Design scheme of infrared forehead thermometer Industry News Silver Wing

Introduction

Non-contact infrared forehead thermometer is a new type of instrument that uses modern sensor measurement technology, microelectronic technology and other technical means to measure the temperature of the measured object. When the infrared forehead thermometer is aligned and close to the measured object to the effective distance detected by the digital proximity sensor, press the power/measure button and hold it for several seconds, then the infrared sensor module inside the infrared forehead thermometer will collect temperature , And converted into electrical signals, then the electrical signals are converted into digital signals, and then transmitted to the microcontroller through the communication interface. The single-chip microcomputer collects the current ambient temperature through the digital temperature sensor to perform 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 body temperature with green backlight, (37.5-37.9℃) high body temperature with yellow backlight, (38-42.9℃) high body temperature with red backlight, if the body temperature is abnormal, it will also perform "di di di di di" Alarm, and finally voice broadcast the current temperature. When it is not used for more than 30 seconds, it will automatically enter the low power mode to save power.

Scheme hardware frame

This non-contact infrared forehead thermometer solution consists of ultra-low power consumption, high-security MCU: RJM8L151, power module, button module, infrared sensor module, temperature sensor (module), digital proximity sensor module, ambient temperature sensor, voice It consists of module, speaker and LCD display module, and its hardware block diagram is as follows:

Infrared Forehead Thermometer

1. Microcontroller MCU

It adopts the ultra-low power consumption and high-security RJM8L151 series MCU launched by Wuhan Renajie Electronic Technology Co., Ltd. The chip has excellent performance in operation and standby power consumption, supports 4-channel IO wake-up chip, internally integrates 12-bit high-precision successive approximation ADC, 2-channel multi-function comparator, timer, real-time clock (RTC), gatekeeper 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:

Infrared Forehead Thermometer

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

A) The integrated infrared sensor module is adopted. The module includes an infrared thermopile sensor and a special processing chip. The advantages are stable circuit, simple interface and easy debugging, but the disadvantage is higher price. The sensor signal can choose MLX90614, HMS K1C1 F5.5 and 10TP583T, etc. The examples are as follows:

The infrared sensing part of the infrared sensor MLX90614 is the 81101 thermoelectric unit, and the 81101 is the infrared thermopile sensor, which receives the infrared radiation signal of the target object, and then uses the internal DSP signal processing dedicated integrated chip MLX90302 and 17-bit ADC for signal amplification and signal processing. During the process, output by PWM or SMBus mode (compatible with standard speed IIC), the measurement accuracy can reach 0.2%, the measurement speed is fast, and the 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 for 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 sensor + peripheral circuit has the advantage of lower 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 longer. The sensor signal can be MTP10-B7F55, RTP678, etc. The examples are as follows:

Using Sonnich’s MTP10-B7F55, it can achieve fast and high-precision temperature measurement. Its built-in NTC can achieve ambient temperature measurement for temperature compensation to improve accuracy. Its application method can be flexibly selected. The principle is as follows:

(A) Software temperature compensation (b) Hardware temperature compensation

Infrared Forehead Thermometer

3.2 Digital proximity sensor

It is used to judge the distance between the measured object and the PIR sensor. The measurement is started only when the object distance ratio is the best 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 exclude the ambient temperature from the measured value of the infrared temperature sensor, obtain the temperature of the measured human body, and compensate the infrared temperature sensor. Some ambient temperature sensors are integrated into thermopile sensors, such as MTP10-B7F55.

4. Button module

The design includes 5 independent buttons, namely the power/measurement button, the SET button, the UP button, the DOWN button, and the MODE button. The first 4 buttons have a sleep wake-up function.

Power/Measuring button: Press the button to wake up after sleep and the MCU will perform a temperature measurement, and display the current temperature after completion

SET button: Press the button to wake up from sleep and 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 key to switch to ON, press the DOWM key to switch to OFF

F3 delete temperature record

UP key: scroll up from the current temperature record until the temperature record 32, then turn to temperature record 1 again

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

MODE key: Human body/body surface mode switch

5. Voice module

The voice chip WTN1010/VC505 is used to store voice fragments, such as'ten o'clock','℃','℉','one','two',,,'nine','dididi', etc., through Play the excerpts and put them together to form a complete voice, driving the speaker to sound

6.LCD display module

Use RFD-TA20001ZT-11 to display current temperature, current memory temperature, measurement mode, battery status, voice switch status and other information

Solution function specifications

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°C (32.0-211.9°F)

4) Measuring 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

Normal body temperature with green backlight (35.0-37.4℃)

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

Super high body 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-channel IO wake-up, Halt mode power consumption as low as 0.4uA and RAM data retention, etc., which can greatly extend the battery Life.

2) Built-in PVD programmable voltage detection

It can realize rapid phase detection and management of the input voltage after the battery is boosted.

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

It can directly collect the real-time and accurate voltage of the battery in order to digitally display and grasp the battery status.

4) Rich communication interface

The chip supports UATR, SPI, IIC, GPIO, ISO7816, etc. For extended functions, peripheral devices can have more communication options.

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, and returns 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.

Digital circuit technology of ear thermometer

The principle of digital processing method is to convert the thermistor and thermopile signals into electrical signals and amplify them. Through A/D conversion, the data collected by the single-chip microcomputer can be calculated and processed internally to obtain the corresponding temperature value.
Infrared Forehead Thermometer

website：http://www.silverwing.com.hk/news_view_2043_153.html

Company

Industry

Product Update..

Product Inform..

AE

Amotech

Central

Harvatek

Pocons

JoYin

Damai

iA

ECS

ITW

SANICO

Sangshin

EVE

Carling

RN2

ABCO

C² Battery

Amphenol

Contact us

Design scheme of infrared forehead thermometer

Related News