Design of intelligent thermometer based on single chip microcomputer SPCE061A

O Introduction

Commonly used thermometers can be divided into the following types according to their materials and uses: glass mercury thermometers, which are accurate and inexpensive, but must be in direct contact with the human body for more than 3 minutes, and are difficult to read due to their fine scales, and also have disadvantages such as being fragile; electronic digital display thermometers, which display body temperature in digital form, have improved on the disadvantage of glass mercury thermometers being difficult to read, but still have the disadvantage of requiring constant attention to the thermometer in an emergency; sticker thermometers, which are easy to use but not very accurate; pacifier thermometers, which are special thermometers and inconvenient to use at night; ear thermometers, which are expensive; disposable thermometers are relatively expensive, etc.

Based on the digital thermometer, digital voice technology is used. The measurement results are broadcasted by voice, which can give full play to the advantages of hearing, make up for the shortcomings of completely transmitting information with optical signals, realize the transition of temperature measurement from "query mode" to "interruption mode", and give full play to the advantages of interruption mode, such as in dimly lit places or when the eyes are paying attention to other details or other special situations (such as long-term temperature monitoring at night). This paper designs and develops a new type of intelligent thermometer that integrates programmable (setting parameters), voice broadcast, over-limit alarm functions, and can display temperature change curves online and can be used online. It can be widely used in the medical and health industry and even at home, such as nighttime body temperature measurement and temperature monitoring. When monitoring critically ill patients, setting a suitable alarm temperature value can effectively reduce the workload of monitoring personnel, and at the same time, abnormal temperature can be discovered in time. Through networking operation, it can also play its advantages in the detection of highly infectious diseases related to body temperature, and can effectively protect medical personnel. The thermometer is programmable and can be cut down by itself, which brings great flexibility to the use of the thermometer and can be promoted and used in different industries that require temperature measurement.

1 System Design Goals

(1) The system uses voice to report the real-time value of the measured temperature once every minute, without false alarms or missed alarms. When the measured temperature exceeds the warning temperature value, the system will immediately alarm.

(2) The system warning temperature value can be set arbitrarily within the range of -55.0 to +125.0°C (the default value is set to 37.0°C).

(3) Record temperature measurement results and connect to a computer to display the temperature change curve.

(4) The measurement accuracy is ±0.1℃ (or 0.2F).

(5) The system has a simple structure, is easy to use and reasonably priced.

2 Hardware Design

The system adopts the mature solution of general automatic test system, which is composed of main control microcontroller, temperature measurement circuit, voice broadcast and programming circuit.

2.1 Selection of main control chip

There are many main control chips to choose from, such as the most widely used MCS-5l series, the resource-rich ARM7TDMI-S series microcontrollers, the low-power MSP430 series, etc. Considering the cost-effective implementation of voice broadcast and voice programming functions, the 16-bit μ'nSPTM core microcontroller SPCE061A launched by Taiwan Lingyang Company is used. Its high processing speed can easily and quickly process complex digital signals, and it is also the most economical choice for products in the field of digital voice recognition applications.

2.2 Temperature measurement scheme

There are many mature temperature measurement solutions in different temperature measurement ranges, such as temperature measurement systems using thermistors, platinum resistors, and integrated temperature sensors. The current popular digital temperature sensors are AD7416, MAX6575L/H, and DS18X20. The former two are mostly used for temperature detection inside computers or instruments and equipment. In view of the simple interface of the latter, and its good performance in terms of measurement accuracy, device reliability, stability, and parameter consistency, it is widely used. Because its temperature measurement error does not exceed ±0.5℃ in the range of -10～+85℃, and it has a 12-bit resolution, it is very popular in various applicable fields. This system uses DS18B20, which has its own signal conditioning and A/D conversion. The hardware interface between the sensor and the single-chip microcomputer is very simple. It only needs to be connected to the single-chip microcomputer through a data line, so the high reliability of the system is guaranteed. In order to achieve a measurement accuracy of ±0.1°C, the "remaining pulse number" and "pulse number per degree" in SCRATCHPAD of DS18B20 are used. The measurement accuracy of ±0.1°C can be obtained through the formula: high-resolution temperature value = TI-0.25 + (Tp-TR)/TP.

