Microcontrollers

A computer on a chip

Some computers are obvious, like laptops and phones. Many others are hidden inside everyday things, by the hundreds in appliances, cars and personal electronics.^[1] These hidden computers are microcontrollers.

A microcontroller combines the same basic parts as a microprocessor, a processor (CPU) and memory (ROM and RAM), on a single chip.^[1] Arduino’s documentation calls it “a tiny computer, designed to execute only a specific number of things”.^[3]

Microprocessor or microcontroller?

The two are close cousins:

• A microprocessor is a computer’s processor on a single chip. Intel’s 4004 of 1971, with 2,300 transistors, is an early example,^[2] which Intel describes as the first general-purpose microprocessor.^[5] It was built for the Busicom 141-PF printing calculator.^[5]
• Single-chip solutions offering limited functionality for a specific application are called microcontrollers.^[2]

Inputs and outputs

A microcontroller earns its keep by reacting to the world. In Arduino’s terms, sensors are inputs: they measure things like temperature or detect a button press. Actuators are outputs: they change something physical, like lighting an LED or turning a motor.^[3]

Signals come in two kinds:^[3]

• Digital signals have just two states, 0 or 1 (off or on).
• Analog signals can take any value within a range. On Arduino boards, an input between 0 and 5 volts is read as a number from 0 to 1023.

Arduino boards can also talk to a computer over a serial connection, which Arduino calls the easiest way to find out what is going on inside your board.^[3]

How a microcontroller is programmed

You write a program on a computer. It is then compiled, meaning converted into a binary file of 1s and 0s, and uploaded to the board.^[3] The microcontroller stores the program and runs it every time it powers up.

Arduino programs, called sketches, have two main parts: setup() runs once when the board is powered on, and loop() contains the code that runs over and over again.^[3] Pre-written libraries extend the basic commands, so you don’t have to write everything yourself.^[3]

A short history

In 1974 Texas Instruments announced the TMS 1000, a general-purpose 4-bit microcontroller. It held the same basic ROM, RAM and CPU elements as a microprocessor on one chip, and sold for about $2 in volume.^[1] It found its way into burglar alarms, garage door openers, games and toys such as Speak & Spell, bringing digital electronics to consumers.^[1]

Today, according to the Computer History Museum, microcontrollers are hidden by the hundreds in appliances, automobiles and personal electronics, and may be the most widespread semiconductor device of all.^[1]

Going further

• Arduino is the easiest way to start programming a microcontroller yourself.
• Transistors explains the tiny switches a microcontroller is built from.