Revision as of 23:33, 14 September 2007

State Machine (Master) Controller

• 25.38V max supply voltage (6 cell LiPoly)
• IIC EEPROM for controller parameters (24LCxx)

Off board interfaces

Switch Input

• external logic switch input for mode control

External Serial Communication and ISP

• Ability to support a variety of attached serial devices: wired RS-232, Bluetooth, 802.11, and ISP.
• 1Mbaud (max) RS-232 level ASYNC serial (Tx, Rx, RTS, CTS) :
• Power for external devices: 5V and Vbat (with 0.25amp self resettable fuse)
• ISP signals (PGC, PGD, MCLR) for external ISP
• signals: Vbat, Vcc5, GND, Tx, Rx, RTS, CTS, PGC, PGD, MCLR

Power / Data to Motor Controller

• logic level ASYNC 2-wire serial between SM and motor controller CPUs
• logic level output to motor controller fault pin to disable PWM
• logic level input for motor controller alert status
• (Vbat) battery power from motor controller
• sense path to battery for voltage monitoring
•  ??? board to board stacking connector (more reliable that wires)

Strain, SEA, Motor Temp, Supply current

• 4 analog inputs to CPU, DC to 500 Hz analog bandwidth
• 1 x 10k(or more) thermo resistor (requires opamp follower) : AGND and signal
• 2 x strain gauge bridges (340 or 1k ohm) to high gain INA326 : AGND, SG+, SG-, bridge reference
  • SG bridge reference voltage through 0.1% resistance (1k to reduce bridge current) ideally from AVCC3.3 (ADC reference) or from AVCC5
• 1 x analog input for SEA hall sensor board (no voltage or current amp required) : 3.3V, AGND, signal

Pager Motor

• 3 pin header
• ability to turn on/off pager motor (3.3V)

On board sensors

Ambient Temperature

• Thermo resistor (>=10k) with opamp follower placed very close to XY axis IMU (or epoxied to XY sensor)

Supply Voltage Monitor

• (better than) 1% accurate measurement of battery voltage (prevent over-voltage during regeneration)

IMU

• 3 DOF accelerometer, 2 DOF rate gyros
• 3axis (SPI) accelerometer LIS3LV02DQ
  • this sensor will be (nearly) always powered and used to wake the processor

• XY axis (analog) rate gyro IDG300
  • Note: XY is in circuit board plane

AVCC5 monitor

• If SG bridge is powered from AVCC5 then we need to measure AVCC5/2, and SG bridge offsets depend on AVCC5

LEDs

• 2 LEDs mounted so as to be externally visible

Low Power Support

• Design for overall low power
• Target for sleep power of 5mW (0.12WHr/day - from VBAT), processor is sleeping.
• RS232 output interface disable (Rx still active - SN75C3223)
• Control of supply to internal sensors : ambient temperature, IMUs
• Control of supply to external sensors : ankle angle, SG, SEA, motor temperature

Sensor Power

• EC30 MR-ENC 15.5mA @ 5V : 77.5mW
• EC30 HALL SEN 10.6mA @ 5V : 53mW

• SG : 73mW(340ohm/5V), 10mW (1k/3.3V), 2.7mW(1k/1.6V)

• IDG300 9.5mA @ 3.3V : 31.mW
• ADXRS300 6-8mA @ 5V : 35mW
• ADIS16100 7-9mA @ 5V : 40mW

• ADIS16006 1.5-1.9 @ 3-5V : 5 mW
• LIS3LV02DQ 0.6-0.8 @ 2.2-3.3V : < 2.6mW (has programmable acceleration alarms to wake CPU)
• ankle angle pot : 0.1-1mW

• Power supply (LT3470) efficiency 70%>5mA, 60%@1mA, 35%@0.1mA, (0.6mW from Vbat when LT3470 enabled)

software

• ability to reprogram controller over ASYNC serial
• 2 DMA controllers run the two ADC units at 12 bits, 400 KHz total sample rate
• Input capture measures PWM period of magnetic rotary encoder / QEI captures encoder position
• DMA controller sends/receives SPI to digital accelerometer
• Main code loop runs at 500 Hz
  • decimation of analog inputs
  • reads ankle position
  • reads IMU, estimates orientation
  • reads motor controller status (motor current, motor position, status)
  • processes external communication interface

deep sleep / sleep / initialization

• when entering a sleep state, some parameters may be written to EEPROM. Specifically the SG offsets will be checked against the stored value, and updated if the offset changes "significantly".

deep sleep

• (<10uA, <0.25uW) when battery is near death. Disconnect as much of the system as possible from battery.
• motor leads are shorted with "zero power"

sleeping

• (<10mW) when ankle is inactive for period of time

• the motor controller is is very lower power state (only activity is listen on Rx), motor leads shorted

• On SM only the accelerometer is active (all other sensors are unpowered)
  • the accelerometer is programmed to generate an interrupt on certain acceleration conditions
  • the CPU will periodically (10Hz) awake and check the state of the accelerometer and conditionally enter a "mid-power" state to test other sensors.
  • if sensors suggest the ankle is active, the initialization state is entered

initialization

• state entered upon connection of battery is attached or when waking from sleep
• all sensors and hardware are powered, but motor leads remain shorted
• SM will watch for a transition from ankle on ground (loaded) to ankle in the air.
  • shortly after ankle in the air the K3 strap will force the ankle into the zero position. The set point for the virtual spring is zeroed to this location
  • A small (1amp) current can be used to further guarantee the ankle is against the K3 strap.
  • strain gauges offsets can be zeroed at this point.
  • At this point the motor controller is commanded to enter current mode and the SM proceeds to normal operational mode.

Motor Controller

Motor