2.3 Voice broadcast

For voice broadcast, the common practice is to use a single-chip microcomputer to operate ISDl420 to achieve it, which uses more hardware and wiring, so the reliability and cost of the system are not advantageous. This design uses the SPCE061A single-chip microcomputer. Due to its powerful signal processing function, the single-chip microcomputer can directly output voice signals without the need for other voice chips, thereby greatly improving the reliability of the system.

2.4 Voice Control (Programming)

There are also ready-made chips for voice control. Since the single-chip microcomputer used in this system has strong digital signal processing capabilities, and its Mic input has an integrated AGC circuit, making voice control more stable, SPCE061A is used directly to implement voice control. Since the voice recognition API provided by Lingyang is based on specific person voice recognition technology, users need to train the system before use. At the same time, the voice recognition rate is high only for trained people, so it is very inconvenient to use. This system is based on the recognition algorithm of the DHMM model, uses the BaumWelch method to train the template, and the Viterbi algorithm to recognize non-specific person voice recognition, so that users can directly control without tedious training, and different users do not need to be trained repeatedly, which greatly enhances the adaptability of the system.

2.5 Keyboard Circuit

Considering the speaking habits of users, for some users, it is not convenient to use voice control, so a keyboard circuit is set to solve the setting (programming) problem, so the keyboard circuit is required to be very simple and has little impact on the overall cost. SPCE06IA has two 16-bit general I/O interfaces Port A and Port B, and Port A has a wake-up function, so the A port direct control keyboard is used.

2.6 Networking Function

SPCE061A also provides a universal asynchronous serial interface UART, so it can be directly used to connect to the Internet to achieve isolation between the temperature measurement personnel and the measured object, that is, long-distance and multi-point temperature measurement.

In summary, the overall hardware circuit composition is shown in Figure 1. The SCPE061A single-chip microcomputer realizes the overall control of the system and implements voice or keyboard programming and voice broadcasting. The system can realize networking function through the universal asynchronous serial interface. In situations where networking is not required, the thermometer can also be used alone, realizing the system's tailorability. DSl8B20 is used to realize temperature detection.

3 Software Design

The main task of software design is to broadcast the measured temperature through voice and receive programming data to make the system work in different states.

3.1 Temperature detection

When measuring temperature through DS18B20, the controller is required to communicate strictly in accordance with its single bus protocol. There have been many discussions about the communication control program of DS18B20, which will not be repeated here.

3.2 Voice broadcast

The API provided by Lingyang Company can directly play compressed voice, so the digital signal (file) of ten numbers from 0 to 9 and voice such as degrees Celsius, setting, and alarm temperature can be compressed and directly written into the microcontroller. When broadcasting the temperature, the temperature parameters can be passed to the playback program to realize the voice broadcast or alarm function.

3.3 Parameter settings

Parameter settings can be achieved through voice control and keyboard input. For users who are good at Mandarin, they can directly use voice control to adjust system parameters, while users who are not so good at Mandarin (low recognition rate) can choose to use the keyboard to adjust system parameters. The system uses non-specific person speech recognition technology, making the use of language control system relatively simple and convenient. At the same time, the keyboard design also provides another option for people who are not convenient to use voice control, which can adapt to different types of users.

The parameters that can be set mainly include the broadcast mode: "continuous, every x seconds, prohibited"; alarm temperature value; working mode, etc. When you need to pay attention to the temperature value in real time, you can set it to continuous broadcast; when the temperature changes slowly, you can set it to every x seconds; after setting the alarm mode at night, you can set it to prohibit broadcast mode. After setting the alarm temperature value, you can handle other things. When an alarm occurs, the system will give an alarm to prompt the user. After selecting the working mode as "network work", in addition to on-site broadcasts and alarms, the system will also send the corresponding information to the remote end through the asynchronous serial port. The setting process is all done in voice menu mode, which can greatly reduce costs. The setting flow chart is shown in Figure 2.

4 Conclusion

The intelligent thermometer designed in this paper has a simple circuit, few components, high measurement accuracy, strong anti-interference ability, and can realize functions such as real-time temperature measurement, over-limit alarm, and voice broadcast. Since various functions are realized by a single-chip microcomputer, different temperature measurement modes can be added according to specific requirements, achieving the design goal, and can be widely used in temperature measurement and cost-effective fields, especially special applications.