How is a pin designed to be analog or digital on a Arduino/Raspberry Pi board? I don't mean what is the difference between analog or digital, or what functions do I need to use to write an analog/digital signal. I mean on one of these boards, certain pins are called "analog" pins and unlike digital pins, the analog pins can detect more values than just "ON" and "OFF." How is this feature implemented on the circuit board (i.e. the hardware)? Does the chip on the board have something to do with it? Where can I learn more about this?
Electronic – arduino – How is a pin designed to be analog or digital on a Arduino/Raspberry Pi board
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Related Solutions
Like you already suspect a DMM won't give you necessarily the answer. If the only levels you read are only 3.3V (capital "V", since it's derived from a person's name) and 0V it's a safe bet that it's digital. A PWM signal is also digital, but will show a voltage between 3.3V and 0V on a DMM, since it includes a low-pass filter. The DMM won't tell an analog and PWM signal apart. You'll need an oscilloscope to actually see what the signal looks like.
If you can trace the signal back to the output of a microcontroller, without filtering, it's most likely a digital signal. While most microcontroller families are available with on-chip ADC, very few also have DACs on board.
If you're already familiar with digital multiplexer chips, good news! They can be used for analog signals as well.
http://playground.arduino.cc/Learning/4051
The basic premise is exactly like with digital signal multiplexing. You use the 4051 chip as a "lane changer" and read the signal of whatever lane you tell the chip to switch to. the 4051 uses 3 digital pins and 1 additional analog (or digital) pin on the arduino to create up to 8 lanes of input. Some multiplexers are chainable, so you can fairly easily add 8 more signals without needing to keep taking them away from the arduino itself.
It is exactly like the technique you already know for digital signals, just hook up the channel you read from to an analog pin instead of a digital one, then cycle through the binary states and read the analog values.
I made an animated gif for you.
Best Answer
Those analog pins has an ADC embedded in them. Generally, a single pin is connected to a lot of Peripherals, the GPIO (General Purpose Input Output) peripheral is responsible to give a digital output or digital read. Most of the pin has GPIO MUXED in them.Other example of peripherals are PWM, CAP etc. For Analog read, we have ADC peripheral. The number of ADC peripheral are limited in number, but single ADC has multiple channels, which means the ADC can only convert one channel at a time.
You can learn about them from their respective Datasheets and Technical References.