Ion4 Smart Crossing
The crossing
People crossing
Environment
Live map
Where people are around the crossing, live. A person inside the crossing zone while the robots show blue (cars go), or on the railway while a train is coming, is logged as an infraction. Free map (OpenStreetMap), no API key. Locations are shared only when a person presses "Share my location".
Zones
People now 0
Infractions 0
Controls
Gates move from here only through the hardware tests below, which run in maintenance mode and are refused while a train is on the crossing. A remote command can never lift a barrier onto a train.
Event log
Ask the crossing
AI assistant (Gemini 3.8 Flash). It sees the live crossing data with every question.
Email alerts
- Fire or gas emergency at the crossing
- Flooded path or ice risk on the road
- Train on the crossing for more than 60 s
- Device offline for more than 60 s
Each alert type sends at most once every 10 minutes. Alerts go out from this page, so keep it open on one laptop during the demo. Preview data never sends email.
Hardware test
Robots (both lanes)
Lights
Buzzer
Railway gate
Car barrier
Whole crossing
Each test lasts 3 seconds (the up-and-down tests and the train drill 6 s). Gates moved by a test go back to automatic after 30 seconds. Device reply: --
Boot self-test
| Part | Result | Detail |
|---|---|---|
| Reset the ESP32, or press "Run self-test again" in maintenance mode. | ||
Inputs: check each one on the real device
| Part | Reading now | How to check it | Result |
|---|---|---|---|
| DS18B20 temperature | -- | Hold the probe in your hand, it should rise | -- |
| MQ-5 gas | -- | Unlit lighter gas near it, the value jumps | -- |
| Soil moisture | -- | Dip the probe in water, it rises | -- |
| LDR light | -- | Cover it with your hand, it drops | -- |
| Ultrasonic 1 (train) | -- | Hand in front, distance changes; under 10 cm = train | -- |
| Button 1 pedestrian | -- | Press it on the device | -- |
| Button 2 railway gate | -- | Press it on the device | -- |
| Button 3 car barrier | -- | Press it on the device | -- |
| Button 4 street lamp | -- | Press it on the device | -- |
| WiFi signal | -- | Better than -75 dBm is solid | -- |
| City mainframe link | -- | Needs CITY_HOST in config.h | -- |
Pin connections
ESP32 Dev Board 30-pin (CP2102), labels as printed on the board. Buttons use the internal pull-up: one leg to the pin, the opposite leg to GND. Every LED has its own resistor.
| Pin | Part | Wiring | Extra part |
|---|---|---|---|
| Traffic robots (left and right lane share pins) | |||
| D25 | RED, both robots | D25 → 220Ω → LED → GND, twice | 2 × 220Ω |
| D26 | ORANGE, both robots | D26 → 220Ω → LED → GND, twice | 2 × 220Ω |
| D33 | BLUE, both robots | D33 → 100Ω → LED → GND, twice | 2 × 100Ω |
| Push buttons | |||
| D13 | Button 1, pedestrian | D13 ↔ button ↔ GND | none |
| D18 | Button 2, railway gate | D18 ↔ button ↔ GND | none |
| D19 | Button 3, car barrier (hold 3 s = emergency) | D19 ↔ button ↔ GND | none |
| D21 | Button 4, street lamp (hold 3 s = maintenance) | D21 ↔ button ↔ GND | none |
| Train sensor and gates | |||
| D27 | Ultrasonic 1 TRIG (train) | direct | none |
| VN | Ultrasonic 1 ECHO (train) | ECHO → 1kΩ → VN → 2.2kΩ → GND | 1kΩ + 2.2kΩ |
| RX2 | Servo, car barrier | orange → RX2, red → breadboard 5V rail, brown → GND | none |
| TX2 | Servo, railway gate | orange → TX2, red → breadboard 5V rail, brown → GND | none |
| Environment | |||
| D4 | DS18B20 temperature | yellow → D4, red → 3V3, black → GND, 4.7kΩ D4 to 3V3 | 4.7kΩ |
| D34 | MQ-5 gas | AO → 10kΩ → D34 → 10kΩ → GND, VCC → breadboard 5V rail | 2 × 10kΩ |
| D35 | Soil moisture | AO → D35, VCC → 3V3, GND → GND | none |
| D32 | LDR light sensor | 3V3 → LDR → D32 → 10kΩ → GND | 10kΩ |
| D22 | Street lamp LED | D22 → 220Ω → LED → GND | 220Ω |
| D23 | Buzzer TMB12A03 (active, 3 V) | D23 → 1kΩ → BC548 base; buzzer + → 3V3, buzzer − → collector; emitter → GND | BC548 (or BC547) + 1kΩ |
