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Arduino prints Serial.print(temperature); Serial.print(","); Serial.println(humidity); with temperature = 22.4 and humidity = 48. Write the exact characters that travel over USB, including the invisible ones.
println adds a newline (\n). There is no space after the comma.22.40,48.00 followed by \n. (Arduino may print extra zeros — the important part is number,comma,number,newline.)A classmate uses a bare 3-pin DHT11 with only three wires: 5V, GND, DATA. Readings fail at random. Explain, in 4–6 sentences, what a pull-up resistor does on the DATA line and why the module version often works without an extra resistor.
Processing window is 640 px wide. You draw a bar starting at x = 40, and you want 50 °C to fill 520 px. What is map(28, 0, 50, 0, 520)? How wide is the bar at 28 °C?
This sketch sometimes prints nan,nan and Processing’s bars vanish. Find two bugs and write the corrected loop().
void loop() {
float h = dht.readHumidity();
float t = dht.readTemperature();
Serial.print(t);
Serial.print(",");
Serial.println(h);
delay(200);
}isnan() guard. Bug 2: 200 ms is too fast. Guard and wait 2 s.void loop() {
float h = dht.readHumidity();
float t = dht.readTemperature();
if (isnan(h) || isnan(t)) {
Serial.println("Failed to read from DHT sensor!");
delay(2000);
return;
}
Serial.print(t);
Serial.print(",");
Serial.println(h);
delay(2000);
}Extend the dashboard so every accepted reading is appended to climate.csv as millis,temp,hum. Create the file in setup() with a header row.
PrintWriter log = createWriter("climate.csv"); then log.println(...) and log.flush().setup(), write a header, then in serialEvent after a successful parse write millis()+","+temperature+","+humidity and flush().PrintWriter log;
void setup() {
// ... serial setup ...
log = createWriter("climate.csv");
log.println("millis,temp,hum");
}
void serialEvent(Serial p) {
String data = trim(p.readStringUntil('\\n'));
String[] v = split(data, ",");
if (v.length != 2) return;
temperature = float(v[0]);
humidity = float(v[1]);
log.println(millis() + "," + temperature + "," + humidity);
log.flush();
}Design (on paper or in code) a 2-minute scrolling chart of temperature. List: the data structure you store, how many points, how you map time to x and temperature to y, and what happens when the array is full.
append() + subset() to drop the oldest point.for i in 0..n-2: a[i]=a[i+1]) and write the new sample at the end. Draw with beginShape() / vertex() / endShape().Wiring: LDR to 5 V, 10 kΩ to GND, tap to A0. You cover the LDR with your palm. Does analogRead go up or down? Explain in two sentences.
R_LDR = 4 kΩ, R_fixed = 10 kΩ, V_in = 5.0 V. Compute V_A0 and the expected analogRead (round to nearest integer).
Arduino’s ADC is 10-bit, 0–5 V. How many millivolts is one analogRead step? If the reading jumps from 400 to 401, how much did the voltage change?
Processing shows “Light intensity: 0” forever. The Serial Monitor (when Processing is closed) shows numbers. Find the bug.
void draw() {
if (myPort.available() > 0) {
String val = myPort.readStringUntil('\\n');
lightLevel = int(val);
}
}int(null) and leftover \r will fail. Also, reading in draw can catch half a line.readStringUntil can return null. Windows often sends \r\n, so int("412\r") is 0. Trim and guard. Prefer serialEvent.void serialEvent(Serial p) {
String val = p.readStringUntil('\\n');
if (val == null) return;
val = trim(val);
if (val.matches("\\\\d+")) lightLevel = int(val);
}Add an LED on D8 (220 Ω to GND). Turn it on when lightValue < 350 and off otherwise. Keep sending the reading to Processing.
pinMode(8, OUTPUT); in setup. digitalWrite(8, lightValue < 350 ? HIGH : LOW);const int sensorPin = A0;
const int ledPin = 8;
const int DARK = 350;
void setup() {
Serial.begin(9600);
pinMode(ledPin, OUTPUT);
}
void loop() {
int lightValue = analogRead(sensorPin);
digitalWrite(ledPin, lightValue < DARK ? HIGH : LOW);
Serial.println(lightValue);
delay(200);
}You cannot trust 0–1023 as “percent brightness”. Write a 6-step procedure to calibrate your kit: record dark-desk, room, and window-sill readings, then decide how Processing should map those three numbers onto a 0–100 % scale.
dark. 2. Point at the ceiling lights → room. 3. Hold at the window → bright. 4. In Processing, pct = constrain(map(lightLevel, dark, bright, 0, 100), 0, 100). 5. Label the bar with those three marks. 6. Recalibrate if you change the 10 kΩ or the room.pulseIn returns 2915 µs. Using 343 m/s, how far is the object in centimetres?
