A microcontroller (sometimes abbreviated MCU) is a small computer on a single integrated circuit containing a processor core, memory, and usually from several to dozens of general purpose input/output pins (GPIO). GPIO pins are software configurable to either an input or an output state. When GPIO pins are configured to an input state, they are often used to read sensors or external signals. Configured to the output state, GPIO pins can drive external devices such as LEDs or motors, often indirectly, through external power electronics.
Read more on Wikipedia
Interesting MCUs for a hobbyist include at least the Atmega328 that's used in Arduinos, the ESP8266 that includes in integrated Wifi circuit.
Arduino is family of microcontroller boards, many of which contain the Atmega328 MCU. In addition to the MCU, the Arduino boards typically feature a voltage regulator (see below) and an USB port for easy communications with a host computer. The Arduino boards typically also act as "breakout boards" for easily connecting the MCU GPIO pins to your periphrals of choice. My first Arduino board was the Arduino Uno, pictured below.
![https://upload.wikimedia.org/wikipedia/commons/3/38/Arduino_Uno_-_R3.jpg]
Arduino IDE is a programming environment that you can use to upload a "sketch" onto an Arduino board. The sketches are programmed in C++. In addition to actual Arduinos, you can use the Arduino IDE and related host of additional libraries for some other microcontrollers, such as the ESP8266 via "plugins".
A breadboard is a construction base for prototyping of electronics. It allows you to plug electronic components together using jump wires, without having to solder anything together.
![https://en.wikipedia.org/wiki/Breadboard#/media/File:Breadboard.JPG]
I assume you understand the concepts of voltage, current and power already, so I'll cover those from a perspective that's practical from the IoT hobbyiests point of view.
Your devices will typically need some DC power to work. Voltage is key; if you don't supply enough voltage, your device won't work. If you supply too much, it'll probably heat up and go out in flames. So pay attention to the minimum/maximum voltage specs of your devices. Typically, digital components like microcontrolller operate at 3.3 or 5 volt and have some tolerance with regard to voltage. For example, the ESP8266 microcontroller operates at 3.3 volts but practically runs just fine with 2 AA batteries that provide 3 volts in total.
A voltager regulator is a component that takes a range of input voltages (say, 6 to 12 volts) and outputs a steady output voltage (say, 5 volts). The Arduino boards feature a voltage regulator, so they are not so picky about input voltage.
Your components will draw some amount of current from their power source. For instance an Arduino might draw 30 mA (milliamperes) at 5 volts. From this you can calculate the power consumption of about 150 milliwatts.
TODO: mAhs, maximum output currents of things
In digital logic circuits a pin (let's say a GPIO pin on your arduino) can be in 3 different states:
- Up: the pin has a voltage above the "high" threshold of you MCU. In a typical Arduino setup, a pin that's said to be "up", is at 5 volts
- Down: the pin is pulled down, i.e. connected to ground
- Floating: the pin is connected to neither "high" or ground. When your input GPIO pin is floating, there's no guarantee on the value you can read from it.
So, if your reading a digital value from a GPIO pin, make sure it's not floating. You can do this by applying a pull-up or pull-down resistor.
Some typical devices compared.
| Platform | Specs | Voltage | mA | Battery life ~ |
|---|---|---|---|---|
| Raspbberry Pi | 1Ghz, any flash | 3.3v | 400mA | 3AA, 3 hours |
| Arduino | 16Mhz, 32kb flash | 5v | 33mA | 4AA, 3 days |
| Bare Arduino | 16Mhz, 32kb flash | 3v | 10mA | 2AA, 10 days |
| Bare Arduino deep sleep | 3v | 10uA | 2AA, 25 years | |
| ESP8266 / ESP01 | 80Mhz, 512kb flash | 3v | 70mA | 2AA, 30 hours |
| ESP8266 deep sleep | 3v | 30uA | 2AA, 12 years |
I measured the currents (mA ratings) myself. AA battery mAh ratings are from from http://www.powerstream.com/AA-tests.htm. The battery life figures are rough estimates. The ones exceeding 1 year will probably be dominated by self-discharging of the AA cells and in real worlds, you won't experience anything like a 25 year battery life.
So if you're looking at making a battery-powered device that's always on, you'll probably need a platform that can go to a deep-sleep mode. That will work for, for instance, sensors that transmit something once in 5 minutes or so.
If, on the other hand, you can plug into AC power, you can use a Raspberry Pi and enjoy the power of a full-fledged Linux machine, yet with GPIO capabilities for interacting with sensors and other devices.
Here are some things that you'll have to take into account when designing your device.