| D2 | Status LED | onboard, nothing to wire | none |
| Power | |||
| 3V3 | 3.3V rail | DS18B20, soil moisture, LDR, buzzer | |
| 5V rail | Breadboard power supply, jumper on 5V | 9V battery clip → its barrel jack; 5V rail → both servos, MQ-5 VCC, ultrasonic VCC | supply module |
| USB | ESP32 power | laptop USB powers the ESP32; do NOT also link VIN to the 5V rail | |
| GND | Common ground | ESP32 GND → breadboard GND rail: the only wire between the two supplies | |
| VIN | Run without the laptop | unplug USB first, then VIN → breadboard 5V rail | |
| Reserved / free | |||
| D14, VP | Ultrasonic 2 (car), not fitted | TRIG → D14, ECHO → 1kΩ → VP → 2.2kΩ → GND; set USE_CAR_SENSOR true | 1kΩ + 2.2kΩ |
| D5, D12, D15 | Boot pins, left free | do not use | |
Device console
Live log from the ESP32 (the same lines it prints on the Serial Monitor), plus what this website does. Everything is also written to the browser console (F12).
Serial Monitor commands (115200 baud, type a letter then Enter)
About Ion4 Smart Crossing
A safer, smarter level crossing for the Adam Tas Corridor in Stellenbosch, where the R44 and the railway line split communities. One small device runs the robots, the gates and the street light, watches the road conditions, and tells the city how long people wait to cross.
Team Ion4 (team ID qsoju) · Hack the City by Octoco, October 2026 · Challenge: Getting Around, moving people across the divide
The problem
People walking between Kayamandi, the town and the university cross busy roads and the railway with long, unpredictable waits. Planners have little data on where people wait and where they bottleneck.
What the crossing does
- Two robots (left and right lane) run red, red + orange, blue, orange in sync.
- A pedestrian button cuts the cars' blue short, and the wait is measured.
- An ultrasonic sensor sees the train: bell, red robots, railway gate and car barrier down.
- Road temperature (ice, heat, fire), gas and smoke, and flooding are watched all the time.
- The street light turns on by itself at night.
Three modes
- Normal: the robot cycle with the walk chirp.
- Maintenance: flashing orange; hardware tests allowed.
- Emergency: flashing red and a siren, barrier down, railway gate open so people can leave, street light on.
Hardware
ESP32 (30-pin), 6 LEDs on 3 pins, 2 SG90 servos, HC-SR04 ultrasonic, DS18B20, MQ-5, soil moisture probe, LDR, buzzer, 4 push buttons, and a breadboard power supply for the 5 V parts. After every reset the device tests each part for 5 s.
Software and data
Firmware in Arduino C++ on two cores: control on one, WiFi and MQTT on the other. Every 30 s it sends uptime, average wait, road temperature and gas level to the Octoco city mainframe, with an HTTP fallback. Its status is retained, with a last will so the city knows when it goes offline. This website gets the full state over HiveMQ Cloud, with an AI assistant and email alerts.
Why it matters
Every press of the button becomes a data point: where people wait, for how long, and at what time of day. That is the evidence the corridor planners need to place crossings, change timings and make the case for funding.
Cloud broker
| Broker | eeb1e83a06da4b44b7a340bc19cd1e75.s1.eu.hivemq.cloud (HiveMQ Cloud) |
|---|---|
| Device port | 8883 MQTT over TLS |
| Website port | 8884 MQTT over secure WebSocket, path /mqtt |
| State topic | ion4/crossing/state, full JSON every 5 s |
| Command topic | ion4/crossing/cmd, for example {"cmd":"mode","val":"maintenance"}, {"cmd":"test","val":"train_drill"}, {"cmd":"self_test","val":"run"} |
| People topic | ion4/crossing/people, phone positions from the Live map: {"id","name","lat","lng","acc"} |
| Log topic | ion4/crossing/log, one line of text per device event (the Device console page) |
| City mainframe | hack/qsoju/crossing-01/telemetry every 30 s and hack/qsoju/crossing-01/status (retained), on the Octoco broker |