A light sensor by division
The voltage divider is the first circuit you've learned that computes something: it turns a resistance into a voltage. Pair it with a resistor that responds to the world — a light-dependent resistor — and you have a sensor. In this capstone you design the divider on paper, predict its output in light and dark, and then build it as a real board whose rules engine enforces the very constraint you learned in Lesson 3: dividers feed ADC pins.
- On paper: an LDR (≈5 kΩ in bright light, ≈100 kΩ in darkness) sits on top of a divider from the 3.3 V rail, with a 10 kΩ fixed resistor on the bottom. Compute the output voltage in bright light and in darkness, and confirm both fall inside the Pico ADC's 0–3.3 V range.
- Compute the divider's worst-case power draw (bright light, smallest total resistance) and satisfy yourself it is negligible for a battery-powered board.
- Open PCB Studio, add the Pico 2 W and the LDR divider part, and note which pins the pin dropdown offers you. Connect it, then also add a potentiometer — a second divider, this one adjustable.
- Try to defeat the rules engine: hand-edit the spec JSON to move the potentiometer to a non-ADC GPIO and generate. Read the validation error you get — that error is Lesson 3's loading/ADC discussion enforced in code.
- Restore a legal pin, generate the schematic, then run "Generate + PCB layout" and download the Gerber zip. You have now designed, validated, and exported a manufacturable light-sensing board from first principles.