Abstract: In view of the inconvenient reading of mercury thermometer, slow response speed and narrow surface in ordinary households, the design scheme of digital speech thermometer is proposed. The DS18B20 in stainless steel is used as the temperature sensor, the ISD1720 is used for voice recording and playback, and the STC89C52 single-chip microcomputer is used for temperature signal acquisition, data processing and voice playback control, and the actual circuit system is constructed. The experiment shows that the measurement range of the digital voice thermometer is 0~99. 9 °C, the display resolution is 0. 1 °C, the error is not more than 0. 5 °C, the temperature measurement speed is fast, the reading is convenient, the voice is clear, and the voice broadcast interval can be Tune, can be widely used in homes or occasions requiring temperature voice prompts.
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0 Preface
Temperature measurement plays an important role in people's daily life. When people feel uncomfortable, they usually need to measure body temperature. The baby in the house or the liquid food eaten by the patient, the bath water prepared for the baby, etc., need to sense the temperature in advance. If the temperature is too high or too low, it will cause harm to the patient or the baby. At present, the cheap thermometer is widely used at home, but it is usually only used to measure body temperature, the range is small, the maximum is 42 ° C; the reading is inconvenient, especially the elderly have poor eyesight, it is not easy to read accurately; inconvenient to measure outside the body temperature After use, and the mercury leakage after damage is harmful to the body, some countries have begun to ban the sale of mercury thermometers; non-contact infrared thermometers are convenient to use, but expensive. Literature [3] introduced a digital thermometer design method for industrial applications. The literature [4-5] introduced the method of designing a thermometer using a single-chip computer with voice processing function and a voice chip, but in the miniaturization and use of the instrument. Under the influence of convenience and cost, it is not easy to promote in general households, and its core technology is not disclosed. Therefore, it is of great practical value to develop a temperature measuring instrument which is convenient to use, can display digitally and has voice prompts, is inexpensive, and has a wide range of applications, and is particularly suitable for home use.
1 system design
1. 1 How the system works
The single-chip computer collects the signal of the temperature sensor, and the collected data is output to the digital tube for display after being processed, and is output to the voice module on the other hand, and the voice temperature prompt is performed, and the interval of the voice prompt is set by the dial switch. You can also turn off the voice function. The system block diagram is shown in Figure 1.
Figure 1 System block diagram
1. 2 system hardware design
1. 2. 1 temperature sensor
It adopts digital temperature sensor DS18B20, which adopts the networkable digital temperature sensor chip produced by American DALLAS Company. It is small in size, easy to use, and has various package forms. It is suitable for various small space digital temperature measurement and control fields. It can be measured due to project requirements. The liquid temperature is convenient for human body contact, etc. Therefore, the package form of the stainless steel protection tube is adopted, which has the functions of wear resistance, collision resistance and waterproof. DS18B20 can realize two-way communication only when it is connected to the microprocessor. It can measure temperature range: - 55~ + 125°C, programmable to 9~12 bit A/D conversion accuracy, temperature resolution is up to 0. 062 5°C. The measured temperature is serially output in a 16-bit digital way with symbol expansion; its operating power can be generated either at the far end or by parasitic power supply; multiple DS18B20s can be connected in parallel to 3 or 2 lines, CPU only A port line is required to communicate with many DS18B20s, which occupy fewer microprocessor ports and save a lot of leads and logic circuits. The connection circuit is shown in Figure 2:
Figure 2 Sensor connection diagram
In Figure 2, the 2 pin of the sensor is connected to the input/output (I/O) pin of the microcontroller, and the two sides communicate with each other. The pull-up is 4.7 kΩ. Since the DS18B20 single-line communication function is completed in a time-sharing manner, the system must strictly follow the protocol for its operations. The operation protocol is: Initialize DS18B20 (send reset pulse) → Send ROM function command → send memory operation command → process data, all operations have strict timing requirements.
1. 2. 2 single chip microcomputer
The MCC51-compatible STC89C52 has 8K bytes of in-system programmable Flash memory. Its MOSI, MISO, REST, SCK and other pins are latched and connected to the parallel port of the computer to program the internal Flash memory. With 512 B of RAM, 32 programmable I/O lines, and 3 16-bit timers/counters, it provides a highly flexible and ultra-efficient solution for many embedded control applications, making it ideal for this project. Applications.
