Session 21: Hardware fault finding with meter and scope
Learning outcomes
- Apply the power, then signal, then software fault sequence
- Predict and measure rail voltages and pin levels on a running Uno
- Find broken jumpers and split rails with continuity mode
- Prove a subsystem with a minimal test sketch
Kit and components
- Uno, breadboard, LED and 330 Ω resistor, push button, jumpers
- Multimeter and oscilloscope
- Six prepared fault stations, each bench with one hardware fault
Pre-reading about 25 min
Students read these on their phones before class. They are listed on the student Before class page.
Session plan
- 0:0010 minRecap
Code-correction reflections
Share the most common inventory mistakes from S20 without naming learners.
- 0:1020 minDemo
Power, signal, software
Follow the fault-finding sequence on a bench with a dead LED: rails first, then the pin, then the sketch.
- 0:3050 minStations
Fault stations
Six benches, one fault each: split rail, reversed LED, broken jumper, missing GND, wrong pin, button across the wrong rows. Pairs rotate every 8 minutes and log symptom, measurement, cause and fix.
- 1:2025 minMeasure
Predict, then measure
Students predict and then measure D2 with the button open and pressed, the 5 V and 3.3 V rails, and a PWM pin on meter and scope, recording expected against measured.
- 1:4515 minWrap-up
Which measurement found it fastest?
Checkpoint: ready to move on?
Each pair has logged at least five station faults, with the measurement that identified each one.
Extension for fast finishers
Write a minimal test sketch that checks every pin in their circuit and prints a pass or fail line for each.
Catch-up path
Pair with a student who has passed; concentrate on the first three steps of the sequence - observe, power off, inspect.
Homework and practice
Pre-reading for S22.
Facilitator notes
- Set up and label the fault stations before the session, and keep a key of the faults.
- Flex session: in a shorter course, show the sequence in the S19 demo and use two stations only.