Solution introduction: Non-contact infrared thermometer is a new instrument that uses modern sensor measurement technology, microelectronic technology and other technical means to measure the temperature of the measured object. When the infrared thermometer is aligned and close to the measured object to the effective distance detected by the digital proximity sensor, press the power/measurement key and hold it for a few seconds, then the infrared sensor module inside the infrared thermometer will collect the temperature , And converted into electrical signals, followed by the conversion of electrical signals into digital signals, and then transmitted to the microcontroller through the communication interface. The MCU collects the current ambient temperature through a digital temperature sensor, performs corresponding temperature compensation processing on the transmitted temperature digital signal, and stores the corrected temperature as the current record number, and at the same time determines the LCD backlight range where the temperature is located, so as to perform the corresponding backlight display : (35.0-37.4℃) normal backlight with green body temperature, (37.5-37.9℃) yellow backlight with high body temperature, (38-42.9℃) red backlight with super high body temperature, if the body temperature is abnormal, "dididididididididi" will also be carried out Alarm, and finally voice broadcast the current temperature. When not used for more than 30 seconds, it automatically enters a low-power mode to save power.
Solution hardware block diagram: This non-contact infrared forehead thermometer solution consists of ultra-low power consumption and high security MCU: RJM8L151, power supply module, key module, infrared sensor module, temperature sensor (module), digital proximity sensor module, Ambient temperature sensor, voice module, speaker and LCD display module, the hardware block diagram is as follows:
1. Microcontroller MCU
It adopts the ultra-low power consumption and high security RJM8L151 series MCUs launched by Wuhan Renajet Electronic Technology Co., Ltd. The chip has excellent running and standby power consumption performance, supports 4-way IO wake-up chip, internally integrated 12-bit high-precision successive approximation ADC, 2-channel multi-function comparator, timer, real-time clock (RTC), watchdog Dog timer (WDT), power programmable voltage detection (PVD), interrupt controller, hardware true random number generator, AES/DES/SM4 hardware encryption engine and communication interface: UATR, SPI, IIC, GPIO, ISO7816, JTAG Such modules have the characteristics of high cost performance, large storage capacity, high security, low power consumption and rich interfaces. The chip supports KeiluVision or IAR integrated development environment to develop and debug application code. The hardware block diagram of RJM8L151 series safety MCU is shown in the figure below.
2. Power module
It is powered by 2 AAA dry batteries, and the voltage conversion chip is used to maintain the output voltage of the power module to ensure that the MCU, infrared sensor, digital proximity sensor, voice chip, LCD screen and other modules work normally and stably when the battery voltage drops.
3. Sensor module
3.1 The body temperature sensor module can choose two different strategies:
A) The integrated infrared sensor module is used. The module includes an infrared thermopile sensor and a special processing chip. The advantage is that the circuit is stable, the interface is simple, and the debugging is easy. The disadvantage is that the price is higher. The sensor signals can be MLX90614, HMS K1C1 F5.5 and 10TP583T, etc. The examples are as follows:
The infrared sensor part of the infrared sensor MLX90614 is the 81101 thermoelectric unit, 81101 is the infrared thermopile sensor, which receives the infrared radiation signal of the target object, and then uses the internal DSP signal processing special integrated chip MLX90302 and 17-bit ADC for signal amplification, signal processing, etc. Process, output by PWM or SMBus (compatible with standard speed IIC) measurement accuracy can reach 0.2%, measurement speed is fast, low power consumption MLX90614 supports sleep mode. The digital temperature sensor is mainly used to measure the ambient temperature, so that the infrared sensor can be used as a temperature compensation to improve the accuracy, and the digital proximity sensor is used to detect the effective distance during temperature measurement
B) The use of thermopile sensors + peripheral circuits has the advantage of lower cost, but the disadvantage is that small signal amplification and processing circuits and temperature compensation circuits require careful design and debugging, and the product design cycle is longer. The sensor signal can be MTP10-B7F55, RTP678, etc. The examples are as follows:
Using Sonich's MTP10-B7F55, it can achieve fast and high-precision temperature measurement, its built-in NTC can realize ambient temperature measurement to perform temperature compensation to improve accuracy, and its application method can be flexibly selected. The principle is as follows:
(A) Software temperature compensation (b) Hardware temperature compensation
(C) Analog interface (d) Digital interface
3.2 Digital proximity sensor
It is used to judge the distance between the measured object and the PIR sensor. Only when the object distance ratio is the best, the measurement is started to ensure the accuracy of the measurement data, such as TMD26721.
