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PicoRuby Workshop 2025 - Microphone & ADC

Previous sections:

1. Setup + LED: https://tinyurl.com/picoruby-2025

In this section, we'll learn about analog-to-digital conversion (ADC) and explore how to read analog sensors. We'll use a microphone to detect sound levels and also explore the RP2350's built-in temperature sensor.

But first, let's learn how to write longer programs and run them as scripts!

From IRB to Ruby Scripts

So far we've been using IRB (Interactive Ruby) for quick experimentation. For longer programs, it's better to write Ruby scripts on your laptop:

The Workflow:

1. Experiment in IRB - Test your hardware connections and basic functionality
2. Write a script - Use your favorite text editor on your laptop to write a .rb file
3. Upload to R2P2 - Drag and drop the script file into the "home" directory of the R2P2 drive
4. Execute - Run the script from R2P2 shell with $> ./[script name].rb

Example: Save this as led.rb:

class LED < GPIO
  def initialize(pin)
    super(pin, GPIO::OUT)
  end

  def on
    write 1
  end

  def off
    write 0
  end

  def toggle
    high? ? off : on
  end
end

led = LED.new(16)
10.times do
  led.toggle
  sleep 0.5
end

Drag and drop led.rb into R2P2's home directory. Run ls in the R2P2 shell:

$> ls

You should see the file listed in the shell prompt.

Then run the script:

$> ./led.rb

What is ADC?

ADC (Analog-to-Digital Converter) converts continuous analog signals (like sound levels, temperature, or light intensity) into digital values that a computer can understand.

Think of it like translating a smooth curve into a series of discrete steps that represent the original signal.

The RP2350/RP2040 has a 12-bit ADC, which means:

• Range: 0 to 4095 (2^12 - 1)
• 0 represents 0 volts
• 4095 represents maximum voltage (3.3V for RP2350/RP2040)

Microphone Circuit

We'll use an analog microphone module to detect sound levels.

Components needed:

• 1x Analog microphone module (https://akizukidenshi.com/catalog/g/g105757/)
• 1x LED (from previous section)
• 1x 1kΩ resistor
• Jumper wires

Wiring:

RP2[3V3]  --- Microphone[VCC]
RP2[GND]  --- Microphone[GND]
RP2[GP26] --- Microphone[OUT(AUD)]

RP2[GP16] --- Resistor(1kΩ) --- LED[Anode(long leg)]
RP2[GND]  --- LED[Cathode(short leg)]

See the diagrams in the previous section for breadboard setup.

Pin Reference:

• GP26 is ADC0
• 3V3 (pin 36) is the 3.3V power output

Basic Sound Detection

Connection on the breadboard can be seen in the previous section.

Let's start with IRB to test our circuit:

irb> require 'adc'
irb> mic = ADC.new 26
irb> mic.read_raw
=> 2048  # Should be around 2048 (middle value) in silence
irb> mic.read
=> 1.65  # Voltage reading (around 1.65V in silence)

Try to check the values while clapping or speaking near the microphone.

Sound-Activated LED

Now let's create our first sound-activated circuit. Save this as sound_led.rb:

require 'adc'

led = GPIO.new(16, GPIO::OUT)
mic = ADC.new(26)

puts "Sound-activated LED started!"
puts "Clap or make noise to turn on the LED"

while true
  sound_level = mic.read_raw - 2048  # -2048..2047
  if 1000 < sound_level.abs  # Adjust threshold as needed
    led.write 1
    puts "Sound detected: #{sound_level}"
  else
    led.write 0
  end
  sleep 0.1
end

In R2P2 shell, Ctrl+C to stop the program.

Built-in Temperature Sensor

The RP2350 has a built-in temperature sensor that we can access through ADC:

irb> temp_adc = ADC.new :temperature
irb> temp_adc.read
=> 0.721  # This is the raw voltage from temperature sensor

Save this as temperature.rb and try running it:

require 'adc'

def voltage_to_celsius(voltage)
  reference_temp = 27.0
  reference_voltage = 0.706
  temp_coefficient = -0.001721

  temp_difference = (voltage - reference_voltage) / temp_coefficient
  reference_temp + temp_difference
end

temp_adc = ADC.new(:temperature)

while true
  voltage = temp_adc.read
  temperature = voltage_to_celsius(voltage)
  puts "Temperature: #{temperature.round(1)}°C"
  sleep 2
end

Unfortunately, the built-in sensor of the Raspi Pico is not very accurate. Please use this material as a reference when using discrete sensors.

Advanced Sound Level Monitor

Let's create a more sophisticated sound monitoring program. Save as sound_monitor.rb:

require 'adc'

led = GPIO.new(16, GPIO::OUT)
mic = ADC.new(26)
temp_adc = ADC.new(:temperature)

def voltage_to_celsius(voltage)
  reference_temp = 27.0
  reference_voltage = 0.706
  temp_coefficient = -0.001721

  temp_difference = (voltage - reference_voltage) / temp_coefficient
  reference_temp + temp_difference
end

puts "=== Sound & Temperature Monitor ==="
puts "Press Ctrl+C to stop"

loop do
  # Read sensors
  sound = mic.read_raw - 2048
  temp_voltage = temp_adc.read
  temperature = voltage_to_celsius(temp_voltage)

  # Sound detection with multiple thresholds
  if 1500 < sound.abs
    led.write 1
    puts "LOUD! Sound: #{sound}, Temp: #{temperature.round(1)}°C"
  elsif 500 < sound
    led.write(led.high? ? 0 : 1)  # Blink for moderate sound
    puts "Sound: #{sound}, Temp: #{temperature.round(1)}°C"
  else
    led.write 0
    puts "Quiet: #{sound}, Temp: #{temperature.round(1)}°C"
  end

  sleep 0.5
end

Exercises

For those who want to explore further:

1. Calibration: Create a calibration routine that measures the baseline noise level for 5 seconds and automatically sets the threshold.

2. Sound Patterns: Create different LED patterns for different sound levels:

   • Quiet: LED off
   • Moderate: Slow blink
   • Loud: Fast blink
   • Very loud: Solid on

3. Data Logging: Modify the sound monitor to keep track of:

   • Maximum sound level detected
   • Average sound level over time
   • Number of sound events above threshold

4. Multi-Sensor Dashboard: Combine multiple ADC readings:

   # Read multiple sensors and display formatted output
   def init
     @mic = ADC.new(26)
     @temp = ADC.new(:temperature)
   end
   
   def display_sensor_dashboard
     puts "┌─────────────────────────┐"
     puts "│ Sensor Dashboard        │"
     puts "├─────────────────────────┤"
     puts "│ Sound Level: #{@mic.read_raw.to_s.rjust(4)}      │"
     puts "│ Temperature: #{voltage_to_celsius(@temp.read).to_i}°C     │"
     puts "└─────────────────────────┘"
   end

5. Sound Trigger Recording: Create a system that detects when sound exceeds a threshold and records the maximum value reached during that "event":

   # Pseudo-code structure:
   # - Monitor continuously
   # - When sound > threshold, start "recording"
   # - Track peak value during the event
   # - When sound drops below threshold for 1 second, end recording
   # - Display event summary (duration, peak value)