a potentiometer
/ poh-ten-shee-OM-eh-ter /
A potentiometer is a resistor with a movable tap — a knob or slider that picks off a voltage somewhere between two ends. Imagine a long strip of resistance with a wiper you can slide along it. Connect the two ends across a voltage and the wiper taps a fraction of that voltage depending on where it sits. As a position sensor, this is beautifully direct: the shaft angle or slider position becomes a voltage with no amplification needed at all.
Inside is a resistive track (carbon, cermet, or wirewound) with a wiper that contacts it. As a three-terminal device it is an adjustable voltage divider: with the track across a supply Vs, the wiper voltage is Vs times (fraction of the way along) — turn the knob a third of the way and you get a third of the supply. Used with only two terminals (one end plus the wiper) it is simply a variable resistor or rheostat. Pots come in linear taper (voltage proportional to angle, for sensing) and logarithmic taper (for audio volume, matching how we hear loudness). A multi-turn pot trades range for fine resolution.
Why this matters: as a position transducer the potentiometer is the cheapest, simplest one going — it sits behind volume knobs, joysticks, throttle and pedal sensors, and machine feedback. Read it ratiometrically (power the pot and the converter's reference from the same supply) and the reading depends only on position, not on the exact supply voltage. The honest caveats: the wiper physically rubs the track, so it wears out, grows noisy and scratchy with age, and can momentarily lose contact; and you must not load the wiper with a low resistance, or the divider sags and the reading goes nonlinear. For wear-free position sensing, a Hall-effect or optical sensor is the modern alternative.
A 10 kΩ linear potentiometer across 3.3 V acts as a throttle. At the halfway position the wiper sits at 3.3 V times 0.5 = 1.65 V; at three-quarters travel it reads 3.3 V times 0.75 = 2.48 V. The converter reads angle as voltage directly — no amplifier, no bridge.
Position becomes a voltage directly — a voltage divider you can turn.
The wiper is a mechanical sliding contact: it wears, gets noisy with age, and must not be loaded by a low resistance or the divider sags into nonlinearity. For long-life, wear-free position sensing, use a contactless Hall-effect or optical sensor.