an analog FM modulation architecture, which theoretically provides zero latency, was selected for our system. Although the latency is zero in the wireless process, the charge-up time of the rectification in the transmitter and the squelch response in the receiver are the main components of the total delay of the system (Fig. 5). The values of the decoupling and filtering capacitors in the rectification and regulation circuit of the transmitter (in Fig. 4) must be reduced to the minimum values needed to obtain a quick charge-up time. A high-speed squelch is required to obtain a short enough recovery time from the shut-down mode in the FM receiver (Fig.6). Figure 5. Relationship among pad output, rectified power source, transmitted signal, squelch response, and received signal. Figure 6. Block diagram of FM receiver with high-speed squelch. 3

5 3. Fablication and experiments The FM transmitter, which includes DC isolation, rectifiers, and a regulator, is constructed on a small printed circuit board measuring 2.3 cm 3.5 cm. A plug on the transmitter board connects the input line to the drum pad. All of the receiver functions, including the quick-response squelch, are implemented on a printed circuit board measuring 8.7 cm 5.6 cm (Fig. 7). Figure 7. Photographs of (a) 315-MHz batteryless FM transmitter, and (b) receiver board with embedded highspeed squelch. The rectified regulated DC power was measured at the output of the regulator, to which a 1.2-kΩ resistor was connected to simulate the load of the FM transmitter. The required charge-up time to reach a stable 1.8-V DC level was 500 µs. The output of the regulator remained 1.8 V for more than 2 ms, which is enough power for the transmitter to maintain oscillations and modulation (Fig. 8). Figure 8. Measured waveforms: input from piezoelectric generator (Vin), and rectified DC (Vcc). The response time of the squelch in the FM receiver was measured (Fig. 9). The squelch gate opens right after a 315-MHz carrier is supplied to it. The squelch response time is almost zero. 4

6 Figure 9. Measured waveform of received carrier (top) and squelch response (bottom). Experiments were performed by attaching the transmitter to a drum pad and connecting the receiver to a synthesizer (Fig. 10a). The transmitter input and the receiver output were monitored on an oscilloscope, and the waveforms (Fig. 10b) were found to be in good agreement. The latency was 900 µs, which meets the target specification of 1 ms. Thus, it has been demonstrated that a batteryless FM transmission system is applicable to an electronic drum, and that the latency is sufficiently small. Figure 10. (a) Setup (drum pad, transmitter, receiver, synthesizer) for evaluating self-powered FM transmission system for electric drum, (b) Measured waveform of pad output and signal received at synthesizer after wireless transmission. 4. Conclusion A batteryless self-powered wireless transmitter has been developed that sends a signal from a drum pad to a synthesizer. The power generated by a piezoelectric generator functions both as the Play signal for the synthesizer and as the power source for the wireless transmitter. A DC isolation technique based on a transformer and coupling capacitors provides efficient power division. The system employs direct FM modulation so that it theoretically provides zero latency in the wireless transmission process. The latency of the whole system, including power rectification, the startup of the FM transmitter, and the receiver response, is 900 µs, which is small enough for an electronic drum. References [1] Electronic Drums [Online]. Available at [2] S. Wang, et.al., Energy harvesting with piezoelectric drum transducer, Applied Physics Letters 90, , [3] Wireless Microphone System [Online]. Available at [4] Digital Signal Processing in RF Applications [Online]. Available at Web-versions/Schilcher-1.pdf pp. 1-3,