Hardware lab 06 · Analog timing input

A paddle becomes a time interval.

Turn the potentiometer, discharge the capacitor, and count clock ticks until an analog voltage crosses a comparator threshold.

VC(t) = VS × (1 − e^−t/RC)potentiometer position → resistance → RC time constant → threshold time → timer count → angle

LIVE INSTRUMENT

RC timing bench

IDLE

Keyboard: ←/→ turn one degree · Space trigger · P pause · N step · C instant capture

Nominal values are what the schematic promises. Error sliders represent the actual component landing somewhere inside its tolerance band.

Paddle shaft135°

Potentiometer maximum1000 kΩSeries protection R4.7 kΩNominal capacitance47 nFPot actual error3.0%Cap actual error-6.0%Comparator threshold2.50 V

The comparator is analog, but the recorded result is discrete: the first timer edge after the crossing.

Timer clock1000 kHzTimer width16 bitDischarge switch R100 ΩDischarge pulse500 µs

READY

Timing fits the counter, discharge is complete, and useful count resolution remains.

TWO-POINT CALIBRATION

Turn fully counterclockwise, capture, then store the minimum.

Turn fully clockwise, capture, then store the maximum.

Counts between the endpoints interpolate to a calibrated angle.

Select a target, turn the paddle, then capture. Try to land within ±2° using only the timer-derived angle.

CAPTURE REQUIRED

#	Shaft	Actual R	Ideal time	Count	Quantization	Derived angle
No measurements yet. Trigger the discharge cycle.

The controller does not send an angle. It changes a resistance.
The capacitor converts resistance into elapsed time through an exponential voltage curve.
A comparator turns the analog threshold crossing into one digital edge.
The timer rounds that edge to a whole number of clock periods.
Part tolerances and threshold variation move the count even when the shaft does not move.
Endpoint calibration absorbs much of that unit-to-unit variation into software.