Analog to Digital Conversion

Analog to Digital Conversion

Analog vs. Digital

• Analog: infinite variations / states
• Digital: discrete (or finite) states
• How do we represent infinite variations in a system that has limited / finite values?

Analog to Digital Conversion

• Photon 2 is a digital system so we need to convert the infinite analog input to a discrete values
• At regular intervals, the Photon 2 samples (“reads”) voltage on analog input pin it sees
  • The sampling frequency is how many times per second
• The resolution is how many bits are used to store the voltage
  • Higher resolution means greater detail, but also more bits (more memory)

Understanding Resolution

• Red line is actual analog input voltage (in volts)
• Blue line is the digital sample value (just a number with no units)

Photon 2 ADC Resolution is 12-bits

• When we read the analog input voltage, ADC converts the voltage to a number
• There 2^12=4096 possible values (think “buckets”)
• In Binary
  • 0 = 000000000000
  • 4095 = 111111111111

ADC Pins

• A0
• A1
• A2
• A5
• A3 (SDA or D0)*
• A4 (SCL or D1)*

You can use either of these pins labels

Photon 2 ADC

• The range of analog voltage is 0v to 3.3v
• The range of digital values is 0 to 4095
• Q: How many digital values per 1v?
• Q: How many volts per each digital value?
• Q: If there is 3.3v on an analog input, what is the value of analogRead()?
• Q: If there is 1.67v on an analog input, what is the value of analogRead()?

Exercise

• Connect potentiometer to A0
• Connect LED to pin A2 (do we need a pin with PWM?)
• Control LED brightness with potentiometer

Credit

• Hyacinth
• Hyacinth