The basic idea of active noise control was first proposed by the German physicist Paul Lueg when he invented the "electronic silencer" in 1936. Compared with traditional passive control, active noise control technology has obvious effect on middle and low frequency band noise control, lightweight system and strong real-time performance, and has potential application value.
Noise control is a real-time control, which requires a large amount of computation. It is difficult to achieve with a single-chip computer. In the 1980s, the advent of Digital Signal Processing (DSP) chips has opened up a broad space for the real-time control of signals. With the maturity and development of chip technology, DSP has become a component of modern smart controller.
This paper uses the DSP chip TMS320F2812 to design an intelligent controller, which can run independently offline and simulate online through the USB interface. The active intelligent control system of automobile internal noise is designed based on the controller.
Circuit Design of Intelligent Control System
1 Design process and system diagram
The design process of an intelligent control system for automobile internal noise is shown in Fig. 1.
Figure 1 Flowchart of hardware design for DSP intelligent controller
When selecting devices, consideration should be given to the matching between devices, as well as the supply capability and technical support of the devices. The performance of the DSP chip TMS320F2812 selected in this design is as follows: Using high performance static CMOS low power design technology, the main frequency is up to 150MIPS (clock cycle 6.67ns), supporting JTAG boundary scan interface; High efficient 32-bit high CPU; And up to 128K × 16 FLASH memory, etc.
The design of printed circuit board requires the knowledge of transmission line theory, wiring technology and system structure design to ensure the integrity of the signal. In addition, the electromagnetic interference and compatibility issues are emphasized.
As shown in Figure 2, the intelligent controller is mainly composed of analog circuit (including digital signal acquisition circuit and output signal processing circuit), DSP subsystem (including DSP chip and peripheral circuit), power supply, clock and reset circuit. The following describes the design of several main circuits.
Figure 2 Smart controller architecture block diagram
Figure 3 Power supply and reset circuit
2 Power supply and reset circuit design
The performance of power supply (such as ripple, power-on sequence, etc.) is required by the DSP system, so the linear piezoelectric circuit chip TPS767D301 is selected in this design. TPS767D301 is a dual output low leakage voltage regulator. It has the following characteristics: Each power output has a separate reset and output enable control; It has fast transient response function. Voltage output is 3.3V/1.8V adjustable.
The power supply circuit composed of TPS767D301 introduces a + 5V voltage from an external regulator power supply, and the output voltage of the + 5V voltage after TPS767D301 is 1.8V and 3.3V. To reduce the interference of the power supply itself to the DSP, a filter network is added to the circuit, as shown in Figure 3.
3 A/D, D/A Circuit Design
The TMS320F2812 chip has a 12-bit ADC with a conversion frequency of 25 MHz. Its front-end is two 8-choice-1 multiplexers and two simultaneous sampling/holders. When the requirements are not very high, it can be used to construct a synchronous sequential sampling circuit or to construct a synchronous sampling after adding an external sample holder. Considering the high requirement of the system for power collection and speed, the external 6-channel 16-bit ADC ADS8364 is selected in the sampling module. Inside the device, there are six high-speed sample-hold amplifiers, six high-speed ADCs, a reference voltage source and three reference voltage buffers, which can provide a synchronous sampling rate of 250KSPS, as well as a conversion of all six input channels with ultra-low power consumption (69mW/per channel), which results in lower unit cost for all channels. The data output interface voltage of 6 channels is between 2.7 and 5.5V, which makes it easy to interface directly with DSP and eliminates the intermediate level conversion. Six fully independent ADCs can greatly improve the overall parallel processing speed of the hardware, and still guarantee superior common mode suppression over 80dB at 50kHz input signal. They are especially suitable for high interference environments. Figure 4 shows the interface circuit between ADS8364 and TMS320F2812.
