Technical principle of frontal temperature gun

Technical principle of frontal temperature gun

1.       Appearance

A complete foreheadtemperature gun product is composed of three parts: shell, internal circuit board and battery (system power supply). We will not mention the shell, which belongs to the design category of structural engineers. The following focuses on the internal circuit composition.

From the structure diagram of the frontal temperature gun above, it can be seen that the circuit components are: LED display, infrared temperature sensor, battery, buttons, buzzer, etc.

2.       Block diagram of hardware structure

According to the above composition, we can draw a block diagram of the approximate hardware structure of the front temperature gun.

• Infrared temperature sensor: It is used to collect the temperature of the human body / object. The infrared forehead temperature gun is generally measured at a distance of 1 ~ 3cm from the forehead. The collected data is amplified by a signal amplification circuit. The signal amplification circuit is optional.
• MCU microprocessor: accept infrared temperature sensor data for processing, for analog sensors, need to add A / D conversion circuit to convert analog signals into digital signals, and then to MCU processing; for digital temperature sensors, you can Process directly to the MCU.
• Button module: used for mode switching, measuring objects, measuring forehead, measuring neck and other modes. The buttons can be customized, and can be used as a power-on button and a system reset button.
• LCD display: MCU control, used to display temperature data.
• Buzzer: Alarm module. The MCU sets a normal temperature range, such as 35 ~ 37.3 ℃. If it exceeds the upper limit or lower than the lower limit, the buzzer will alarm and the temperature is too low or too high.
• Crystal oscillator circuit: a clock used for MCU microprocessing to provide a source of oscillation.
• Battery: The battery is the main power source of the entire system. Because of the portability of the front temperature gun, it must be battery-powered. The most important thing is battery-powered products. The most important thing is low power consumption. When not working, the system needs to enter sleep mode to achieve Lower power consumption and extended battery life.
• Power management: The power supply voltage of modules such as infrared temperature sensor, display screen, buzzer, etc. is not necessarily the same. The battery needs to be converted to a suitable voltage value to supply power to each module. Of course, a rechargeable battery can also be used to add a charging circuit.

3.       Infrared temperature sensor

The front temperature gun is actually a single-chip processing system. The most important thing is the infrared temperature sensor module. The sensor also determines the accuracy of the measurement. The following introduces a commonly used infrared temperature sensor MLX90615. The MLX90615 is a digital sensor. No additional A is needed during development. / D conversion circuit, the highest precision can reach 0.2 ℃, because of its small size and convenient development, it is still used more now.

The small size reduces the space occupied by internal circuits and makes the product more portable

Operating voltage 3V, lower voltage means lower power consumption, power-down mode current is only 1.1uA, which means that the battery power consumption when the thermometer is not working is very small, this parameter is very important for battery-powered products .

Internal block diagram

Pin definition, support PWM and SMBus two modes

Summary

Any object above the absolute zero (-273 ℃) will emit infrared rays. The forehead gun receives infrared rays through the infrared temperature sensor to calculate the temperature data. The realization of the forehead gun is actually not difficult. Friends should be able to make their own implementation.