← Electronics & Arduino

World 1 · Foundations

1What is electricity?2Voltage, Current, Resistance 3Your first circuit 4Ohm’s Law in practice 5Reading resistor colors 6Inside the atom 7Electric charge 8Conductors vs insulators 9Current, up close 10Voltage, up close 11Resistance, up close 12Rearranging Ohm’s Law 13The closed loop 14Batteries & cells 15Cells in series 16The LED 17Current-limiting resistors 18The resistor color code 19Power & watts 20Energy & your bill 21Short circuits 22Open circuits 23Switches 24Ground & reference 25Schematic symbols 26Using a multimeter 27Ammeter vs voltmeter 28AC vs DC 29Frequency 30Static electricity 31Electromagnetism 32A taste of parallel

World 2 · Circuits · PRO

1Series vs Parallel 2The breadboard 3Switches & buttons 4The voltage divider 5Series circuits in depth 6Parallel circuits in depth 7Choosing series or parallel 8Building on a breadboard 9Momentary vs latching 10Pull-up resistors 11Pull-down resistors 12Voltage divider math 13The potentiometer 14The LDR (light sensor)15The thermistor (temp sensor)16Capacitors 17What capacitors are for 18The diode 19The LED as a diode 20Rectification intro 21Transistor as a switch 22Transistor as amplifier 23The relay 24Logic gates 25Combining gates 26RC timing 27Current limiting in depth 28Kirchhoff’s voltage law 29Kirchhoff’s current law 30Measuring a divider 31Decoupling capacitors 32Troubleshooting a dead circuit

World 3 · Arduino 101 · PRO

1Meet Arduino Uno 2Blink — your first sketch 3Digital output: traffic light 4Digital input: a button 5The Serial Monitor 6The Arduino IDE & sketch 7Blink speed & timing 8LED_BUILTIN 9Two LEDs alternating 10Traffic light with helper 11LED chase (array + for)12Knight Rider scanner 13Variables & math 14if / else decisions 15for loops 16while loops 17Writing functions 18Blink without delay (millis)19Button controls an LED 20Why INPUT_PULLUP?21Toggle on each press 22Debouncing a button 23Button press counter 24Two buttons, up & down 25Serial: print vs println 26Serial number bases 27Random blinks 28Digital vs analog pins 29do / while loops 30Capstone: non-blocking traffic light

World 4 · Arduino Projects · PRO

1Fading an LED (PWM)2Reading a potentiometer 3Servo control 4Buzzer & tone 5Automatic night-light 6How PWM really works 7Breathing LED 8RGB LED colour mixing 9RGB rainbow fade 10Mood lamp 11Inside a servo 12Servo sweep 13Smooth servo steering 14Play a melody 15Police siren 16Reaction-time game 17Serial bar meter 18How analog sensors work 19Light-level logger 20Light theremin 21Reading temperature 22Thermostat 23DC motor speed control 24Smart fan controller 25Ultrasonic distance 26Parking sensor 27Radar sweep 28Pedestrian crossing 29Two-button dimmer 30Combination lock

World 5 · Power & Regulation · PRO

1Where power comes from 2Reading a power rating 3Battery capacity & runtime 4Mains & the transformer 5The bridge rectifier 6Smoothing & ripple 7The linear regulator 8Why regulators run hot 9The buck converter 10The boost converter 11Choosing a regulator 12Powering an Arduino properly

World 6 · Op-Amps & Analog Blocks · PRO

1What an op-amp does 2The two golden rules 3The comparator 4Hysteresis and the Schmitt trigger 5The buffer 6The non-inverting amplifier 7The inverting amplifier 8The summing amplifier 9The difference amplifier 10Single supply and virtual ground 11Where the golden rules stop 12Amplifying a sensor signal

World 7 · Practical Design · PRO

1Why 4.7 kΩ and never 5 kΩ 2How much energy a capacitor holds 3The Zener diode 4The MOSFET as a switch 5RC filters 6Reactance 7The 555 timer 8Voltage drop in the wires 9How wide does a PCB track need to be?