3.3 Ambient temperature sensor
Its function is to obtain the ambient temperature at the time of measurement, so as to remove the ambient temperature from the measured value of the infrared temperature sensor, obtain the temperature of the human body to be measured, and compensate the infrared temperature sensor. Some ambient temperature sensors are integrated into thermopile sensors, such as MTP10-B7F55.
4. The button module design includes 5 independent buttons, namely the power/measurement button, SET button, UP button, DOWN button, and MODE button, among which the first 4 buttons have a sleep wake-up function.
Power/measurement key: press the button to sleep and wake up the MCU to perform a temperature measurement and display the current temperature after completion
SET button: After pressing the button to sleep and wake up, enter the function setting mode, each press corresponds to the following functions in turn:
F1 display unit switch: the default is °C, press the UP key to switch to °F, press the DOWM key to switch to °C
F2 Voice broadcast switch ON/OFF: the default is ON, press the UP button to switch to ON, press the DOWM button to switch to OFF
F3 delete temperature record
UP key: turn up from the current temperature record until the temperature record is 32, and turn to the temperature record 1 again
DOWN key: Scroll down from the current temperature record until temperature record 1, and turn to temperature record 32 again
MODE key: body/body surface mode switch
5. Voice module
Use voice chip WTN1010/VC505 to store voice clips, such as'ten o'clock','℃','℉','one','two', ,,'nine','didididididididi', etc., through Select the segment to play and join together to form a complete voice, drive the speaker to sound
6. LCD display module
Use RFD-TA20001ZT-11 to display the current temperature, current memory temperature, measurement mode, battery status, voice switch status and other information
Scheme functional specifications:
1) Measurement method: non-contact
2) Measuring distance: 3~8CM
3) Measurement mode: Human body model: 32.0-42.9°C (89.6-109.3°F)
Body surface mode: 0.0-99.9℃(32.0-211.9°F)
4) Measurement time: <6s
5) Measurement accuracy: ±0.2°C (35.0°-42.0°C); ±0.3C (other ranges)
6) Display resolution: 0.1°C or 0.1°F
7) Display unit: ℃ (Celsius) and °F (Fahrenheit)
8) Support 32 groups of storage memory
9) Support three-color backlight display
Green backlight with normal body temperature (35.0-37.4℃)
High body temperature yellow backlight (37.5-37.9℃)
Super high temperature red backlight (38-42.9℃)
10) Support battery low voltage display
11) Support voice broadcast
12) Support automatic shutdown to save power
Advantages of RJM8L151:
1) Ultra-low power consumption
Up to 6 low-power management modes are available, including deep sleep power consumption of 5nA, external wake-up less than 5us and support 4-way IO wake-up, power consumption as low as 0.4uA in Halt mode and RAM data retention, etc. Service life.
2) Built-in PVD programmable voltage detection
The input voltage after the battery is boosted can be quickly detected and managed in stages.
3) Built-in 12-bit high-precision successive approximation ADC
Can carry on real-time, accurate voltage collection to the battery directly in order to digitally display and grasp the use state of the battery.
4) Rich communication interface
The chip supports UATR, SPI, IIC, GPIO, ISO7816, etc. For extended functions, peripheral devices can have more choices of communication methods.
5) 15-bit watchdog timer
There is a 15-bit watchdog timer built-in, which can be used to reset the system when the system is running abnormally or crashes, returning the system to normal operation, which further improves the stability of the system.
6) Memory security
High-strength physical protection circuits are designed for internal Flash, SRAM and other storage units to effectively prevent malicious code theft and reverse analysis.