Newton measured as change in capacitance between

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Unformatted text preview: es Designed for a maximum g-force (e.g., 2-10g) 2-axis and 3-axis versions Used in airbags, laptop disk drives, etc. $ $ ! Analog output too susceptible to noise Digital output requires many pins for precision Use pulse-width modulation What about gravity? $ !; , 2-axis accelerometer Set 0g at 50% duty-cycle Positive acceleration increases duty cycle Negative acceleration decreases duty cycle 12.5% per g in either direction , !; , Cause interrupts at Ta, Tb, and Tc from X-axis output 1. Look for rising edge, reset counter: Ta = 0 2. Look for falling edge, record timer: Tb = positive duty cycle 3. Look for rising edge, record timer, reset counter: Tc = period Repeat from 2 Same for Y-axis output (T2 is the same for both axes) Noisy data – all forces are aggregated by accelerometer Sample trace at 250Hz Walking down six flights of stairs !; Elevator ride " ' 8 ( +$ . < = /$ % Average over time – smoothing Filter capacitors limited noise frequency Software filter – like switch debouncing bandwidth limiting Take several readings use average for Tb and Tc or their ratio Running average so that a reading is available at all times e.g., update running average of 4 readings current average = ¾ * current av...
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