Scheme of non-contact infrared forehead thermometer

 scheme introduction: the non-contact infrared forehead 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 red external forehead thermometer is aligned and close to the effective distance detected by the digital proximity sensor, press the power / measurement key and keep it for several seconds, the infrared sensor module inside the infrared forehead thermometer will collect the temperature and convert it into an electrical signal, then convert the electrical signal into a digital signal, and then transmit it to the single chip microcomputer through the communication interface. The single chip microcomputer collects the current ambient temperature through the digital temperature sensor, carries out corresponding temperature compensation processing on the transmitted temperature digital signal, stores the corrected temperature as the current record number, and judges the LCD backlight range of the temperature, so as to carry out corresponding backlight display: (35.0-37.4 ℃) normal body temperature green backlight, (37.5-37.9 ℃) High body temperature yellow backlight, (38-42.9 ℃) high body temperature red backlight. If the body temperature is abnormal, it will also give a "didi didi" alarm, and finally broadcast the current temperature by voice. When it is not used for more than 30 seconds, it will automatically enter the low power consumption mode to save power.

 scheme hardware block diagram: this non-contact infrared forehead thermometer scheme is composed of ultra-low power consumption and high security MCU: rjm8l151, power module, key module, infrared sensor module, temperature sensor (module), digital proximity sensor module, ambient temperature sensor, voice module, speaker and LCD display module. Its hardware block diagram is as follows:

1. Microcontroller MCU

Rjm8l151 Series MCU with ultra-low power consumption and high security introduced by Wuhan ruinajie Electronic Technology Co., Ltd. The chip has excellent performance of operation and standby power consumption, supports 4-channel IO wake-up chip, and internally integrates 12 bit high-precision successive approximation ADC, 2-channel multifunctional comparator, timer, real-time clock (RTC), watchdog 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 and other modules, which are characterized by high cost performance, large storage capacity, high security, low power consumption and rich interfaces. The chip supports the development and debugging of application code using keiluvision or IAR integrated development environment. The hardware block diagram of rjm8l151 series safety MCU is shown in the figure below.

2. Power module

Two AAA dry batteries are used for power supply, and the voltage conversion chip is used to maintain the output voltage of the power module, so as to ensure the normal and stable operation of MCU, infrared sensor, digital proximity sensor, voice chip, LCD screen and other modules when the battery voltage drops.

3. Sensor module

3.1 the body temperature sensor module can select two different strategies:

A) The integrated infrared induction module is adopted, which includes infrared thermopile sensor and special processing chip. The advantages are stable circuit, simple interface and easy debugging, but the disadvantage is high price. MLX90614, HMS k1c1 f5.5 and 10tp583t can be selected as sensor signals. Examples are as follows:

The infrared sensing part of the infrared sensor MLX90614 is a 81101 thermoelectric unit. 81101 is an infrared thermopile sensor, which receives the infrared radiation signal of the target object, and then performs signal amplification and signal processing through the internal DSP signal processing special integrated chip mlx90302 and 17 bit ADC. It is output by PWM or SMBus (compatible with standard speed IIC). The measurement accuracy can reach 0.2%, Fast measurement speed, 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 make temperature compensation and improve the accuracy. The digital proximity sensor is used to detect the effective distance during temperature measurement

B) Using thermopile sensor + peripheral circuit has the advantage of low cost, but the disadvantage is that the small signal amplification and processing circuit and temperature compensation circuit need to be carefully designed and debugged, and the product design cycle is long. Sensor signals can be mtp10-b7f55, rtp678, etc. examples are as follows:

Mtp10-b7f55 of SUNIC can realize fast and high-precision temperature measurement. Its built-in NTC can realize ambient temperature measurement for temperature compensation to improve accuracy. Its application mode 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. The measurement can only be started under the condition of the best object distance ratio to ensure the accuracy of the measured data, such as tmd26721.

3.3 ambient temperature sensor

Its function is to obtain the ambient temperature during measurement, so as to eliminate the ambient temperature from the measured value of the infrared temperature sensor, obtain the measured human body temperature, and compensate the infrared temperature sensor. Some ambient temperature sensors are integrated into thermopile sensors, such as mtp10-b7f55.

4. The key module design includes five independent keys, namely power / measurement key, set key, up key, down key and mode key. The first four keys have sleep wake-up function.

Power / measurement key: press the key to sleep. After waking up, MCU performs a temperature measurement, and displays the current temperature after completion

Set key: after pressing the key to sleep and wake up, enter the function setting mode. Each press corresponds to the following functions in turn:

 F1 display unit switching: the default is ° C, press the up key to switch to ° F, and press the dowm key to switch to ° C

 F2 voice broadcast switch on / off: on by default, press the up key to switch to on, and press the dowm key to switch to off

 F3 delete temperature record

Up key: turn up from the current temperature record to temperature record 32, and turn it again to temperature record 1

Down key: scroll down from the current temperature record to temperature record 1, and then turn it again to temperature record 32

Mode key: human body / body surface mode switching

5. Voice module

The voice chip wtn1010 / vc505 is used to store voice segments, such as' ten points', 'Celsius',' Fahrenheit ',' one ',' two ',' nine ',' Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, Didi, did

6. LCD display module

Rfd-ta20001zt-11 is used to display the current temperature, current memory temperature, measurement mode, battery status, voice switch status and other information

 functional specifications of the scheme:

1) Measurement method: non-contact

2) Measuring distance: 3 ~ 8cm

3) Measurement mode:  human body mode: 32.0-42.9 ℃ (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 ℃ (35.0 ° - 42.0 ℃); ± 0.3C (other ranges)

6) Display resolution: 0.1 ° C or 0.1 ° f

7) Display units: ℃ (Celsius) and ° f (Fahrenheit)

8) Support 32 groups of storage memory

9) Support three color backlight display

 normal body temperature, green backlight (35.0-37.4 ℃)

 high body temperature, yellow backlight (37.5-37.9 ℃)

 ultra high temperature red backlight (38-42.9 ℃)

10) Support battery low voltage display

11) Support voice broadcasting

12) Support automatic shutdown and power saving

Advantages of rjm8l151:

1) Ultra low power consumption

Up to 6 low-power management modes can be selected, including deep sleep power consumption of 5na, external wake-up of less than 5us and support of 4-channel IO wake-up, low power consumption of 0.4ua in halt mode and RAM data retention, which can greatly prolong the service life of the battery.

2) Built in PVD programmable voltage detection

It can realize fast phased detection and management of the input voltage after battery boost.

3) Built in 12 bit high-precision successive approximation ADC

It can directly collect the real-time and accurate voltage of the battery, so as to digitally display and master the service state of the battery.

4) Rich communication interfaces

The chip supports uatr, SPI, IIC, GPIO, ISO7816, etc. for extended functions, peripheral devices can have more communication modes.

5) 15 bit watchdog timer

There is a built-in 15 bit watchdog timer, which can be used to reset the system when the system runs abnormally or crashes, return the system to normal operation, and further improve the stability of the system.

6) Memory security

High strength physical protection circuit is designed for internal flash, SRAM and other storage units to effectively prevent malicious code theft and reverse analysis.