BioSense Physiologic Sensing and Interface Board
The BioSense is a very extensible, fully-integrated physiologic sensing board that interfaces with the SAK2 via the low-profile, board-to-board connector, and is intended to support long-term health monitoring and activities of daily living applications.
BioSense Daughterboard Specifications:
- PIC18F877A 20-Mhz PIC microcontroller 14-bit processor with 8KB FLASH program memory, 3 Bytes RAM , 256 Bytes EEPROM. This processor is equipped with a full set of analog (10-bit) and digital inputs, on-board hardware multiplier, timers, compare/capture/PWM modules, in-system flash programming, and is supported by a wide range of development tools.
- 3D accelerometer based on the ADXL202JE sensor capable of measuring accelerations 1 2 G in 3 axes of motion, capable of accurately identifying accelerations over most of the range of normal human motion.
- 1 EKG channel: electrocardiogram via the INA321 differential instrumentation amplifier, capable of amplifying the potential generated by the heart (on the order of millivolts). The EKG can also serve as a single channel EMG (electromyogram) sensor for measuring muscle activity.
- 1 GSR channel: Galvanic Skin Response capable of measuring skin conductance changes over large excitation levels with tunable trimpots for tonic level adjustments (typically between 0.5 to 3 micro-siemens for a relaxed individual). This GSR was benchmarked against gold-standard GSR equipment used by psychotherapist researchers, with a high degree of concordance.
- 3 OPA4336 operational amplifier channels: for temperature or other analog sensors (default leadset includes the LM35 precision temperature sensor capable of of 0.25 :C resolution over a temperature range of -55 :C to 150 :C. Amplifiers can also be daisy-chained via jumpers to provide additional amplification stages for small-signal sensors (a piezoelectric strain respiration sensor capable of measuring sub-millimeter resolution displacements utilizes this amplifier chain).
- 4 additional general purpose analog channels that can be interfaced to a variety of other analog signal devices.
- Serial-to-I2C Converter: A preponderance of medical diagnostic devices output their data using the RS-232 protocol, which can be attached to the serial interface of a host computer. As such, the physiological sensing board breaks out the I2C and RS-232 lines, which allows us to connect any type of third-party RS-232 based sensors to the MIThril I2C sensor network with only a patch in the firmware. Currently the finger pulse-oximetry and portable blood pressure sensor are being interfaced through this pathway into our sensor network.
- High-insertion cycle, locking Hirose connector as an integrated leadset connector for EKG/GSR/sensors with virtual ground, ground, and power.
- B2B connector to attach to the SAK2 board. This low-profile connector breaks out 5V and 3.3V regulated power, I2C, RS-232, and analog/digital I/O channels from the microcontroller.
7Programming port for easy in-system programming. The SAK2 can optionally be programmed on-the-fly through its serial port as well.
- 2.5V bias reference voltage: (used by the EKG amplifier)
With the combined physiological sensing board and third-party sensors, a fully outfitted Wearable System can simultaneously monitor and record 3D accelerometer, audio, EKG/EMG, galvanic skin response, temperature, respiration, blood oxygen, blood pressure, heat flux, heart rate, IR beacon, and up to 128 independently channeled environmental activity sensors.
BioSense Design Files
BioSense Board Schematics
BioSense Board Composite Layout
BioSense Board Components Front
BioSense Board Components Back
BioSense Board Firmware
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Michael Sung