CogWatch: An open-source platform to monitor physiological indicators for cognitive workload and stress

Fig. 1. Block Diagram of Cogwatch Components.

Fig. 2. Wheatstone Bridge and Differentiator to measure GSR. The GSKIN port allows for selection of sensors so GSR can be measured from wrist, fingers, or any other location desired.

Fig. 4. A) CogWatch Main Board. The test point for 1.8 V is shown in the blue box and pads to be joined by solder are shown in the purple box. B) The Sensor Board carries the PPG, 6DOF IMU, and Magnetometer. It allows for the PPG unit to have direct skin contact. The solid gold circles are test points to validate that pads on the IC components have not been bridged.

Fig. 5. A) Typical output on SCL pins in connected state. The lines for the 3 V and 1.8 V connections are all shown on same scale and should have identical waveforms when device is on, but data is not being transmitted. B) Output from the I2C_Scan app showing expected devices connected.

Fig. 6. A) The battery port shown circled in Blue and GSR port in Yellow, B) placeholder for wrist mounted GSR sensors, C) placeholder for GSR sensors on fingers.

Fig. 7. A) Devices and Printers shown in Green Box, B) Bluetooth Device name shown in green box, double click the icon and select the services tab to find the COM port circled in Yellow Box, C) if using standard USB connection then the device will be listed under ‘Unspecified’ and com port will be listed in its name as shown for device in Green Box.

Fig. 8. A) Update lines circled in yellow to allow connection to your local WiFi network, B) Insert timestamp as shown in green box, C) the ‘a’ command can be sent to query device to ensure that it is working and give a list of attached sensors.

Fig. 3. Assembly Flowchart.

Fig. 9. A) shows calculated heart rate based on ECG (Zephyr 3.0 ground truth), B shows PPG (CogWatch) predicted heart rate, Figures C and D show the multimeter measurement of kOhm vs the values registered on the ADC of the ESP32 for selected resistor readings. Fig C highlights min/max in light blue and D shows the standard deviation light blue. It should be noted that both were negligible.

Fig. 10. Simultaneous temperature measurements on room temperature water with a thermocouple and the MLX IR temperature sensor. It can be observed that the MLX IR temperature sensor is more consistent in its measurements.