Designers and manufacturers hope that embedded controllers can provide new common functions for power monitoring and traffic management systems, including meeting requirements for electricity metering, vehicle monitoring, data collection, and sensor regulation. There are already many types and models of embedded controllers today, and the embedded controller based on mixed signals is a new and effective technology for realizing energy saving as a monitoring of these system functions.
Main technical specificationsToday, a new class of embedded controllers has emerged that can integrate high-performance data acquisition subsystems on the same silicon chip, with near DSP capabilities and RSIC-CPU cores, simplifying the external analog interface. Figure 1 illustrates the integration capabilities of modern embedded controllers (MAXQ series) and compares them with traditional microcontrollers.
The MAXQ family of embedded controllers represents this new generation of c. In addition to the usual UARTs (Universal Asynchronous Receivers, Transmitters), timers, and I/O ports, a set of simplified analog interface peripherals is also integrated:
One 16-bit, 8 million instructions per second (MIPS) and single-cycle RISC core;
2 UARTs with 32Kd flash memory, 512B RAM and independent baud rate generator
A pair of 16-bit Delta-Sigma() ADCs;
16-bit timer capable of operating in PWM mode
A 16 & TImes; 16 multiplier with a 40-bit accumulator.
The MAXQ family of embedded controllers also has a clock/calendar, an LCD controller, and hardware that simplifies the IR (infrared) communication channel interface. Includes three timers, one of which supports PWMD/A; infrared communication function; can drive 112-segment LCD controller; rely on battery backup, real-time clock with calendar and sub-second alarm clock function.
Application in power monitoring and traffic safety programMore and more appliances are always in power consumption. For example, in a refrigerator, the power supply includes an intermittent switch, and the power supply is turned on only when the internal temperature of the refrigerator is higher than a limited value. In fact, power-consuming devices are everywhere, and the multimedia device emits a light indicating that it is turned off and waiting for the command to be turned on again. In the past, closing the switch meant that the device no longer had any form of work. But today, turning off the TV just puts it in standby mode, and many circuits still consume power. In fact, it is difficult to find electrical appliances that actually cut off the power supply.
Microcomputers are also hidden power-consuming devices. In the age of the Internet, when people leave, they let the computer download files, receive e-mails, etc., and their power consumption is still worth studying.
MAXQ series embedded controller is an ideal choice in the power monitoring device design scheme. Figure 2 is a schematic block diagram of a specific design scheme.
application solution
The MAXQ series of embedded controllers have two ADCs designed to monitor the voltage and current channels. In this project, the MAXQ3120 continuously monitors the voltage and current entering a device. Then, it can report the average power of the device, the number and amplitude of power peaks, and the power factor of the device if needed.
The simplest and most straightforward reporting method is to configure a small LCD on the monitoring device. The LCD is inexpensive and can be very compact and easy to use when monitoring a single device. The embedded controller can switch between multiple display modes (voltage rms, current rms, power, degrees, etc.) and can be controlled using one or more buttons.
If you need to monitor multiple devices, you can set up a central station to record the data from each slave station. And less-than-ideal data transmission can be achieved with inexpensive modules. The embedded controller's ADC only has a sampling rate of 20,000 times per second. This rate cannot demodulate carriers in the 100kHz range (this band is commonly used in power line control systems), but they can demodulate the audio range. Carrier. If the data transfer rate is slow enough, such as about 10 bps, it can achieve very reliable communications. The master station can be a separate device or it can be connected to it through the serial port of the microcomputer. The latter solution is more attractive because the memory of the microcomputer is large enough and it can perform more complex tasks than the microcontroller.
Traffic safety in Doppler radar systems (see Figure 3).
In the early years, traffic management law enforcement agencies used Doppler speed radar, and the cost of such systems could be greatly reduced. Its use was not limited to dealing with speeding violators on road traffic. For example, the Pooler radar can alert the driver when the vehicle in front is parked.
System analysisAs we all know, the working principle of Doppler radar is relatively simple. The radar device transmits a continuous and known frequency microbeam, which is reflected when the microbeam encounters a moving target. Since the frequency of the reflected wave is slightly higher or lower than the frequency of the transmitted wave, a frequency (called “beat toneâ€) can be obtained by mixing the reflected wave and the transmitted wave. The formula is as follows:
V=[v&TImes;(f0/c)]&TImes;COS
Among them, v is the speed of the target to be measured, f0 is the rated transmission frequency, which is the angle between the target movement direction and the radar system (as shown in Figure 4), c is the speed of light. It is worth mentioning that if the target comes directly to the radar system, then =0, COS=1, the target's movement speed becomes:
If the Ku-band Doppler radar produces a "beat tone" with a frequency of 1 kHz, the measured target comes straight (or away) at a speed of 12.4 m/s (ie 28 miles or 45 kilometers per hour). The embedded controller can be used to process this audio signal.
Utilizing one of the two ADC channels, the embedded controller can sample the differential signal output by the radar module, extract the strongest frequency component of it, and convert it to kilometers per hour or miles. In addition, the use of its multiplication-adding unit can also perform some complex filtering operations to extract the strongest frequency components from the complex signals and may extract useful information from weak signals (eg, Doppler radar system The speed of the vehicle itself).