In order to achieve the control function of the system, four 12-bit voltage output DAC TLV5614 is selected in the D/A conversion circuit. It has a flexible four-line serial interface and can be seamlessly connected with the TMS320 SPI, QSPI and Mcrowire serial ports. The programming control of TLV5614 consists of 16-bit serial words, which are two DAC addresses, two separate DAC control bits, and 12-bit DAC input values. The device is powered by dual power supply: a set of digital power supply for serial interface, namely DVDD and DGND; The other is the analog power supply used for the output buffer, AVDD and AGND. The two groups of power supply are independent and can be any value between 2.7 and 5.5V. The advantage of dual power application is that DAC works with 5V power supply, while the digital part of DAC works with 2.7-5.5V power supply and can be connected to multiple interfaces.
Figure 4 Interface circuit between ADS8364 and TMS320F2812
Figure 5 TLV5614 interface circuit
In the design, the D/A circuit uses a reference voltage of 2.5V. To control D/A conveniently, the GPIOB of TMS320F2812 is used as the control line of the conversion chip. The circuit is shown in Fig. 5.
4 External SRAM, FLASH Extended Circuit Design
Because the control system needs to store a large amount of data for analysis and utilization, according to the principle of "zero wait" between DSP and external memory, the external memory of F2812 is extended by IS61LV6416-12T, which is 64K by IS61LV6416-12T. × 16 high speed CMOS SRAM, 3.3V power supply, and its interface circuit with TMS320F2812 is shown in Figure 6.
Figure 6 External memory extension circuit
Design of an Active Control System for Automotive Internal Noise
The control experimental system consists of four main parts: the model of automobile controlled system (with executor), external sound source, controller and signal monitoring (with sensor), as shown in Figure 7. One point to note is that in the control system, the controlled car model contains several aluminium plates, and only one of them is drawn here for ease of expression.
In the experimental system, external speakers are used to simulate the external excitation of the cabin. Sound waves emitted by speakers force a surface of an automobile model consisting of aluminium plates to vibrate, resulting in a loud noise inside the car. When the sound pressure sensor placed in the specified position inside the box detects the change of sound pressure there, it transmits the value of sound pressure to the DSP controller. The controller makes timely judgment according to the input and output of the system at this time and exerts control on the system. This control function is completed by the PZT executor pasted on the thin aluminium plate wall of the enclosed cabin, because the PZT can generate vibration energy under the control signal. Aluminum plates are also forced to vibrate to reduce noise at specified locations inside the car.
Figure 7 Diagram of experimental system composition
1 Automotive Controlled System Model
Because this design is developed for the internal noise of automobiles, a rough car model is used as the controlled object for the convenience of research. The model consists of 1mm aluminium plates on all sides, and a control sensor is installed on the body and inside the body. The executor of the control system is PZT, which is symmetrically mounted on the model.
Since piezoelectric ceramics have the ability to convert electrical energy into mechanical energy, the spontaneous dipole moment of the material changes when the application system is powered on to the piezoelectric ceramics, resulting in a change in the size of the material. This effect can produce 50% in 20ms μ M displacement, response speed is unparalleled by other materials, and the frequency band is very wide, temperature-insensitive, with the increase of the number of times of pressure, performance tends to be stable, and easy to integrate, is necessary for high-speed drivers. PZT piezoelectric material is selected as the actuator in this design.
2 External Source
In the experiment, the external sound source is replaced by the speaker, which is driven by the signal generator after the power amplifier.
3 Intelligent Controller
The intelligent controller based on the TMS320F2812 DSP chip can run independently offline and simulate online through the USB interface.
4 Signal Monitor
In order to monitor and process control error signals and piezoelectric drive signals in the box, the signal monitor of this control system uses a self-developed multi-function signal acquisition and processing system.
The piezoelectric material of the seat sensor selected in this design is the piezoelectric thin film PVDF. The signal sensed by PVDF is used as the reference signal of the system. PVDF is thin, soft, low density and highly sensitive, and has 10 times higher mechanical flexibility than piezoelectric ceramics. The piezoelectric properties of PVDF piezoelectric materials are 3-5 times higher than that of quartz, and the piezoelectric coefficients are higher, so they can be applied to the surface of objects.
conclusion
Based on TMS320F2812 DSP, this paper designs an intelligent controller which can run independently offline and simulate online through USB interface. An active intelligent control experimental system for automobile interior noise is designed with the controller. Through theoretical analysis, the control system has high data processing ability and processing speed, so it can play an important role in real-time control.
