Read a Sensor

Analog input gives you a range instead of a yes/no answer. On ESP32-class boards the raw ADC reading is usually a 12-bit count from 0 to 4095.

On the Froth Machine, the easiest analog sensors are already mounted: the left and right knobs.

Read A Raw ADC Pin

On a general board:

adc.read: A0

Turn the potentiometer or change the sensor voltage and read again. The number should move.

Convert a raw count to a percentage:

to adc.percent.of with raw [
  raw * 100 / 4095
]

adc.percent.of: (adc.read: A0)

The board library already provides the usual helper:

adc.percent: A0

Use the helper unless you are teaching or debugging the conversion.

Read The Machine Knobs

On the Froth Machine:

knob.left:
knob.right:
knob.left.raw:
knob.right.raw:

The knob.left and knob.right helpers return a percentage-style value on the 0..100 scale. The .raw forms return the ADC sample.

Map A Sensor To A Pixel

Initialize the display:

matrix.init:
matrix.brightness!: 1

Scale the left knob to an x coordinate:

to knob.x [
  (knob.left:) * (grid.width - 1) / 100
]

Draw one frame:

sensor.frame is fn [
  grid.clear:;
  grid.set: knob.x:, 3, true;
  grid.show:
]

Run it:

repeat 300 [
  sensor.frame:;
  ms: 25
]

Turn the knob. The lit pixel should move across the display.

Add A Threshold

Thresholds are clearer when named:

alert.threshold is 70

Light the built-in LED when the knob crosses the threshold:

alert.frame is fn [
  if (knob.left:) > alert.threshold [
    led.on:
  ] else [
    led.off:
  ]
]

Run both the display and LED behavior in one frame:

sensor.alertFrame is fn [
  sensor.frame:;
  alert.frame:
]

That is the analog input pattern: read the raw world, scale it to the range your program uses, and keep the conversion in one named place.