World 8 · Screens & I²C · PRO

1The 16×2 character display 2Six wires to a screen 3The cursor is the whole API 4Why your number leaves a 0 behind 5Putting a measurement on the screen 6The display that shows nothing 7I²C: two wires, many devices 8The same display, on two wires 9A clock that keeps time without you

World 9 · Sensors · PRO

1What a sensor gives you 2The DHT22: temperature and humidity 3Feels like: the heat index 4The thumb joystick 5The rotary encoder 6The encoder on an interrupt 7Smoothing noisy readings 8Capstone: a climate display

World 10 · Pixels & Digits · PRO

1The seven-segment digit 2A digit is a byte 3Counting, and a dice you roll 4NeoPixels: one wire, many LEDs 5Colour by angle: HSV 6The power budget 7Capstone: a level meter

World 11 · Internet of Things · PRO

1What "connected" actually means 2Joining a network 3Asking for something: HTTP GET 4Reading an answer by hand 5A switch you are not standing next to 6Sending data: HTTP POST 7Asking politely 8Capstone: a connected weather station

World 12 · Motion · PRO

1Three ways to make things move 2Why a motor can’t hang off a pin 3The H-bridge 4Speed and direction together 5The stepper motor 6Homing with a limit switch 7Pan and tilt with a joystick 8Capstone: a dial-controlled joint

World 13 · Digital Logic · PRO

1Why digital means two states 2Binary is place value 3Hexadecimal: one digit per nibble 4De Morgan’s laws 5Parity: XOR counts the 1s 6The half adder 7The full adder 8Comparing two numbers in logic 9Decoding a number for a display 10Capstone: a 2-bit adding machine

World 14 · Talk to your Arduino · PRO

1The line that goes the other way 2From characters to a line 3Reading a number 4A tiny command language 5A command shell

World 15 · Soldering & Real Builds · PRO

1Tools, heat and safety 2A good joint, and a bad one 3Soldering a through-hole part 4Desoldering and fixing mistakes 5From breadboard to a board that lasts

World 16 · Raspberry Pi & GPIO · PRO

1What is a Raspberry Pi?2The GPIO header 3Your first blink 4Why the LED needs a resistor 5Sequences and timing 6PWM: brightness, not just on 7Reading a button 8Making sound 9Keeping state 10When it breaks

World 17 · Build Projects · PRO

1Turn On Your First LED 2Your First Blink 3Traffic Light 4Distance Alarm 5Night Light 6Morse Beacon 7Candle Flicker 8Heartbeat LED 9RGB Mood Lamp 10Fan Speed Controller 11Servo Gauge 12Temperature Warning 13Plant Water Meter 14Sunrise Alarm 15Parking Assistant 16Button-Controlled Lamp 17Dimmer Knob 18Doorbell 19Breathing LED 20Light Theremin 21Alternating Blinkers 22Cooling Fan 23Barrier Gate 24Distance Theremin 25LCD Thermometer 26Electronic Dice 27NeoPixel Level Meter 28Stepper Seconds Hand 29Joystick Camera Pan 30Volume Knob 31Desk Clock 32Greenhouse Logger 33Remote Lamp

World 18 · Circuits & Signals · PRO

1RC charging and the time constant 2The RC low-pass filter 3Series RLC: resonance and ringing 4Op-amp amplifiers and clipping

World 7 · Practical Design · 8 min · PRO

The 555 timer

Two resistors, one capacitor, any frequency you like

PRO · Electronics & Arduino

World 7: Practical Design is part of PRO

The first world of Electronics & Arduino is free. PRO opens the other 232 lessons in 17 worlds — simulations, quizzes and all.

Why 4.7 kΩ and never 5 kΩ
How much energy a capacitor holds
The Zener diode
The MOSFET as a switch
RC filters

PRO includes

All 26 labs — every world, every lesson
Practice exams and certificates

$8.33/mo, billed yearly ($99.99) · or $39.99 monthly

Unlock Electronics & Arduino Try the free world

← Reactance Voltage drop in the wires →

Report a mistake

What is wrong?Wrong or outdated factTypo or unclear textSimulation or quiz not workingOther

Tell us what you saw0 / 2000 · at least 10 characters

E-mail (optional, if you’d like a reply)

Website

Sent along with your report

Page
About The 555 timer — Electronics & Arduino · electronics/pd7-555-timer

Plus your browser type. Reports go to our support system; see the privacy notice.