1. 2. 3 voice module
Using the highly integrated and high-performance ISD1720 voice recording and playback chip produced by American Huabang Company, the sampling rate is adjusted between 4~12 kHz. According to the sampling frequency, 12~36 s voice information can be recorded. The voice information is in the voice information. The chip's internal solid-state multi-level memory array is stored in rows and can be precisely addressed by the 11-bit address in the instruction. The chipset integrates voice processing and storage, has repeated self-development, saves power information, and works independently. Button mode and SPI control mode, the recording and playback end automatically enters the low power state, can be directly * input or analog channel input, or the speaker can be directly output, the chip working voltage is between 2. 4~ 5. 5 V, can be multi-segment recording The basic storage unit entry address range is 0X010~0X09F. The application circuit is shown in Figure 3. According to the need, the recorded voice is divided into 13 segments, namely “zero to ten, point, degreeâ€, such as 37.5 degrees, and the broadcast is “three, ten, seven, five, five, degreesâ€, recording of each voice The time is about 1.35 s. Because the recording time is not easy to grasp accurately, the 13-segment voice is recorded by manual control, and then each voice recording effect is manually checked. As shown in Figure 3, the S4 is closed for voice information recording and loosening. At the end of the recording, the voice information is entered through the MIC, and the S5 key is triggered to play. The effect of the currently recorded information segment is checked. During the recording or playback process, the progress of the operation can be understood by flashing the LED; Not ideal, it must be deleted in time, because in the manual control mode, the delete operation is only valid for the beginning and last information; after the recording is completed, it must also check whether each piece of information is stored in the ring structure of the device in the storage system. This can be achieved by closing S5 and holding it. At this point, the device will play the current segment and its previous segment in sequence.
Figure 3 voice chip connection diagram
According to the range of voice storage addresses inside the chip, each segment of voice stores about 11 lines. In order to accurately know the entry address and end address of each voice, it can be checked by the single-chip microcomputer. The ISD1720 provides a 4-wire (SCLK, MOSI, MISO, SS) SPI interface to the microcontroller. Since the SPI timing of the two is not easy to coordinate, the system uses P1. 1, P1. 2, P1. 3, P1. 4 of the microcontroller. The ISD1720 is controlled by analog SPI timing. In the specific operation, after the device initialization is completed, the PLAY instruction is sent, and the device performs voice playback from the start address of the current information segment. When the end mark EOM of the segment of speech is encountered, the playback ends, and the positions of the recording pointer and the playback pointer are read ( That is, the status registers SR0 and SR1) are consulted, so that the start address and the end address of each voice can be accurately known. Since the system works normally, the SPI mode is adopted, and according to the measured temperature value, the corresponding voice segment entry is found, and the voice information is read out; in the SPI mode, the chip operation commands SET PLAY, S ET REC, SET? REASE has a first-in first-out buffer. Under the same type of SET command, a seamless connection can be made from one memory block to another, making it sound like the output temperature signal is continuous. of. In Figure 3, S1 is the reset button, S2 is the fast forward button, S3 is the delete button, S6 is the through mode selection button, S7 is for volume adjustment; the above switch buttons are all active low; R4 is the selection resistor for the voice sampling frequency When it is 80 k, the sampling frequency of voice recording is 8 kHz; when the voice announcement function is not used, the SW switch can be turned off, and the time interval of voice announcement is passed through a three-digit dialing code in the single-chip circuit. With the switch selection, 8 gear positions can be set, and the time parameters of each gear are controlled by the program.
1. 2. 4 display and power module
It adopts 3-digit LED digital display, retains one decimal, and the output mode adopts dynamic scanning mode. The two ports of the single-chip microcomputer are selected as the field line and word bit line of the LED after the driver, which reduces the total current of the output. For portable applications, the power supply adopts It is powered by a nine-volt battery and is stepped down to 5 V by the LM7805 for use by each module in the system. When wiring and making PCB boards, pay special attention to the processing of ground lines, requiring digital ground, analog ground, and ground of speakers to be individually routed, and finally connected to the power ground.
1. 3 system software design
The software flow of the system is shown in Figure 4.
Figure 4 system flow chart
After the system is initialized, the temperature sensor is reset, the temperature conversion is started, the temperature data is read, and the processing is performed. When the temperature is in a rapid change process, the system continuously collects and displays the temperature signal, and determines whether the interval of the voice broadcast arrives. When the requirements are met, according to the measured current temperature value, take out the values ​​of the ten, one and decimal places, and then check the corresponding voice signal entry address, reset the voice chip, send a power-on command and delay About 25 ms, to determine whether the power is normally turned on, after normal power-on, to clear the interrupt flag, to determine whether the device is ready to receive the next instruction, when ready, send the first paragraph of the playback command, and then check the status The register determines whether the device executes the instruction just sent normally. After normal execution, it determines whether the device is ready to receive the next instruction. Only when the device is ready, can the next instruction be sent to the device. Otherwise, the instruction may be caused. Lost. The program considers the FIFO buffer inside the device, so that the N-segment voice signal is played like a voice, and there is almost no dead time interval between each voice. When the voice broadcast is completed, the voice chip loses power, completes a voice broadcast, and the program returns to the beginning of the system to prepare for the next temperature acquisition, processing, display, and voice output process.
2 Conclusion
The digital voice thermometer designed by voice prompt and digital display has high precision and fast temperature measurement. It can be used for measuring body temperature as well as temperature of food, water and other materials. It has large measuring range and convenient operation. Not only suitable for ordinary families but also for some industrial field production applications that require voice prompts.
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