The Mica Sensing Platform Alec Woo Jan 15th, 2002 NEST Retreat

Goal Need a set of different sensors to support common sensing applications potential NEST specific applications A “mega” sensor board 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 same dimension as the Mica board make space for Mica’s switch and LEDs 4-Layer Board with a ground plane Top and bottom 51 pin connectors Stay on the top of a stack of daughter cards

Device Placement 2.25 in 1.25 in Microphone Accelerometer Light Sensor Temperature Sensor SounderMagnetometer

Hardware Interface PHOTO TEMP MAGNETOMETERACCELEROMETER MICROPHONE SOUNDER Mica PINS ADC Signals (ADC1-ADC6) I 2 C Bus On/Off Control Interrupt X Axis Y Axis Gain Adjustment Mic Signal Tone Intr

Outline Goal Board overview Hardware Interface Tour of individual components

Photo Sensor Photoresistor Clairex CL9P4L Simple voltage divider design PHOTO ADC1 INT1

Temperature Sensor 2 options for thermistor High Precision, less range YY kohm, +/- 0.2 C o, ranging 0-75C o Expensive: $6/unit Low Precision, more range ERT-J1VR103J 10kohm, 1C o accuracy, -40 to 125C o 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-amplifier (MAX 4466) Fixed amplification of -56 Passive bandpass filters 159Hz – 6.4kHz Amplifier (MAX 4466) Adjustable amplification from -5 to -56 Pre AmpPassive RC High pass and Low pass filters Amp mic_out ~4.7mA for circuit prototype + microphone

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 Biquad Active Filter Circuitry P. 278, The Art of Electronics Tunable center frequency(f o ) and bandpass bandwidth (BW) Bandpass bandwidth determines quality of the filter Center frequency can shift while bandpass bandwidth remains the same f o = 1/2  R F C BW = 1/2  R B C Default setting Center frequency is 4kHz with 800Hz bandwidth Active Bandpass Filter mic_out mic_bandpass_out

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 Directly connected to Mica’s ADC channels Duty cycle output 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 = digital potentiometer to adjust 2 nd 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 Schematics Layout Gerber files Bill of Materials Delivery 30 boards on Feb 5 th Crossbow ready around March 1 st 1) basic sensors 2) basic sensors + magnetometer + accelerometer

Signal and Power Interface Sensors or Actuators SignalPower Control MUX Setting LightADC1INT1 TemperatureADC1INT2 Sounder-PW2 MicrophoneADC2PW3PW6 = 1 PLL SignalADC2PW3PW6 = 0 Tone DetectorINT3 AccelerometerADC3,4PW4 MagnetometerADC5,6PW5