Sunday, May 26, 2024

Skin Temperature Measurement Reference Design

The design uses a temperature sensor and BLE MCU for skin contact measurements, offering two modes: a long shelf life and iOS device monitoring.

thermometer

A new solution has emerged in response to the growing demand for integrating sensors with modern wireless and cloud technologies. The Bluetooth-enabled high-accuracy skin temperature measurement flex patch offers a convenient wireless method for obtaining precise skin temperature readings. These readings can be seamlessly transmitted to Bluetooth-compatible devices like smartphones or tablets.

The TIDA-01624, a reference design from Texas Instruments (TI), utilises the TMP117 high-accuracy, low-power, digital temperature sensor, which makes direct contact with the skin. It sends 16-bit digital output data via I²C to the CC2640R2F SimpleLink Bluetooth low energy (BLE) wireless microcontroller (MCU). The CC2640R2F then transmits this data to a Bluetooth-connected device using Bluetooth protocol. 

The patch is designed for low power consumption, with a 3-V, flexible thin-film battery. For testing and demonstration, designers can power the device externally using its large contact pads when a battery is disconnected.

The patch has two primary modes: active and inactive. In inactive mode, the CC2640R2F shuts down completely, and the TMP117 powers down, enabling the patch to last multiple years without significant battery drain. Activating the patch by pressing the wake-up switch switches it to active mode, where the TMP117 starts reading and auto-advertising temperature data for the CC2640R2F BLE device.

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The power must be removed and reapplied to switch the patch from active back to inactive mode. This design is intentional for healthcare applications, where reusing monitoring patches could pose patient hygiene risks. The patch is designed to be disposable and used only once. An alternative for temperature monitoring is using a removable covering, similar to probe-type thermometers for oral temperature measurements. In such designs, the final design must characterise the system and covers. For probe-based systems, software modifications can allow switching between modes, but an MCU with Bluetooth communication capabilities is required in the probe.

The design applies in various fields, including medical devices, healthcare, and wearable technology. It offers versatile solutions tailored to these sectors, enhancing their capabilities and efficiency.

The design boasts several key features, including high accuracy (±0.1ºC) temperature measurement specifically tuned for human body temperatures. It comes equipped with a 2.4-GHz RF transceiver, compatible with Bluetooth low energy (BLE) 4.2 and 5 specifications, ensuring reliable and up-to-date wireless communication. A flexible PCB enhances the design with an integrated PCB antenna, adding versatility. Additionally, the device offers an impressive shelf life of up to three years and a five-day active use period. To complement these features, an iOS app is available for convenient device monitoring.

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TI has tested this reference design. It comes with a Bill of Material (BOM), schematics, Gerber file, Printed circuit board (PCB) layout, computer-aided design/ computer-aided engineering (CAD/CAE) symbols, etc. You can find additional data about the reference design on the company’s website. To read more about this reference design, click here.

Nidhi Agarwal
Nidhi Agarwal
Nidhi Agarwal is a journalist at EFY. She is an Electronics and Communication Engineer with over five years of academic experience. Her expertise lies in working with development boards and IoT cloud. She enjoys writing as it enables her to share her knowledge and insights related to electronics, with like-minded techies.

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