Embedded Systems: microcontrollers and sensors

01

Doing many jobs at once: millis() and state machines

In simple words

Imagine you are cooking soup and also watching a pot of rice. If you stand still and stare at the soup for ten minutes, the rice burns. A good cook glances at the clock, does a bit of each job, and keeps moving. A good program does the same: it checks the clock instead of freezing.

Key facts

An embedded system is a small computer built into a device to do one set of jobs, usually with sensors in and actuators out. A microcontroller board is the usual starting point.
delay(1000) stops your code for a second. Nothing else (reading a button, updating a display) can run during it.
millis() returns the milliseconds passed since the program began. Its data type is unsigned long, and it overflows (goes back to zero) after about 50 days.
Non-blocking timing pattern: save the time of the last action, and each pass through loop() check whether enough time has gone by. Compare with subtraction: now - last >= interval. With unsigned numbers, subtraction keeps working even when the counter wraps back to zero.
A state machine is a program that is always in exactly one named state (for example IDLE, MEASURING, ALARM) and has rules for moving to the next state. It keeps long programs organised and easy to test.

Example (blink and read at the same time)

const unsigned long BLINK_MS = 500;
unsigned long lastBlink = 0;
bool ledOn = false;

void setup() {
 pinMode(LED_BUILTIN, OUTPUT);
 Serial.begin(9600);
}

void loop() {
 unsigned long now = millis();
 if (now - lastBlink >= BLINK_MS) {
  lastBlink = now;
  ledOn = !ledOn;
  digitalWrite(LED_BUILTIN, ledOn);
 }
 // other jobs can run here every pass, for example reading a button
}

Example (states)

State	What it does	Moves to
IDLE	Waits	MEASURING every 2 seconds
MEASURING	Reads the sensor	ALARM if the value is too high, otherwise IDLE
ALARM	Flashes an LED	IDLE when a button is pressed

Step by step

Open the Arduino IDE and start a new sketch.
Type the non-blocking blink from the lesson and upload it.
Add a second job in loop() that prints millis() once per second using its own last variable and the same subtraction pattern.
Watch the LED blink and the Serial Monitor print at the same time.
Replace one delay() in an old sketch of yours with the millis() pattern.
Draw the state table for a project idea: states, what each does, and what moves it to the next state.
Check: two jobs run at different rhythms and neither one freezes the other.

Watch on YouTube

Walk away from delay: using millis()talofer99 · YouTube · youtube.com

Videos by other creators on YouTube, for reference. They are not made by or affiliated with The Future Market.

LESSON 01Doing many jobs at once: millis() and state machines

LESSON 01 / ANIMATED LESSON / AI VOICE00:00 / 01:15

Voice

Read the video script

[Host] "Delay is a trap. While your code sleeps, it cannot see a button or a sensor."
[Screen: timeline with two blinking LEDs at different speeds] "Instead, ask the clock: how long since I last did this?"
[Text on screen: now - last >= interval] "Subtract, compare, and update the time you last acted."
[Screen: three boxes IDLE, MEASURING, ALARM with arrows] "Then give your program named states. It is always in exactly one."
[Host] "Small tasks, a clock and states: that is how real devices multitask."

Try it now

Write a sketch that blinks one LED every 300 ms and prints a counter every 2 seconds, with no delay() anywhere. Then draw its state table on paper. If you have no board, use a free simulator and print messages instead of lighting an LED.

ClaudeStuck? Copy a ready-made prompt for Claude

Copy this, open Claude, paste it, and Claude will walk you through the lesson step by step.

For a grown-up: Claude is for adults (18+). Copy this, paste it into Claude, and use the answer to explain the lesson to your child.

I'm learning "Embedded Systems: microcontrollers and sensors" on The Future Market. Lesson 1: "Doing many jobs at once: millis() and state machines".

What the lesson teaches:
- An embedded system is a small computer built into a device to do one set of jobs, usually with sensors in and actuators out. A microcontroller board is the usual starting point.
- delay(1000) stops your code for a second. Nothing else (reading a button, updating a display) can run during it.
- millis() returns the milliseconds passed since the program began. Its data type is unsigned long, and it overflows (goes back to zero) after about 50 days.
- Non-blocking timing pattern: save the time of the last action, and each pass through loop() check whether enough time has gone by. Compare with subtraction: now - last >= interval. With unsigned numbers, subtraction keeps working even when the counter wraps back to zero.
- A state machine is a program that is always in exactly one named state (for example IDLE, MEASURING, ALARM) and has rules for moving to the next state. It keeps long programs organised and easy to test.

The exercise I'm working on:
Write a sketch that blinks one LED every 300 ms and prints a counter every 2 seconds, with no delay() anywhere. Then draw its state table on paper. If you have no board, use a free simulator and print messages instead of lighting an LED.

I'm stuck. Please:
1. Explain the main idea in plain, simple words with one everyday example.
2. Walk me through the exercise one small step at a time. Ask me what I've done so far before giving the next step.
3. Don't just give me the final answer. Help me do it myself, and check my work when I share it.

I'm a parent helping my child (about 8 years old) with a lesson called "Doing many jobs at once: millis() and state machines" from the course "Embedded Systems: microcontrollers and sensors".

Here's what the lesson says:
Imagine you are cooking soup and also watching a pot of rice. If you stand still and stare at the soup for ten minutes, the rice burns. A good cook glances at the clock, does a bit of each job, and keeps moving. A good program does the same: it checks the clock instead of freezing.

The activity:
Write a sketch that blinks one LED every 300 ms and prints a counter every 2 seconds, with no delay() anywhere. Then draw its state table on paper. If you have no board, use a free simulator and print messages instead of lighting an LED.

Please explain this so an 8-year-old understands: short sentences, a fun everyday example, and no hard words.
Then give me 3 simple questions I can ask my child to check they understood, and a way to do the activity together, one tiny step at a time.

Open Claude

Sources

Arduino reference, millis() (unsigned long, overflows after about 50 days): github.com/arduino/reference-en/blob/master/Language/Functions/Time/mi
Arduino reference, Language Reference: docs.arduino.cc/language-reference/

My notes

I learned this

02