How to quickly design an infrared body temperature detector? TI is here to help!

“Body temperature detection is a necessary monitoring for us at home, in and out of the community or workplace, and when we travel. Infrared temperature detectors help reduce contact infection through non-contact temperature measurement. Here we come to talk to you about this system and the main design scheme.

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Body temperature detection is a necessary monitoring for us at home, in and out of the community or workplace, and when we travel. Infrared temperature detectors help reduce contact infection through non-contact temperature measurement. Here we come to talk to you about this system and the main design scheme.

The MSP430 series microcontroller is a 16-bit ultra-low power consumption RISC mixed-signal processor introduced to the market by Texas Instruments (TI) in 1996. There are countless applications developed based on this series of products, especially for sensing And detection terminal applications, because of the high-performance ADC, LCD driver, serial communication, PWM output and other modules integrated on the chip, it has become the best choice for infrared body temperature detector manufacturers. With the rich online software and hardware design resources provided by TI, developers can greatly simplify the design process, quickly develop prototypes of infrared body temperature detectors, and save circuit board space to reduce costs.

The figure below provides an infrared temperature detector system solution based on MSP430 microcontroller and TI power management, amplifier and temperature sensor devices.

Figure 1 System block diagram of infrared body temperature detector

As the main control MCU of the solution, MSP430 series single-chip microcomputer can provide the following functions and features for the design of the thermometer system:

Rich peripherals meet the design requirements of thermometers:

1. The successive approximation SAR ADC or high-resolution Sigma-Delta ADC integrated on the MSP430 chip cooperates with TI’s TLV333 amplifier to sample the high-precision signal quantity collected by the analog infrared temperature sensor and convert the digital temperature quantity, and can also measure the battery voltage. conduct real-time monitoring;

2. The LCD driver module integrated on the MSP430 chip can help developers to quickly realize the design of LCD Display for the thermometer. The built-in LCD driver module of MSP430FR4133 up to 4×36 segments or 8×32 segments supports flexible configuration of LCD Segment and COM pins, which can simplify the developer’s PCB design;

3. The I2C serial communication interface can meet the signal acquisition and input of high-precision digital temperature sensor or digital infrared temperature sensor, digital proximity sensor and other auxiliary sensing elements;

4. The timer module integrated on the chip can output multiple PWM signals to drive the thermometer indicator light, buzzer and other devices;

5. GPIO interrupt enable in ultra-low power mode can provide fast button response in standby mode for battery-powered thermometer system.

The ultra-low power consumption design helps the thermometer’s long battery life and high frequency of use:

Since its launch in 1996, the MSP430 series of microcontrollers has always taken ultra-low power consumption as the family gene of the product, providing a wealth of low-power intelligent peripherals for the low-power design of the product. Due to the high frequency of use, the infrared body temperature detector has high requirements on the battery-powered battery life and the frequency of use, so the low-power operation of the thermometer has become a key challenge in system design.

A rich product family provides flexible memory options:

MSP430 series microcontrollers provide more than 16KB of on-chip memory, which can meet the memory requirements of most thermometer products. The rich product family of this series also provides a variety of memory options up to 512KB. Users can choose different memory sizes and quickly migrate existing designs without excessive workload. Recommended product models for thermometers are:

Table 1 Recommended models of infrared thermometer MCU products

The scheme in Figure 1 also includes TI’s extensive power management, signal chain and sensor products.

TPS61099 series chips are boost chips specially designed for applications requiring ultra-low power consumption. First of all, the static power consumption is only 800nA, and the input voltage is as low as 0.7V, which can perfectly support single-cell dry battery power supply. At the same time, when the input is 1.5V, the output is 3.3 The efficiency of 80% can be achieved under the condition of V/10uA. The TPS61099x series chips provide two kinds of output adjustable version and output fixed version for customers to choose. The fixed version supports almost various common output voltages from 1.8V to 5.0V.

