Automatic door or barrier
How does a controller turn presence and position signals into motion while making obstruction the dominant condition?
An automatic barrier combines an actuator and linkage with state logic. A request may start opening, position feedback marks travel limits, dwell timing holds the opening, and a close command is permitted only while presence/obstruction conditions remain clear. Energy and information travel on different paths: actuator power creates torque, while low-energy signals decide when it is allowed. The paper analogue explores that priority logic only; it is lightweight, slow, and explicitly not safety-rated.
Follow the flows
Energy makes change possible. Information selects, sequences, and corrects that change.
Energy
- Low-voltage bench supply
- Servo electronics and motor
- Output shaft torque
- Paper linkage
- Lightweight barrier motion plus heat/sound
Information
- Request/presence/obstruction input
- Priority state machine
- Bounded servo position command
- Paper barrier motion
- Simulated endpoint/clear state feedback
Subsystem map
Observe externally first; documentation fills in what the enclosure deliberately hides.
Presence, request, and obstruction inputs
Report that opening is requested or that closing must stop/reverse.
- Energy or signal
- Button/sensor state → controller input with defined active and fault meanings.
- Observe
- From outside a real installation, note approach, open, dwell, and close timing without blocking, touching, or deliberately defeating sensors.
State controller
Prioritize obstruction, sequence closed/opening/open/closing states, and handle timeouts.
- Energy or signal
- Input state + timer + position → bounded motion command or safe stop.
- Observe
- Build a timing diagram from normal public operation and documentation; unknown behavior stays unknown.
Motor/servo and power path
Convert controlled electrical power into bounded rotation.
- Energy or signal
- Electrical power + position command → shaft torque, motion, heat, and sound.
- Observe
- On the analogue, listen for stall/buzz and disconnect immediately; never force a real powered barrier.
Linkage, barrier, and position limits
Transform shaft rotation into useful barrier motion and report endpoints.
- Energy or signal
- Shaft torque → linkage force → barrier angle/translation; endpoint signal returns to controller.
- Observe
- Measure the paper linkage geometry and commanded endpoints with power off before a slow powered test.
Test the idea safely
Proposed, unvalidated bench exercise: a slow SG92R moves a weak paper barrier while buttons simulate request and obstruction inputs. It is a state-priority demonstrator—not a door, gate, safety-rated barrier, household-equivalent product, or completed BOM.
Goal
Test state priorities and bounded motion on a slow, lightweight paper barrier.
Procedure
- With power disconnected, make a weak paper linkage and set mechanical endpoints that cannot trap a finger or load the servo near stall.
- Draw closed, opening, open, closing, and stopped/fault states; make obstruction override closing before writing commands.
- Verify connector order, shared reference as documented, servo supply capacity, signal limits, and accessible disconnect.
- Test initially with the servo horn disconnected, then attach the paper linkage and command only slow bounded movement while the area stays clear.
- Press the simulated obstruction button during closing and confirm the observed state and command match the prediction; disconnect on buzz, binding, or unexpected motion.
Observe
- State and commanded angle
- Paper barrier endpoint
- Response latency to the simulated obstruction
- Binding, overshoot, buzz, or reset
Diagnose
- Reset during motion: disconnect power and review servo current path, wiring, and supply capacity.
- Wrong direction: remove the horn with power off, correct state/angle mapping, and re-establish safe endpoints.
- Obstruction ignored: stop testing until input polarity, priority ordering, and transition coverage are corrected.
Limits
- Use only a weak paper/lightweight barrier with no pinch or impact hazard; this is not safety-rated.
- Do not connect to, modify, or test on a real door, gate, garage opener, access system, or fire/smoke barrier.
- The exercise does not validate entrapment protection, redundant sensing, structural loads, compliance, or a deployable product.
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.
- Confirm the actual servo label, connector order, travel, horn fit, load, and current demand before connecting it.
- A controller signal pin is not a servo power source; choose and validate the power path separately.