Make a simple smartwatch that offers ambient and skin temperature monitoring
When we look at the current wearable hardware landscape, these devices stuff a lot of sensors that make them smart. These integrated sensors include an accelerometer, heart rate, temperature, and more. Here is an example of a simple smart watch that offers ambient temperature and skin temperature monitoring.
Tracking ambient conditions is useful for applications such as in a smart home to automatically control the indoor temperature and optimize it to personal preferences. Skin temperature sensor is another relatively simple sensor that’s used in smartwatches to report bio-data. This sensor can help you in determining exertion levels such as while exercising when you compare the skin temperature to ambient temperature.
Human Skin Temperature Sensing Wristwatch
The objective of the LMT70 Wearable Design is to show how to design and mount a small form factor electrical system that fits inside a smartwatch or fitness tracker that measures both human skin and room temperatures with an accuracy of 0.1°C in the human body temperature range of 20°C-42°C.
To achieve these objectives the LMT70 analog temperature sensor, ADS1115 analog-to-digital converter, and the MSP430G2553 microcontroller were implemented together as the signal path.
The MCU converts the LMT70 data into an accurate temperature value, which will be displayed in the LCD screen.
The remote PCB is a very small PCB with only the skin temperature sensing LMT70 and supporting thermal devices such as copper pads and thermal vias are used primarily to sense skin temperature. These two boards are connected with the J2 connector.
The signal path of this device starts with two LMT70’s, one for measuring the skin temperature and another one measuring for the ambient/board temperature. Both devices are connected to two channels on the ADS1115 ADC.
From the analog to digital converter, the data is sent through an I2C interface to the MSP430G2553 microcontroller for further processing.
Click here for the reference design.