Final Design

The final design of the portable thermoregulation device consists of four major systems: power, control, temperature sensing, and TED cooling. The first three systems are all wired and housed within electronics enclosures. These electronics are connected to the TED via jumper wires running out the enclosures. The enclosures are clipped to the waist, while the TED (and the temperature sensor) are attached to the armband for the user to wear.

(Left) Top-down view of entire assembly with electronics and armband.

(Right) Armband being worn with the TED attached.

Circuit schematic of final design.

Power System

Components:

• • Battery

  • Low-pass LC filter

The power system is one of the most critical systems in the design: without it, the TED which the project is designed around would not operate. Thus, two LiPo batteries with high energy density were chosen and connected in series to power the controller and TED. The low-pass LC filter is designed to smooth out the pulse width modulation (PWM) signal sent from the Arduino to the driver, allowing the battery to act as a continuous DC voltage source rather than having it operate at full voltage in intervals. This reduces the Joule heating effect which leads to a higher thermal efficiency of the TED.

A 3.7V 1100mAH Lithium-ion Polymer (LiPo) battery pack used to power the Amicrocontroller and TED.

Control System

Components:

• • Arduino

  • Arduino code

  • Shield

  • BLE module

The Arduino is the microcontroller that runs the control loop code and sends signals to the shield, which facilitates powering to the connected electronics. The Bluetooth Low Energy (BLE) module allows for wireless operation via a mobile app for an ease-of-use interface between the user and the device.

(Left) HM-10 Bluetooth Low Energy (BLE) module for communication between phone app and Arduino.

(Right) Interface screen on phone app for communication to and from the Arduino.

Temperature Sensor System

Components:

• • RTD

  • Op amps

  • Resistors

  • Voltage references

The resistance temperature detector (RTD) is the sensor used in the device. Temperature is detected by correlating a change in temperature with the change in resistance of the RTD, which is determined by measuring the voltage across it via a forcing current generated by the op amps, resistors, and 4.096 V voltage references. This circuit is powered by the same LiPo batteries, ensuring the voltage references receive a high enough voltage to output 4.096 V.

Schematic of the circuit for sensing temperature (courtesy of Dr. Jerry Tustaniwskyj).

Cooling System

The cooling system contains the following:

• • Armband

  • TED

  • Electronics enclosures

The armband allows the user to keep the TED, which cools the user, in contact with the user's skin. The electronics are connected to the armband via wires that run out of enclosures to be clipped onto the waist.

3D CAD model of electronics enclosures. Interior of 3D printed electronics enclosures. Enclosures being clipped onto the waist.