Brain Bots

30 minmedium

MISSION 16 · INTERMEDIATE ARDUINO

Two-Eye Light Compass

Make two-eye light compass. Explore compare two calibrated inputs.

Public beta missionThese revised instructions are open for learning while actual-kit testing is pending. A grown-up must confirm every setup check before power is connected. If a rating, pin card or required check is missing, explore the idea on screen and leave the physical build unpowered.

2 · Light Explorers

Your new skill: Compare two calibrated inputs

Revisit the skill you will reuse: shadow stopwatch

WHAT YOU'LL USE

Match these to your kit

Arduino UnoUSB A-to-B data cableHalf-size breadboardMale–male / male–female jumper wires (as needed for actual module terminals)2 LDRs, 2 × 2.7 kΩ, 2 LEDs, 2 × 2.2 kΩ

Gather from home

Computer with Arduino IDE and Serial MonitorPaperPencil

Reuse the parts between missions; these are not 45 simultaneous installations. Red/yellow/green means those three monochrome colours. RGB is a separate component with three channels.

BEFORE YOU BUILD

Unplug USB before changing connections. Use only the USB supply for this build; never connect 9V to 5V or a signal pin, and never connect to mains. An adult verifies variant, printed pin labels and resistor values before powering. Stop and unplug if a part becomes hot or damaged.

YOUR REWARD

+30 XPMission completion

PREDICT BEFORE YOU BEGIN

Before the test: which input will change, and what signal or reading do you expect?

BEFORE YOU BUILD

Parent check: exact part variant, labelled pins and stated values. If a check cannot be confirmed, keep this physical build unpowered and explore the code and prediction instead.

YOUR CHALLENGE

Build two-eye light compass and prove its rule.

NEW POWER-UP

Compare two calibrated inputs

You have explored time between threshold events. Now try compare two calibrated inputs.

Adult help: Adult helps with computer setup, first wiring and any water/cutting. Learner predicts, tests and explains.

See the idea before you build

How a breadboard connects inside

Each coloured strip is one connected group. Different numbered rows stay separate. This explains the board; use the mission’s exact connection reference for component positions. Check rail breaks on your supplied board.

ldr divider learning diagram — See the idea, then follow this mission’s exact pin-to-pin map below. · Tap to enlarge

Exact labelled connections for Two-Eye Light Compass — Pin-to-pin reference for this sketch. Match printed labels and actual component variant. · Tap to enlarge

Open the complete Arduino code

Copy the complete code into Arduino IDE or download the sketch. Follow the matching component card before connecting power.

// First Wonder Brain Bots 16 — Two-Eye Light Compass
// USB-powered model. Unplug before rewiring. Serial Monitor: 9600 baud.
unsigned long lastReport=0;
int leftOffset=0;
int rightOffset=0;
int deadband=80;

void setup(){Serial.begin(9600);pinMode(8,OUTPUT);digitalWrite(8,LOW);pinMode(12,OUTPUT);digitalWrite(12,LOW);Serial.println("Ready. Follow your mission test.");}
void loop(){
  unsigned long now=millis();
  
int left=analogRead(A0)-leftOffset,right=analogRead(A1)-rightOffset;
int difference=left-right;digitalWrite(8,difference>deadband);digitalWrite(12,difference<-deadband);
if(now-lastReport>=500){lastReport=now;Serial.println(abs(difference)<=deadband?"NEUTRAL":difference>0?"LEFT BRIGHTER":"RIGHT BRIGHTER");}
}

Check the connection map

CONNECTION MAP

Build the electrical path before you test.

Keep power disconnected while changing connections.

JoinConnectWhy it matters

PowerSupplied USB data cable → Uno USB socket; computer at other endThe same cable uploads and supplies this model. Unplug before wiring.

Shared referenceUno GND → breadboard ground railAll module GND terminals use this same reference. Check whether your rail is split.

LED cue 1D8 → 2.2 kΩ → LED anode (+); cathode (−) → GNDUse separate breadboard strips. Short leg/flat rim usually marks cathode; verify.

LED cue 2D12 → 2.2 kΩ → LED anode (+); cathode (−) → GNDUse separate breadboard strips. Short leg/flat rim usually marks cathode; verify.

LDR 15V → LDR → junction → 2.7 kΩ → GND; junction → A0This divider normally reads higher in brighter light. Calibrate the actual part.

LDR 25V → LDR → junction → 2.7 kΩ → GND; junction → A1This divider normally reads higher in brighter light. Calibrate the actual part.

Kit variant and values confirmed by an adult

All pins match the map; USB was disconnected while wiring

Test includes expected, non-triggering and recovery cases

BUILD PATH

STEP 1 OF 6

Meet your mission

Try · Notice · ExplainRead the checkpoint, make a prediction, then test your idea.

You will explore compare two calibrated inputs. Gather the kit and home materials below. Unplug USB. Match the part names and printed labels.

Watch this step

A video demonstration will appear here when it is ready. You can follow the written step now.

Read the video instructions

You will explore compare two calibrated inputs. Gather the kit and home materials below. Unplug USB. Match the part names and printed labels.

Need a diagram for this step?

WHAT'S REALLY HAPPENING?

Why it works

Compare two calibrated inputs. Raw light readings depend on this divider and your room. They are not calibrated lux. Check your rule against an example where it should respond and one where it should not. Small differences need not count as a clear direction.

This is a tabletop learning model. Controllers reuse inputs, decisions and outputs to automate a useful signal.

FAIR-TEST CHALLENGE

Change one input or setting at a time; keep the wiring and protection unchanged. Repeat three trials.

WHEN IT DOESN'T WORK YET

Debug one clue at a time.

Upload or port missing

Likely cause: Wrong board, port or cable connection

Try this first: Check Arduino Uno selection and supplied data cable. Unplug external wiring before checking upload on built-in LED.

Signal does not match the test

Likely cause: Pin labels, input calibration or variant differs

Try this first: Unplug. Compare every connection with the map. Return to the earlier single-input mission; test one subsystem at a time.

Reading is unknown or unstable

Likely cause: Sensor settling, target, contact or calibration

Try this first: Follow the exact test setup; allow settling, use a flat target or check module pinout unpowered. Never replace unknown with a guessed safe reading.

CLEAN, RESET AND STORE

Disconnect USB, remove wires carefully and store components dry.

NEXT SKILL

AND and OR