Washing machine
How does a washer coordinate water, drum motion, locks, sensing, and faults into a safe cycle?
A washer is best understood as a state machine coordinating physical subsystems. Requested cycle, door state, water level, temperature, speed, imbalance, and time determine transitions among lock, fill, agitate, drain, and spin. Energy reaches valves, heater (where fitted), pump, and motor through controlled power stages. The analogue stays dry: LEDs represent water states and a cardboard drum represents motion, so no mains, plumbing, wet electronics, or appliance opening is needed.
Follow the flows
Energy makes change possible. Information selects, sequences, and corrects that change.
Energy
- Electrical supply and water pressure
- Controlled valve/pump/motor power
- Water movement and drum torque
- Garment/water motion
- Drain flow, vibration, sound, and heat
Information
- Cycle choice
- Door/level/speed/time inputs
- State machine
- Valve/pump/motor commands
- Observed next state or fault timeout
Subsystem map
Observe externally first; documentation fills in what the enclosure deliberately hides.
Cycle controller
Sequence states, check transition conditions, command outputs, and time out missing responses.
- Energy or signal
- User selection and sensor inputs → state logic → actuator commands and status.
- Observe
- During an ordinary cycle, record visible state indications and elapsed transitions from outside without defeating the lid/door.
Door or lid interlock
Report closure/lock state and constrain hazardous motion or water states.
- Energy or signal
- Position/lock signal enters the controller; controller permits or inhibits later commands.
- Observe
- Observe only documented normal behavior; never bypass the switch or force the lock.
Fill and drain path
Admit, contain, sense, and remove water.
- Energy or signal
- Electrical commands operate valves/pump; water pressure and gravity move fluid; level signal closes the loop.
- Observe
- Listen for ordinary fill/drain phases and watch external indicators and drain outlet only as installation guidance permits.
Drive, drum, and suspension
Apply bounded torque for tumbling and spin while containing loads and managing imbalance.
- Energy or signal
- Electrical → motor torque → belt/direct drive → drum and load motion → heat, vibration, and sound.
- Observe
- Compare slow tumble and spin from outside; note vibration without touching or moving an operating machine.
Fault handling and user feedback
Stop or restrict the cycle when expected signals do not arrive and communicate what needs attention.
- Energy or signal
- Timers and sensor disagreement → fault state → outputs off/safe plus code, light, or tone.
- Observe
- Use documented error descriptions; do not manufacture blocked drains, imbalance, or lock faults on a household machine.
Test the idea safely
Proposed, unvalidated bench exercise: a dry Pico state model with buttons for door/level, LEDs for water and drive states, a hand-turned cardboard drum, and a fault timeout. It is not a washing machine, household-equivalent product, safety controller, or completed BOM.
Goal
Implement and inspect a dry washer state model with explicit guards and a missing-signal timeout.
Procedure
- Draw states for idle, lock, fill, tumble, drain, spin, complete, and fault; label every transition condition before wiring.
- Wire only the low-voltage buttons and LEDs using verified Pico pins and suitable resistors; the hand-turned drum has no powered drive.
- Predict outputs for a normal input sequence, then step through it and record state, inputs, outputs, and elapsed time.
- Repeat while withholding the simulated level signal and confirm the model enters fault after its defined timeout with outputs inactive.
- Open the simulated door input in each non-hazardous dry state and compare behavior with the transition table.
Observe
- State sequence and dwell time
- Whether outputs match the current state
- Response to door input
- Timeout and recovery behavior
Diagnose
- Skipped state: inspect transition guards and button debouncing before changing the diagram.
- State never exits: check the simulated input level and timer update path.
- Unsafe output persists in fault: make the fault state deactivate outputs first, then repeat the dry test.
Limits
- This is a dry state model: LEDs represent water states, and the drum is hand-turned cardboard.
- Do not connect to mains, water valves, pumps, heaters, or an appliance; do not bypass a washer lid/door lock.
- The exercise does not validate appliance safety, load balancing, waterproofing, or a real motor power stage.
Learn and source deliberately
Lessons explain the transferable concepts. Supplier links identify exact candidates; they are not approval, availability, or a completed order.
Start a project plan for this idea →
Prerequisite lessons
Candidate parts — incomplete list
Choose supplies, connectors, mounting and tools before treating this as an order list.
- The sensor starter targets the original non-wireless Pico. Pico H adds fitted headers; confirm its firmware target. Pico W and Pico 2 require a separate firmware/pin review, not a silent substitution.
- Confirm header population, Micro-USB data cable, logic voltage, and power arrangement against the exact board before wiring.