The infrared thermometer was a critical line of defense during the pandemic. As soon as we resumed operations we began developing an infrared thermometer solution, and have since helped many customers reach mass production. While supporting our customers through mass production we have continuously refined the hardware, firmware and algorithms. The solution now supports a wide range of analog sensors and delivers reference-source calibration, thermopile voltage-drop calibration, ambient temperature compensation and offset compensation, along with multi-point calibration, user-defined alarm thresholds, storage and retrieval of measurement records, offset setting, body/object mode switching and unit switching.
Solution Overview
Solution 1: ZML166 is used as the main MCU. The chip integrates a 24-bit Σ-∆ ADC, a 128x high-impedance input amplifier and a voltage reference, putting the complete infrared sensor measurement circuit on a single chip, which makes it ideal for high-precision analog conversion applications. An external LCD driver drives the display, one I/O provides a PWM output to sound the buzzer as a prompt, and one I/O detects the measurement key. Combined with the power-on circuit, this key also serves as the power-up button; once the unit is powered up the MCU takes over power control and switches the unit off automatically when the measurement is complete, optimizing power consumption. Besides the measurement key, three further keys are needed to switch system functions: one to switch units (Fahrenheit / Celsius), one to switch mode (body mode / object mode), and one to browse stored measurements. An EEPROM stores the temperature records and the calibration data, holding 32 temperature readings by default. The functional block diagram is shown below; ZLG72128 or another LCD driver chip can be selected to drive a segment LCD or an LED digit display.
Solution 2: the system uses the HDSC HC32L136K8TA as the main MCU. This chip has a built-in LCD driver peripheral and can drive the LCD display directly. Four ADC channels acquire the sensor parameters, two of them via an op-amp stage; one I/O provides a PWM output to sound the buzzer as a prompt, and one I/O detects the measurement key. Combined with the power-on circuit, this key also serves as the power-up button; once the unit is powered up the MCU takes over power control and switches the unit off automatically when the measurement is complete, optimizing power consumption. Besides the measurement key, three further keys are needed to switch system functions: one to switch units (Fahrenheit / Celsius), one to switch mode (body mode / object mode), and one to browse stored measurements. An EEPROM stores the temperature data and the calibration data, holding 32 temperature readings by default. Bluetooth can also be added, allowing the data to be sent to a phone for statistics and management. The system is powered by two dry cells, stepped up to 3.6V by a DC-DC converter and then regulated to 3.3V by an LDO.
Recommended MCU
- ZML166 series: ZML166 — M0 core with rich peripherals, 64K flash and 8K RAM; on-chip op-amp and a built-in 24-bit high-precision ADC, delivering single-chip high-precision analog-to-digital processing
- HC32L series: HC32L136 — M0+ core with rich peripherals, 64K flash and 8K RAM; built-in LCD driver and 12-bit ADC, so no external driver is required; multiple power modes with only 0.4μA consumption in deep sleep
Core Components
- LCD driver: NXP, full part number available on request
- MCU: ZML166 (ZLG Microelectronics)
- MCU: HC32L136 (HDSC)
- LDO: ZL6205 (ZLG Microelectronics)
- LED digit display driver: ZLG72128 (ZLG Microelectronics)
- Op-amp: 3PEAK, full part number available on request
- EEPROM: onsemi, full part number available on request
- DC-DC: MPS, full part number available on request
Reference Design
- Mature demo unit;
- Development documentation in Chinese;
- Full technical support;
- Schematic and PCB reference design;
- Infrared thermometer application note;
- Peripheral example code and supporting documentation;
- Infrared thermometer algorithm library;
- Complete demo programs
- Support for sensors from multiple manufacturers
Functional Block Diagram
