Analog signals

What is an Analog Signal?

Nature works in the analogic way, think about temperature, light, sound, etc. For example, in the city that I live (Guadalajara, México) temperatures in summer are in the range of 65 to 95 °F. So if I measure the temperature during the day using a mercury thermometer I will notice that temperature its in one point 70 then 1 second later may be 70.00…1 where “…” means alot of zeros cause it only raises almost nothing, and then 1 hour later it could be 73 1/3. We know that 1/3 equals to 0.33333 with infinite 3’s.

So with these examples now I can tell you that an analog signal has a determined value for each time instant. And it could be any number even an irrational number (like pi). See the next graph were it represented an analog voltage signal.

analog_signal

You can see that at any time from the beginning to the end it has values that goes from ~1V (looks like it goes down less than 1/3 of 3.3V)  to 3.3V. So in order to these groups of values can be processed into a microcontroller we need to do 2 operations: Round to a certain groups of values and represent them with numbers.

So we need to convert our analog signal into a digital discrete signal. This task is made by an Analog to Digital Converter (ADC). I’m not going to cover in depth how a ADC works. You only need to know (by now) two things about ADCs: Resolution and range.

digital-discrete-signal_dots

The voltage range supported by the ADCs its between 0 and 3.3 volts. So when connectting a circuit make sure (better twice) that your not supplying more than 3.3 volts, this will permanently damage your board.

The resolution of the ADC is 16 bits, this means that the minimum change that can it detect is 1/65535 this is approximately 0.000015259 Volts or 15.259 micro-volts.  In order words it can detect very small variations in voltage.

Playing with analog signals

Check the next sections to play with analog signals:

  • Reading a potentiometer
  • Reading a light dependent resistor (LDR)
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