Blink an LED
One second on, one second off, forever. Where everything starts.
led
Examples
Example sketches
Arduino sketches picked from combinations common in real open-source projects. Not a line is changed: simulate as-is, go to a PCB as-is.
53 sketchesNo login
Basics
5 sketchesRead whether a button is pressed
Prints D2's state to the serial monitor as 0 or 1, over and over.
button
Read a knob
Reads the potentiometer on A0 as a number from 0 to 1023.
pot
Fade an LED up and down
analogWrite walks D13's brightness up and back down forever.
led
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Read it as a voltage
Converts the 0–1023 reading into volts and prints that instead.
pot
Digital I/O
9 sketchesTurn an LED on while a button is held
D13 lights only while the button is pressed.
buttonled
Use the built-in pull-up
Reads a button with INPUT_PULLUP and no external resistor — pressed reads 0.
buttonled
Debounce a button
A button bounces on contact; waiting 50 ms turns the noise into one press.
buttonled
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Count button presses
Detects the moment a button goes down, not whether it is down.
buttonled
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Blink without delay()
Times the blink instead of stopping — the shape you need to do two things at once.
led
Play a melody on a buzzer
Pitches and lengths live in arrays and are played in order.
buzzer
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Turn a knob into a pitch
Maps the A0 reading straight onto an audible frequency.
buzzerpot
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A different note per key
Reads several inputs and sounds the note belonging to whichever is pressed.
buzzerpot
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Sound several buzzers in turn
tone() drives one pin at a time; noTone() frees it for the next.
buzzer
Analog
6 sketchesA knob sets the blink rate
The A0 reading is used directly as the delay, so turning it speeds the blink up.
ledpot
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Turn a reading into brightness
Scales 0–1023 down to 0–255 for analogWrite. This is what map() is for.
pot
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Fade with for-loops
Two for-loops walk the brightness up and back — the same result as Fade, written differently.
led
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Smooth a jumpy reading
Averages the last ten samples. Every sensor project meets this problem.
pot
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Calibrate a sensor to its own range
Learns the lowest and highest values it sees in the first five seconds, then scales to those.
ledpot
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Draw a bar graph with ten LEDs
The higher the reading, the more LEDs light. The simplest way to see a number.
ledpot
Control flow
6 sketches🔒
Light up past a threshold
The LED comes on only when the reading crosses a number you chose. if in its simplest form.
ledpot
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Light several in sequence
A for-loop runs along a row of LEDs and back. This is what loops are for.
led
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Keep going while a button is held
Stays inside the while-loop for as long as the button is down.
buttonledpot
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Branch on a value
Splits a reading into ranges and does something different in each — tidier than a stack of ifs.
pot
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React to a letter you type
Sending a–e over serial lights the matching LED.
led
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Keep pin numbers in an array
Lists the LED pins once and walks the list, instead of naming each pin by hand.
led
Projects
13 sketches🔒
A pull-up button and an LED
D13 lights up while the button is held. Start here.
buttonled
Knob turns a servo
Turn the potentiometer and the servo horn follows it to the same angle.
potservo
Night light
The darker the light sensor reads, the brighter the LED — the brightness is an analogWrite duty cycle.
ldrled
Motion lamp
A PIR sensor lights the lamp and holds it on for three seconds after the last movement.
hc_sr501led
Parking sensor
An ultrasonic range finder beeps at shorter intervals as something gets closer, and lights an LED inside 30 cm.
buzzerhc_sr04led
Button counter
Every press adds one, shown on a four-digit seven-segment display.
buttontm1637
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A doorbell that rings when pressed
Pressing the button turns the NeoPixel ring blue and plays two tones.
buttonbuzzerws2812b
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Measure temperature, humidity, pressure
A BME280 prints to serial and an OLED every two seconds.
bme280_i2cssd1306_i2c
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A knob opens and closes a vent
The servo follows the potentiometer; DHT22 humidity goes to the LCD.
dht22lcd1602_i2cpotservo
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A remote changes fan speed
The IR remote's +/- drives a 12 V fan; it halves itself when the room goes dark.
ir_vs1838bldrload_mosfet
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A clock that wakes when someone walks up
The DS3231's time shows on a 4-digit display, but only while the PIR sees someone.
ds3231_i2chc_sr501tm1637
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Log motion to an SD card
Accelerometer samples stream into motion.csv on a microSD; the LED blinks while logging.
ledmicrosd_spimpu6050_i2c
A greenhouse controller
The relay closes when the DS18B20 passes 28 °C; an ultrasonic sensor measures distance too.
buttonds18b20hc_sr04ledrelay_1chssd1306_i2c
Strings
14 sketches14 String-class sketches with no circuit — serial output only
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Different ways to hold text
Prints each way of constructing a String, one after another.
pot
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Join text together
Adds numbers and text with + to build one sentence.
pot
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Append as you go
Uses += to keep adding to the end of a string.
pot
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Count the characters
Measures a string's length and trims the front when it grows.
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Trim the whitespace
Shows how much shorter a string gets once the spaces at each end go.
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Find where something is
Locates a character or word inside a string by position.
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Cut out a piece
Takes just the part of a string you asked for.
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Search and replace
Swaps one piece of a string for another.
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Change the case
Converts a whole string to upper or lower case at once.
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Compare strings
Shows what ==, > and < do to text — not the same as with numbers.
pot
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Check how it starts or ends
Tests whether a string begins or ends with something.
pot
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Look at one character
Decides whether a single character is a digit, a letter, or a space.
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Turn text into a number
Converts what arrives over serial into an integer you can do maths with.
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Work out what a character is
Reports over serial whether what arrived is a digit, a letter, or punctuation.