The code assumes 343 m/s. The room is 10 °C (v ≈ 337.4 m/s). A wall is truly 100 cm away. What distance does the sketch print, and what is the % error?
A student used the original blocking sweep. Explain in 4 sentences why STOP waits, then write the non-blocking idea in two lines of pseudocode.
for (angle = 0; angle <= 180; angle++) { servo.write(angle); delay(10); } does not call Serial.available() for 1.8 s. The STOP line sits in the UART buffer. Pseudocode: each loop: read serial → update sweeping flag → if sweeping, angle += dir, write once, delay 12 ms.Arduino prints distance: 42.0 cm. Write serialEvent that extracts 42.0. Do not crash on distance: 0.0 cm or a timeout line.
splitTokens(data, " :cm") or find the first number with a small scan.void serialEvent(Serial p) {
String data = trim(p.readStringUntil('\\n'));
String[] bits = splitTokens(data, " :cm");
for (int i = 0; i < bits.length; i++) {
if (bits[i].length() > 0 && Character.isDigit(bits[i].charAt(0))) {
distance = float(bits[i]);
break;
}
}
}Window 600×600, origin at (300, 580). Angle 45°, distance 50 cm mapped onto r = 0…250 for 0…100 cm. Compute x and y of the blip.
Design a Processing UI for a reversing sensor: three zones (<30, 30–80, >80 cm), colour, optional beep, and a frozen “HOLD” button that stops the servo. Sketch the layout and list the serial messages in both directions.
angle,distance or just distance. PC → Arduino: START, STOP, maybe HOLD. UI: big number, coloured bar, zone chips, mute toggle. Beep interval shortens as distance falls (map 80→30 cm onto 800→80 ms). HOLD sends STOP and freezes the last bar.R_known = 1000 Ω, V_A0 = 2.0 V, V_in = 5.0 V, unknown on the 5 V side. Find R_x.
R_x = 2.2 kΩ, R_known = 1.0 kΩ, unknown on 5 V side. Compute V_A0 and analogRead.
In 5–6 sentences, explain why a 1 kΩ reference is a bad choice for a 1 MΩ unknown. Mention V_A0 and one ADC step (≈ 4.9 mV).
Someone unplugged the unknown resistor. Processing prints Infinity Ω. Point to the line that blew up and write the guard.
float Vout = (raw * 5.0) / 1023.0;
float Rx = 1000.0 * (5.0 / Vout - 1.0);
Serial.println(Rx);5.0 / Vout is infinity. Send a sentinel (−1) and let Processing print OPEN.if (raw < 2) { Serial.println(-1); return; }
float Vout = (raw * 5.0) / 1023.0;
Serial.println(1000.0 * (5.0 / Vout - 1.0));Processing keys 1, 2, 3 send "K,1000\n", "K,10000\n", "K,100000\n". Arduino updates Rknown when a line starts with K. Keep printing R_x as a number.
Serial.readStringUntil and startsWith("K,"). On Processing keyPressed().float Rknown = 1000. Each loop, if serial is available, read a line; if it starts with K,, parse the rest as the new known value. Processing’s keyPressed writes the matching command.You dip a typical classroom probe from dry potting mix into a wet cup. Does analogRead rise or fall? Why did the Processing bar still get longer in the starter sketch?
map(moisture, DRY, WET, 0, 100) has DRY > WET, so a smaller input maps to a larger output. The bar follows wetness, not voltage.Your calibration: DRY = 880, WET = 340. A reading is 610. What % wet is constrain(map(610, 880, 340, 0, 100), 0, 100)?
Fill in a table: medium (dry soil, damp soil, wet soil, cup of water, open air) × 10 readings × average. Then choose DRY and WET for your Processing sketch. Photograph the table or type it into the handbook.
Average the last 8 analog readings on Arduino before printing. Keep the serial contract as one integer per line.
const int N = 8;
int buf[N];
int i = 0;
void loop() {
buf[i] = analogRead(A0);
i = (i + 1) % N;
long sum = 0;
for (int k = 0; k < N; k++) sum += buf[k];
Serial.println(sum / N);
delay(50);
}A single threshold if (reading > 700) pumpOn(); else pumpOff(); will flip the relay every few hundred milliseconds as the reading hovers. Design hysteresis: pick two numbers and write the if logic. Explain why plants (and relays) prefer this.