The voltage divider is the first circuit that produces an in-between answer, and the potentiometer is the divider you can adjust without swapping parts. Today's build is small, but it introduces the most reusable idea on the bench: position becomes resistance becomes voltage.

Wire the divider

At sim.devoltapp.com, on a Breadboard (400) with the Bench PSU at 5 V:

1. Place a Potentiometer. It has three terminals: the two track ends (marked cw and ccw for the clockwise and counter-clockwise ends) and the wiper between them.
2. Wire one end to 5 V, the other end to ground, and the wiper to a free column. The wiper column is your output.
3. Run the simulation and tick the wiper node in the Analysis panel.

Now select the pot. Its Inspector card is a Position control: a rotary knob with a matching slider underneath (the slider is there so keyboard users get the same control, and honestly it is also easier for fine moves). Drag the knob slowly from one end to the other and watch the scope in Roll mode: the trace glides from 0 V to 5 V and back as you turn. The divider equation, Vout = Vin × (lower resistance ÷ total), is happening under your cursor in real time.

Park the knob at 50% and the wiper reads 2.50 V. At 25%, 1.25 V. The multimeter agrees, and this instant agreement between position, arithmetic, and measurement is exactly what makes the divider the right second circuit for a classroom.

Loading: the part everyone learns the hard way

A divider only holds its voltage if nothing heavy hangs off it. Prove it: set the pot to 50% (2.50 V), then wire a 10 kΩ resistor from the wiper to ground and watch the reading fall. The pot is 10 kΩ end to end, so the wiper now sees its lower 5 kΩ in parallel with your 10 kΩ, and the output sags to 2.00 V. Make the load 1 kΩ instead and it collapses to about 0.7 V.

That sag is not an error, it is the lesson: a divider is a reference, not a power supply. If the number matters, the thing reading it should be high-impedance, which is why the next stage after a divider is so often an op-amp follower or an ADC pin. Remove the load and the 2.50 V comes back, no harm done.

Linear vs audio taper, measured

Real pots come in tapers, and so does the simulated one. On the pot's Position card, switch the taper between Linear and Audio (log), and repeat the slow sweep while watching the trace:

• Linear: voltage tracks position evenly; 50% of travel is 50% of voltage.
• Audio: the first half of the travel moves the voltage only a little, then the second half does most of the work. At 50% position the output sits well below 2.5 V.

The audio taper exists because human loudness perception is logarithmic; a linear pot on a volume control spends half its travel between "loud" and "slightly louder". Being able to flip between tapers on one part and watch the same sweep produce two different curves is the fastest explanation of the concept we know.

A trimmer is a pot that has decided

The Trimmer next to the pot in the palette is the same electrical part in set-and-forget form: you adjust it while building, then leave it. Use the pot for anything the user of the circuit touches, the trimmer for calibration. Both appear under Inputs while you browse, since that is what they usually are.

Next week the divider grows up: a potentiometer wired to the RP2040's ADC, with MicroPython turning knob position into LED brightness. If you want the deeper reference meanwhile, the part's behaviour and taper model live at docs.devoltapp.com/parts/passives.