The TPS62170 buck converter provides low IQ, which helps extend the battery life of the system, especially when the system is not in use. In addition, it supports high efficiency at switching frequencies above 2 MHz to help designers reduce the size of the inductors required, thereby reducing the size of the overall solution.

The TLV333 op amp is TI’s zero temperature drift op amp series, featuring high precision and low power consumption. On the one hand, the op amp’s ultra-low input offset voltage (15 µV max) and low temperature drift (0.02 µV/°C help minimize temperature sensing errors, and its rail-to-rail input/output performance helps maximize dynamic range. On the other hand, Low quiescent current (28 µA max), low voltage (1.8V to 5.5V) and small package size (minimum SC70 package), plus -40°C to +125°C operating temperature range, ideal for handheld or battery powered Medical equipment. In addition, the op amp series is also available in dual channel (TLV2333) and quad channel (TLV4333).

Faster settling times and lower noise may be required in some systems to help speed up temperature measurements. For these cases, OPA388 is a good alternative to TLV333. The OPA388 will provide lower input offset voltage (5µV max), lower noise (7 nV/rt(Hz)) and faster settling time (2µs), all of which will help minimize settling time and the required number of averaged samples to achieve the specified temperature resolution.

TI has a variety of op amps that can be used to interface signals between analog sensing elements and ADCs. The table below lists other amplifiers that can be used for this design, all in dual packages.

Table 2 Recommended operational amplifiers for signal interface

TI offers a variety of temperature sensors, our high precision digital sensor TMP117x has an accuracy of ±0.1°C over the -20°C to 50°C range. The device integrates a 16-bit resolution ADC that communicates with the designer’s digital controller via I2C or SMBus. The device is designed for battery powered systems as it has only 150nA Iq consumption in shutdown and requires only 3.5µA per 1Hz conversion cycle. For systems with an integrated ADC in the MCU, TI also offers analog temperature sensors and thermistors. The LMT70 provides a voltage output that corresponds to temperature with a maximum accuracy of ±0.13°C between 20°C and 42°C. For cost-sensitive systems, the TMP61 linear thermistor provides 1% temperature tolerance and simplifies the calibration process using traditional NTCs. For more cost-sensitive digital temperature sensing applications, TI’s TMP1075 can be used, which has ±1°C (max) accuracy over the −25°C to +100°C range. For systems that integrate an ADC in an MCU, TI also offers analog temperature sensors, and the TMP23x offers extensive design flexibility as designers can choose from ±0.5°C to ±6°C in accuracy and gain.

A low noise, sensitive voltage rail is usually required for powering the ADC and sensing elements. Low dropout regulators (LDOs) are a common choice for their ease of use and their ability to provide clean, low noise power to sensitive analog power rails. For this specific need, the TPS7A20’s ultra-low noise (6 µVRMS), high ripple rejection (85db @ 1 kHz), and low quiescent current (6 µA typical, 150nA in shutdown) make it the best choice . This provides the required low noise rails for the ADC and sensing elements (with little inherent output noise while filtering DC/DC ripple), while also providing low quiescent current for battery powered applications (extended battery life). For battery power systems, the TPS7A02 is another good choice, as it provides nanowatt-level IQ (25nA, 3nA in shutdown) while also providing high PSRR for post-DC/DC regulation. The TPS7A02 also has excellent transient response, which is critical for duty cycle loads.

There are some high-end products on the market that also include Bluetooth Low Energy (BLE) communication modules. If you are interested in adding it to your system, the CC2640R2F IC or CC2650MODA module is a great fit. TI’s SimpleLink™ software can help designers complete the development process as quickly as possible.

To reduce current consumption, load switches with integrated faults such as TPS2051x, or TPS22916xx with ultra-low leakage current, can also be used to disconnect the BLE module from battery power or any other DC power source. This extends the battery life of the product while adding other features to the user.

The TI devices detailed in this article will help designers quickly design infrared thermometers. TI values ​​the customer’s work to design and manufacture this end device with the support of our global manufacturing sites, while continuing to provide high-quality design assistance and excellent customer support.