SAK2 Sensor Hub and Interface Board Hardware Overview

The SAK2 (Swiss-Army-Knife 2) Board, is a very flexible data acquisition board that serves as the central sensor hub for the MIThril 2003 distributed system architecture. The SAK2 board was designed primarily to interface a variety of sensing technologies with mobile device-based wearable platforms to enable real-time context-aware, streaming data applications. The SAK2 is an extremely flexible data acquisition hub, allowing for a wide variety of custom as well as third-party sensors to interface to it. In addition to being a sensor hub, the SAK2 can also operate in stand-alone mode for a variety of long-term data acquisition and real-time interactive applications.

The final version of the SAK2 has already been put out for a production contract assembly run, and will be available in mid May, 2004.

SAK2 Specifications:

• PIC18F452 40-Mhz PIC microcontroller (up to 10 MIPS) 16-bit processor with 32KB FLASH program memory, 1.536 KB 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.
• LTC1625 Linear Technologies 5V synchronous high-efficiency step-down switching power regulator (5-36V input range). This high-efficiency power regulator accepts a wide variety of input voltage sources appropriate for wearable applications, including 4 AAA battery packs and Li-Ion/Li-Polymer batteries. Provides up to 2A of current at around 95% efficiency, which is necessary to support a sensor network along with the Zaurus (which can draw upwards of 1.5A assuming a depleted battery charging + WiFi activity + full-backlight + 100% processing power utilization). The regulator can also accept unregulated power through the MIThril bodybus network via the MIThril port if no other power source is available. A 3.3V regulated power is also generated (used by the Nordic tranceiver) and is also broken out to the B2B connector and MIThril port
• nRF2401 Nordic low-power 2.4 Ghz wireless RF tranceiver with on-board quarter-wavelength monopole antenna. Capable of megabit data rates and frequency hopping over 125 independently addressed channels over an effective range of 100 meters. This is used to access the variety of wireless sensors currently being developed at the lab, including the MITes. Details of the wireless protocol can be found here.
• CompactFlash connector which accepts both Type I and Type II CF memory cards as well as IBM Microdrives.
• DS1302Z Dallas Semiconductor real-time clock with 12-mm coin battery backup (provides date and time to second resolution, for time stamping sensor data. Finer-resolution time-stamping can be generated from internal microcontroller timing.
• MIThril port connector: providing serial/I2C/regulated and unregulated power/USB signalling to MIThril-compatible sensors and peripherals (accelerometers, IR tag readers). Arbitrary numbers of sensors can be connected to the MIThril sensor network through MIThril junctions.
• I2C serial port: Separate I2C port for peripherals on the I2C bus using high-insertion cycle Hirose connector. Supports up to 400 kbits/s in (Fast-mode).
• RS-232 serial: FPC-based connector (for interfacing with Zaurus) with an additional port connection which can be wired to a standard DB9 for PC-compatible (5V inverted) signalling. Supports up to 115.2 kbits/s data rates.
• B2B connector for sensor/expansion daughter cards. This low-profile connector breaks out 5V and 3.3V regulated power, I2C, RS-232, and analog/digital I/O channels from the microcontroller.
• Programming port for easy in-system programming. The SAK2 can optionally be programmed on-the-fly through it's serial port as well.
• Power connector with high insertion-cycle, locking Hirose connector with high current rating. This power connector includes the 1wire interface connected to the microcontroller to be able to monitor battery life and usage statistics.
• Bi-colored LED status light
• Board Size: 3.1 x 2.6 inches or 7.9 x 6.6 cm

The SAK2 Board was designed to be backward-compatible to the Hoarder Board, which was designed and implemented by Vadim Gerasimov. The specifications for the original design was co-developed by Vadim Gerasimov and Rich DeVaul.

Sensors/Peripherals

• BioSense Board: Physiologic sensing daughterboard (3D accelerometer, 1 channel EKG/EMG, galvanic skin response, 3 channel temperature/respiration/3rd party sensors). This board interfaces with the SAK2 via the B2B connector, and is intended for long-term health monitoring and activities of daily living applications.
• Multisensor2 Board: Providing a 3D accelerometer, IR tag, IR tag readers (vertical, for in-door location in place of GPS, and horizontal for peer or object identification), and audio microphone. Interfaced to the SAK2 via the I2C port. Contact Chris Elledge <celledge@alum.mit.edu> for more information
• IR Tag Reader: IR tag reader, to be used in conjuction with our Squirt IR Tags to identify tagged objects, people, or even locations (our labspace ceiling is arrayed with them to give us rough location with an accuracy of about a meter)
• Accel2 Board: 3D Accelerometer Board very useful for a variety of context-aware applications. We have demonstrated the ability to use a single accelerometer board to be able to accurately classify activity state (standing, walking, running, lying down, biking, walking up stairs, etc). Interfaced to the SAK2 using the MIThril port. We are currently in the process of interfacing other physiological sensors, such as a piezoelectric strain respiration sensor and ambient light sensors, into our sensornet framework.

  BodyMedia SenseWear: A wonderful sensor package which provides heart rate (via a Polar heart strap), galvanic skin response, 2D acceleromter, temperature (ambient and skin), and heat flux in a small form-factor package worn on the back of the arm. The SAK2 can interface to the SenseWear wirelessly via a 900-Mhz tranceiver attached to the serial-toI2C bridge (the tranceiver interface was discontinued in the SenseWear Pro 2)

• MITes Environmental Sensor: a wireless 3D accelerometer using the nRF 2.4 Ghz protocol has been developed by the house_n group at the Media Lab for wireless environmental sensors for monitoring human activities in natural settings. Contact Emmanuel Munguia Tapia <emunguia@media.mit.edu > for more information.
• Socio-Badges : Multifunctional boards with on-board DSP processor capable of processing audio features, RF tranceiver, IR transceiver, 5x9 brightness-controllabel LED output display, vibratory feedback, mavigator switch, flash memory, audio input/microphone and optional LCD display. This badge is meant for social-networking experiments and other interactive distributed applications.

Annotator Board: a button-based event-capture and audio annotation/labeling board. Contact Michael Sung <msung@media.mit.edu> for more information

Vibe Board: a haptic output device to provide vibro-tactile feedback. Contact Anmol Madan <anmol@mit.edu> for more information.

Resources

The SAK2 was designed and intended for general use by research groups at the MIT Media Laboratory as well as other research communities at large. The following links provide all the design files necessary to replicate the MIT Wearables Group's hardware setup. On the hardware side, we recommend the MPLAB 6.5 microcontroller development environment, the CCS compiler, and the PICStart Plus programmer. We support a variety of linux-based tools called Enchantment to stream data in real-time from the SAK2 hub through the 803.11b infrastructure (via the Zaurus or other linux-based device). We are currently working on a much cleaner, modular, and buffered version of the SAK2 firmware which should be available in May, 2004.

SAK2 Firmware

SAK2 Schematics

SAK2 Bill of Materials

SAK2 Board Components-Front

SAK2 Board Components-Back

SAK2 Board Layout Composite

SAK2 Board Production Files (Gerbers/NC Drills)

Host-side Interface API

Random Integration Notes