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Holtek Semiconductor is a leading professional IC design house in Taiwan having its major business activities focused in the area of microcontroller and peripheral component design and marketing. From its origins in 1998, the company has continuously focused its energies in the advancement of new product development and skills innovation.

Ref. Picture for Thermometer Testing

As per Global Forehead Thermometer market is valued at 91 million US$ in 2018 and will reach 130 million US$ by the end of 2025, growing at a CAGR of 4.7% during 2019-2025.


Health monitoring at home and in public places has become a critical requirement in these days. After the impact of epidemic, the world has drastically changed in its operations in public places by checking health conditions through temperature monitoring. So in such condition, requirement of fast and accurate temperature measurement plays an important role. The scale of using contactless thermometer is rising as it produces accurate readings within less time.

Compared with traditional mercury thermometers and electronic thermometers like axillary thermometer, forehead thermometers have the advantages of simple operation, rapid and accurate measurement and additionally are not required to touch the skin surface. Therefore, forehead thermometers have gradually become the mainstream product type in the thermometer market. In order to ensure rapid product development, HOLTEK provides technical information including block diagrams, application circuits, PCB layouts, component lists.

Holtek has developed the BH67F2742 which is a dedicated MCU for contactless infrared thermometer applications, such as forehead and ear thermometers which provides a variety of flexible functions and features. The MCU Flash architecture facilitates production parameter adjustment, product calibration and data storage. Compared with traditional solutions, the integrated LDO, EEPROM, LED and LCD drivers, low noise Operational Amplifier and 24-bit A/D Converter reduce the xrequirements for large numbers of external components.

Forehead Thermometer
Figure 1. Forehead Thermometer
Figure 2. Forehead Thermometer MCU Specifications

Thermopiles are designed to measure temperature from a distance by detecting an object’s infrared (IR) energy. The higher the temperature, the more IR energy is emitted. The thermopile sensing element, composed of small thermocouples on a silicon chip, absorb the energy and produce an output signal.

BH67F2742 has built-in LCD driver used to drive an LCD to display temperature. Buzzer and Motor are used for vibration and sound output alert when measurement is complete.

Forehead Thermometer circuit description

Figure 3
Figure 3. Thermometer Schematic

DC-DC Converter
The HT7733SA is a high efficiency PFM syn¬chronous stepup DC-DC converter. The device has the advantages of extremely low start-up voltage as well as high output voltage accuracy. It has higher operating frequency and also offers the advantages of much reduced audio frequency noise. The devices require only three external components to provide a fixed output voltage of 2.7V, 3.0V, 3.3V, 3.7V or 5.0V. The HT7733SA devices include an internal oscillator, PFM control circuit, driver transistor, reference volt¬age unit and a high speed comparator. These devices are available in space saving 3-pin SOT89, 3-pin SOT23 and 5-pin SOT23 packag¬es. For 5-pin SOT23 package types.

This device contains an LCD Driver function, with internal LCD signal generating circuitry and various options, will automatically generate these time and amplitude varying signals to provide a means of direct driving and easy interfacing to a range of custom LCDs. For large volume applications, which incorporate an LCD in their design, the use of a custom display rather than a more expensive character based display reduces costs significantly.


Figure 4
Figure 4. Thermopile


Figure 5
Figure 5. Thermopile Specifications

This device contains a high accuracy multi-channel 24-bit Delta Sigma analog to digital converter which can directly interface to external analog signals. PGA gain control, A/D converter gain control and A/D converter reference gain control determine the amplification gain for A/D converter input signal. The designer can select the best gain combination for the desired amplification applied to the input signal.

Switch, Buzzer and Vibration
Switch is used for ON/OFF operation as well switch is used for multipurpose operations to control thermometer while taking readings. To indicate completion of reading, vibration and buzzer indication are provided to intimate user the completion.

Figure 6
Figure 6. Device Specifications
Figure 7
Figure 7. Forehead Thermometer Module
Figure 8
Figure 8. Forehead Thermometer PCB

Advantages of Forehead Thermometer
A Forehead thermometer is a mercury-free, user-friendly, touch-free infrared type thermometer often used at home. It can accurately measure a person’s temperature within few seconds via the forehead by scanning the temporal artery blood flow. For this reason, it is a great tool to measure a body temperature.

Additional features such as the sound/silent button or an LCD blink alarm are attached for a high-temperature alert. Memory and advanced measurement functionality is available. Holtek supports with providing supporting circuitry design for development of this product. Holtek is mainly focusing on Application oriented MCU’s and few general MCU’s. We keep on evaluating the customer requirements in different segments like Industries, Consumers and Automobile Industries to provide better solution to customers.

For further technical and design development support, click here


Nitisha Dubey

I am a Journalist with a post graduate degree in Journalism & Mass Communication. I love reading non-fiction books, exploring different destinations and varieties of cuisines. Biographies and historical movies are few favourites.

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