P11011: Modular Motion Tracking Knee Flexion Unit V1

Button Current Flow

Button Current Flow

Before selecting a pushbutton switch for the head motion sensor, the maximum current and power that could flow through the button were calculated. The USB standard sets the allowed voltage within their system at within 5% of 5 V. In the worst case scenario, the voltage would then be at 5.25 V. The ATmega328 has an internal pull-up resistor that has a value from 20 kOhm to 50 kOhm. The worst case scenario would have this value at 20 kOhm. The maximum current flowing from the top rail, through the pull-up resistor, and through the button to ground would be:
I_max = V_max / R_min = (5.25 V) / (20 kOhm) = 0.263 mA at 5.25 V
P_max = (0.263 mA) x (5.25 V) = 1.38 mW

All pushbutton switches that we examined met this set of criterion.

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