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Transcript
The Mica Sensing Platform Alec Woo Jan 15th, 2002 NEST Retreat Goal Need a set of different sensors to support A “mega” sensor board common sensing applications potential NEST specific applications Flexibility to select what sensors to populate rather than building many specialized sensor boards Under the constraints of Physical size, structure “Pin” estate Energy consumption Cost Outline Goal Board overview Hardware Interface Tour of individual components Components Selected sensors for the MICA sensor platform Photo (light) sensor Temperature sensor Microphone Single Tone Sounder 2 Axis Accelerometer 2 Axis Magnetometer Each module is independent Board Size 4-Layer Board same dimension as the Mica board make space for Mica’s switch and LEDs with a ground plane Top and bottom 51 pin connectors Stay on the top of a stack of daughter cards Device Placement Microphone Sounder Magnetometer 1.25 in Temperature Sensor Light Sensor 2.25 in Accelerometer Hardware Interface Mica PINS PHOTO SOUNDER Mic Signal MICROPHONE TEMP Y Axis X Axis Tone Intr Gain Adjustment MAGNETOMETER ADC Signals (ADC1-ADC6) On/Off Control I2C Bus Interrupt Y Axis X Axis ACCELEROMETER Outline Goal Board overview Hardware Interface Tour of individual components Photo Sensor Photoresistor Clairex CL9P4L Simple voltage divider design INT1 PHOTO ADC1 Temperature Sensor 2 options for thermistor High Precision, less range Low Precision, more range YY14406 10kohm, +/- 0.2 Co, ranging 0-75Co Expensive: $6/unit ERT-J1VR103J 10kohm, 1Co accuracy, -40 to 125Co $0.43/unit @1000 Voltage Divider Design Microphone Acoustic input with omni directional microphone Panasonic WM-62A draws < 500uA Flat frequency response from 100Hz to 5kHz 100Hz to 16kHz from spec Amplification and Filtering Pre Amp mic_out Fixed amplification of -56 Passive bandpass filters ~4.7mA for circuit prototype Amp Pre-amplifier (MAX 4466) Passive RC High pass and Low pass filters 159Hz – 6.4kHz + microphone Amplifier (MAX 4466) Adjustable amplification from -5 to -56 Sounder Now, we can make sound! Great for tracking nodes, debugging, application user interface, or ranging through time of flight Alternative design Power amplifier with a generic speaker Large energy consumption Potential influence on magnetometer Sounder Piezoelectric single tone buzzer Resonant at 4kHz +/- 0.5kHz 85dB sound pressure at 10cm Circuitry + sounder draws ~2mA Active Bandpass Filter mic_out Biquad Active Filter Circuitry P. 278, The Art of Electronics Tunable Active Bandpass Filter mic_bandpass_out center frequency(fo) and bandpass bandwidth (BW) Bandpass bandwidth determines quality of the filter Center frequency can shift while bandpass bandwidth remains the same fo = 1/2RFC BW = 1/2RBC Default setting Center frequency is 4kHz with 800Hz bandwidth Detecting the Sounder’s Signal National LMC567 Phase lock loop and adjustable amplitude threshold support to detect tone Adjustable tracking frequency Track either the output of the microphone or active bandpass filter Detector’s Output Raise an interrupt if tone is present Phase lock loop filter can be sampled directly to obtain information estimate time of flight with time synchronized RF signal Accelerometer Analog Devices ADXL202E 2 Axis, +/- 2g, at 2mg resolution 600uA current consumption Two types of output Raw analog output Duty cycle output Directly connected to Mica’s ADC channels Not used but signals are fanned out to pads on board $15/unit Magnetometer 2 Axis Honeywell HMC1002 Range is +/-6 gauss (earth’s field +/-0.5 gauss) 27ugauss at 10Hz Current consumption is ~5mA 2 stage amplification 29 * 41 = 1189 2 digital potentiometer to adjust 2nd stage amplification to avoid railing on each axis Amplifiers are not Rail-to-Rail (0.66V to 2.33V) Pads on board to allow easy access to demagnetize the chip $20/unit Further Information http://www.cs.berkeley.edu/~awoo/micasb Schematics Layout Gerber files Bill of Materials Delivery 30 boards on Feb 5th Crossbow ready around March 1st 1) basic sensors 2) basic sensors + magnetometer + accelerometer Signal and Power Interface Sensors or Actuators Signal Light Temperature ADC1 ADC1 Sounder - Microphone PLL Signal ADC2 ADC2 Tone Detector INT3 Accelerometer Magnetometer ADC3,4 ADC5,6 Power Control INT1 INT2 PW2 MUX Setting PW3 PW3 PW6 = 1 PW6 = 0 PW4 PW5