In many cases, the design of the user interface is very trivial, often with some logic processing or triggering an audio alert via a switch. In some applications, the microcontroller also needs to record the speed periodically, as well as the time and date of the speed measurement.
Doppler radar system applicationsFor more complex measurement and analysis systems, it is also necessary to develop algorithms for signal processing. The MAXQ embedded controller has many ready-made tools that can be used to assist in the development of filtering algorithms and recognition algorithms.
If some radar systems need to indicate the direction of motion of the target, it is measured whether the target is moving away from or near the radar. Traditional Doppler radars cannot do this because they produce the same amount of frequency shift for the same speed and opposite direction of motion.
Now some manufacturers produce radar modules that contain two orthogonal outputs and demodulate the two outputs. According to their phase differences, the radar system can determine the direction of the target's motion. The MAXQ3120 has two ADCs that make it easy to implement this function.
Voice Record Monitoring SystemDesign idea
Typically, a microcontroller and an analog-to-digital converter (ADC) are used to record voice. However, in addition to simple sound recording, the MAXQ3 embedded controller can also do a lot of things. That is, with the controller as the core, with user interface components and inexpensive NAND flash memory, a full-featured voice recording monitoring system can be built. Can become the power system monitoring and traffic safety voice recording subsystem.
Because the embedded controller is an ideal microcontroller for advanced speech recording systems. When using it to design a voice recording monitoring system, the designer only needs to complete the following tasks:
Design user interface: Select an LCD to determine how to display information, set button functions, how to record and organize voice data;
Select vocoder: one of the two ITU encoders can be selected, or other dedicated encoders can be used. When the memory capacity is large enough, the original sampled value of the voice signal can also be directly stored. The C language source code of many standard encoders is available, so simply develop the interface program;
Select storage media: NAND flash memory is the ideal choice, but also can choose other memory according to the actual situation, for example, cheap universal removable memory (SD, SmartMedia or MMC memory card). Some vendors also provide C language source code and development tools for memory card interfaces.
Battery Management: If you use a battery, you need some form of power management. There are many efficient low-power battery management solutions available today. Combining these solutions with the low-power stop and sleep modes of the embedded controller will give the voice recorder a satisfactory battery life.
Program compositionImplement audio I/O with an ADC and PWM timer on the MAXQ series embedded controllers. The ADC's rated input voltage is +1V to -1V, and its built-in preamplifier has a programmable gain of 16X. In general, capacitive pickups with built-in impedance matching can be connected directly to the input of the ADC. If low noise or high gain is required, a preamplifier, the MAX4467, can be used, which provides the necessary bias for the pickup and provides a very low power shutdown mode for battery-powered applications. At the output, a single-stage amplifier is used to drive the speaker, which also has some anti-aliasing and PWM smoothing capabilities.
Process analysisAfter the audio signal is converted into a digital signal, it must be compressed and stored for playback. The processing power of 8 MIPS (8 million instructions per second) enables the embedded controller to have enough "horsepower" to cope with many common standard speech coding tasks. The "golden rule" in this field is the ITUG.711 encoding, which operates at 64 kbps and sends and receives 8000 8-bit samples per second. This encoding has two different transfer functions that are used to convert 12-bit samples into 8-bit encoded words.
During the recording phase, the timer generates an interrupt request every 125 seconds (every 1000 processor cycles at 8MHz clock frequency). After the microprocessor responds to an interrupt, it calculates the average of the sampled values ​​obtained during the previous timer period (two or three samples, and the ADC samples every 48 s) in order to obtain the required 8 kHz sample rate. After that, the collected 16-bit samples can be encoded using the selected encoding scheme. During the playback, the sampled data is linearized and sent to the PWM controller to drive the speaker.
The compressed audio data can be used for storage, but the embedded controller has no memory other than the program flash memory, so it needs to use external memory to store voice data. The most cost-effective external memory for this application is NAND flash, which has a capacity of up to 8G bits. For 16kbps encoding, this device can provide more than 6 days of voice storage. But NAND flash is not perfect. First of all, most NAND flash devices come with a “map†that tells the application where there is a “bad spot†in the memory array. Second, like other erasable memories, some units of NAND flash memory lose their storage capacity after long-term use. Fortunately, these defects in NAND flash have little impact on voice applications, unlike the impact on applications such as solid state disks. In speech applications, these NAND flash memory defects can be ignored. They can cause transient noises in the speech.
For voice storage of such a large capacity, effective storage management must be performed by the user interface part of the system. The core of the user interface part is the LCD controller, which can drive 28 segments of display on 4 common surfaces. The MAXQ series embedded controller's LCD controller is compatible with a large number of existing 3V LCD glass. Custom LCD modules can be obtained at a very low cost.
The user can control the voice monitoring and recording system through the button connected to the universal I/O port. The MAXQ series of embedded controllers have four 8-bit general-purpose I/O ports that are multiplexed with other device functions.
ConclusionThe clever use of the embedded controller can be used as a core for multi-function meter monitoring and application in traffic safety management and voice recording subsystems. The powerful features make this MAXQ series embedded controller have the opportunity to expand in many application areas, it is very likely that the next one is the application program of the mixed-signal application project.
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