AnkleHardwareSpec2007Sep
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Contents
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
- Z axis rate gyro ADXRS300 (analog) or ADIS16100 (digital)
- 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.