Among many measuring instruments, the digital voltmeter should be a relatively advanced type of watch. When the voltage is measured by the staff, the measured value can be read intuitively through the liquid crystal display without the staff carefully checking the measurement grade. The measured value is converted and estimated, but during the observation and use, it can still be found that the worker cannot pay attention to the display phenomenon due to the need to pay attention to the measuring point during the measurement process. The voice voltmeter introduced in this paper can solve the above problem better. It can read the measured value in standard Chinese when the staff measures the voltage, which greatly facilitates the operation process of the staff.
Second, the design planThe block diagram of the voice voltmeter is shown in Figure 1.
(1) MCU
The microcontroller uses the AT8951, a low-voltage, high-performance CMOS 8-bit microprocessor with a 4K-byte flash programmable erasable read-only memory that is compatible with industry-standard MCS-51 instructions and output pins. Because the multifunction CPU and flash memory are combined in a single chip, the AT89C51 is a highly efficient microcontroller that is used in many embedded control systems.
(2) A/D conversion circuit
The A/D conversion circuit consists of two parts.
1. The range conversion circuit is a four-range digital voltmeter practical circuit composed of 7126 assembly. The four ranges are: 200mV, 2V, 20V, 200V. The voltage range is selected by the double-pole five-throw switch S1. When the S1 hits the range end, such as the 200V terminal, the digital voltmeter The measurement range is determined to be 0-200V.
2. The A/D circuit uses the ICL7126 chip as the core component of the A/D circuit. After the measured voltage is input, it is digital-analog converted and decoded by the internal circuit of ICL7126, and then sent to the liquid crystal display to display the voltage value of the measured voltage.
(3) Voice circuit
The voice circuit adopts ISD1420 chip. Its biggest feature is that it uses direct analog storage technology DAST to complete voice input, storage and segmentation, without having to go through A/D, D/ like other voice circuits. Complex digital information processing and transformation, such as A conversion, digital compression and speech synthesis, can better preserve the effective components in the analog to reduce distortion and improve the quality of recording and playback. It is easy to use, does not require a dedicated voice development system, is recorded and stored by a microphone; can be freely rewritten and deleted; there are a variety of information access methods for users to choose; flexible segmentation, strong anti-interference ability. When the 89S51 determines a certain number, the address code corresponding to the number is sent to the P1 port of the single chip, and an interrupt is generated, and the voice of the number is released.
It is based on AT89C51 single-chip microcomputer, consisting of ICL712631/2 digit digital voltmeter, voice circuit, power amplifier circuit, power supply and so on.
In the design, the characteristic speech signals of more than ten syllables such as “0, 1, 2, 10, 100, dot, volt, negative, and overrange†required by the voice voltmeter are first recorded through the voice circuit to generate more than ten segments of data. The speech block is used as the sound source for reading the voltage value. The input analog signal enters the single-chip microcomputer through the A/D conversion in the digital table, and is analyzed and judged by the single-chip microcomputer to find out the corresponding sound source in the speech block, and send it to the power amplifier circuit for amplification output, and read out the voltage value, thereby realizing intelligent measurement.
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