Multi-Zone Reaction Trainer

A reflex-training device that tests more than just how fast you react — it tests whether you react in the right place. Four ultrasonic sensors, mounted in a fixed row, each watch their own zone; a laptop dashboard picks one at random each round, times your response, and automatically corrects for the communication link's own delay so that delay is never mistaken for part of your reflex.

Built for VIKRAMA 2026 — a Science Modelling Competition organized by Akhil Bharatiya Vidyarthi Parishad (ABVP), Mangaluru, in association with Canara Educational Institutions, held at Canara Vikaas PU College, Mangaluru, to commemorate the birth anniversary of Vikram Sarabhai.

Why spatial reaction, not just speed

Most simple reaction testers measure one thing: a light turns on, you press a button, the system times it. That tests speed alone. Real reactions are rarely that simple — reacting quickly in the wrong direction is still a failure. This project splits the test surface into four independent zones, so a correct response has to be both fast and in the right place.

How it works

• Four ultrasonic sensors (HC-SR04) sit in a fixed horizontal row, 15 cm apart — Zone 1 through Zone 4, left to right.
• An Arduino Uno continuously reads all four sensors and streams their live distances over a serial link. It has no awareness of rounds, scoring, or difficulty — its only job is sensing and communication.
• A browser dashboard (dashboard/index.html) owns all of the game logic: picking the target zone, timing the round, checking whether the correct zone responded, scoring, and keeping session history — all running client-side, no server required.
• Automatic latency calibration. The moment the dashboard connects, it sends a timestamped ping over the link and the Arduino echoes it back immediately. The measured round-trip time is used to correct every reaction-time reading for that session, so the link's own transmission delay is never counted as part of the user's reflex. For full test methodology and empirical 100-cycle jitter data, see the Latency Calibration Benchmark Report.

Ultrasonic Sensors → Arduino Uno → Serial Link → Dashboard
                                        (game logic runs entirely here)

Serial Transports & Baud Rates

The firmware supports two communication interfaces:

• Primary Verified Configuration — Direct USB Serial @ 115,200 baud: The official configuration used during the VIKRAMA 2026 live competition demonstration and documented in the latency benchmarks. High throughput with minimal packet serialization delay (Serial.begin(115200)).
• Wireless Bluetooth — HC-05 Module @ 9,600 baud: Operates via Arduino SoftwareSerial on pins 10 (TX) and 11 (RX) at 9,600 baud (bluetoothSerial.begin(9600)).

In the web dashboard, use the Transport toggle above the connect button:

• USB (115200) opens the Web Serial port at 115,200 baud.
• HC-05 BT (9600) opens the paired Bluetooth COM port at 9,600 baud.

Once connected, the 8-sample latency calibration handshake automatically measures round-trip time and estimates one-way link transit delay for whichever transport is selected.

Engineering context: The Bluetooth path was part of the original design, but the specific HC-05 clone module proved erratic close to the competition deadline. The build actually demonstrated ran over direct USB serial. Both paths are fully implemented in firmware and supported by the dashboard transport selector.

Acoustic Isolation & Trigger Architecture

• Competition Build (Shared TRIG on D2): In the original VIKRAMA 2026 build, all four sensor TRIG pins were joined to Arduino pin D2 without a breadboard to reduce wire harness weight and bulk. To prevent acoustic reflections from overlapping across zones, the firmware enforces a 60 ms inter-zone settling pause (triggerSettleMillis = 60UL) between zone measurements. At standard sound speed (~343 m/s), 60 ms allows sonic waves to travel >20 meters and dissipate before the subsequent sensor is triggered.
• Independent Trigger Configuration (INDEPENDENT_TRIG_PINS 1): For environments with heavy reflective acoustic boundaries or tight enclosures, set #define INDEPENDENT_TRIG_PINS 1 in ReactionTrainer.ino and wire Zone 1–4 TRIG lines to pins D2, D7, D8, D9. This completely isolates ultrasonic bursts to only the active zone being polled.

Hardware

Component	Notes
Arduino Uno	Central controller
Ultrasonic sensor (HC-SR04) × 4	Mounted in a row, 15 cm apart
HC-05 Bluetooth module	Optional — USB works without it
Jumper wires (male-to-female)	See wiring below
9V battery + Uno barrel connector	Power

No breadboard is required for the competition build — see the wiring notes below for how the shared sensor lines are joined.

Wiring (Competition Build)

Connect	To
All 4 sensors' TRIG (tied together)	Arduino D2 (or D2, D7, D8, D9 if INDEPENDENT_TRIG_PINS enabled)
Zone 1 sensor ECHO	Arduino D3
Zone 2 sensor ECHO	Arduino D4
Zone 3 sensor ECHO	Arduino D5
Zone 4 sensor ECHO	Arduino D6
HC-05 TXD	Arduino D10
HC-05 RXD	Arduino D11
All 4 sensors' VCC (daisy-chained)	Arduino 5V
All 4 sensors' GND (daisy-chained)	Arduino GND
HC-05 VCC / GND	Arduino 5V / GND

No breadboard, no problem: since a shared line (TRIG, 5V, GND) would need more than one wire in a single Arduino pin header hole, twist the bare male ends of several male-to-female jumpers together by hand, then plug one more male-to-female wire's female end over that twisted bundle back to the Arduino pin. Wrap the joint in tape. Three such junctions cover TRIG, VCC, and GND — every other connection (each ECHO pin, the HC-05 lines) is a normal one-wire connection.

Physical order matters: whichever sensor is wired to D3 should be your physical leftmost sensor, then D4/D5/D6 moving right, so the on-screen zone numbering matches the physical layout.

HC-05's RX line is not always 5 V-tolerant — check your specific module's datasheet before wiring it directly; some breakout boards include their own level-shifting, others don't.

Setup

1. Open firmware/ReactionTrainer/ReactionTrainer.ino in the Arduino IDE and upload it to an Arduino Uno.
2. Open dashboard/index.html directly in Chrome or Edge (Web Serial API support is required — Firefox and Safari won't work).
3. Click Connect and select the Arduino's port from the picker — either its direct USB serial port, or the HC-05's paired Bluetooth COM port if you've paired it in your OS Bluetooth settings first.
4. Wait for calibration to finish (a handful of round-trip pings — a couple of seconds), then choose a difficulty and mode and hit Start Session.

The dashboard's diagnostics strip shows live raw distance readings from all four zones at all times — useful for confirming wiring, and for tuning the trigger threshold (TRIGGER_THRESHOLD_CM near the top of the dashboard's script, default 8 cm) to match your actual sensor mounting.

Troubleshooting

If a serial connection opens but calibration never completes ("Calibration ping timed out"), the fastest way to see what's actually happening is over USB, independent of Bluetooth entirely:

1. Set VERBOSE_SERIAL_DEBUG to 1 near the top of the .ino file and re-upload.
2. Open the Arduino IDE's Serial Monitor at 115200 baud.
3. Watch what arrives while attempting to connect over Bluetooth from the dashboard: silence means nothing is reaching the Arduino at all (check wiring); garbled bracketed byte values mean a baud-rate mismatch between the Arduino and the HC-05; clean readable PING: text means the Arduino side is working correctly and the issue is elsewhere in the link.

License

MIT — see LICENSE.

Team

Built by Shreesha Rao K — SDM School, Mangalore — for VIKRAMA 2026.