Wilteq WILTEQArduino Self-Study
Week 8 · Sensors & Task B

Session 36: Resistive sensors and the LDR

Teach & build120 minLesson 23: Resistive Sensors, Dividers & the LDR

Learning outcomes

  • Wire an LDR divider in the course order
  • Calculate sensor resistance from an ADC count and check it with a multimeter
  • Choose a fixed resistor for sensitivity at a chosen light level
  • Switch an output with hysteresis

Kit and components

  • Uno, LDR, 1 kΩ, 10 kΩ and 100 kΩ resistors, LED and 330 Ω resistor, breadboard
  • Multimeter and oscilloscope

Pre-reading about 25 min

Students read these on their phones before class. They are listed on the student Before class page.

  1. Lesson 23: Why resistive sensors need a voltage divider
  2. Lesson 23: Divider calculation (course wiring)
  3. Lesson 23: Thresholds and hysteresis
  4. Theory Reference: Hysteresis (two thresholds)

Session plan

  1. 0:0010 min
    Recap

    Quiz: formatting

  2. 0:1020 min
    Demo

    Resistance to voltage to count

    Cover and uncover the LDR while Serial shows counts and resistance; swap the fixed resistor and show how sensitivity changes.

  3. 0:3030 min
    Measure

    Calibration logger

    Students run the calibration logger, record counts and resistance covered, in room light and under a lamp, and check one resistance with the meter (power off).

  4. 1:0035 min
    Build

    Night light with hysteresis

    Students choose darkOn and brightOff from their own table and show no flicker at the boundary.

  5. 1:3525 min

Checkpoint: ready to move on?

Students' night light switches cleanly using thresholds chosen from their own measurements, recorded in the logbook.

Extension for fast finishers

Start-up threshold calibration (lesson challenge).

Catch-up path

Use the lesson's thresholds unchanged, then adjust them once.

Homework and practice

Draft Task B success criteria and a calibration plan.

Facilitator notes

  • Under mains lighting the scope may show 100 Hz ripple on the divider - a good discussion of why readings wobble.
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