Plant Monitor: Status Light

Part of the Projects section of Coddy's Arduino journey. Lesson 18 of 24.

Nobody reads a percent from across the room. A coloured light can be seen at a glance: red when the plant needs water, green when it is fine, blue when it has too much.

The status light is an RGB LED: three LEDs, red, green and blue, in one package, on pins 9, 10 and 6. Its common leg goes to ground, so a channel lights when its pin is HIGH. One colour at a time means one pin HIGH and the other two LOW.

Three ranges, three colours: the same if / else if / else shape as the parking sensor, starting from the bottom this time:

if (moisture < 30) {
  // dry: red
} else if (moisture <= 70) {
  // fine: green
} else {
  // wet: blue
}

Turn all three channels off first. Otherwise a red left over from before mixes with the new green, and the light turns yellow.

Challenge

Easy

Add the status light:

pins 9 (red), 10 (green) and 6 (blue) are outputs
under 30%: red only
30% to 70%: green only
over 70%: blue only

Update it after every reading. Press Run, turn the knob, then Check.

Try it yourself

// The knob stands in for a soil moisture sensor
const int sensorPin = A0;

// The moisture in percent: 0 is bone dry, 100 is soaking wet.
int readMoisture() {
  int reading = analogRead(sensorPin);
  return map(reading, 0, 1023, 0, 100);
}

void setup() {
  Serial.begin(9600);
}

void loop() {
  int moisture = readMoisture();
  Serial.print("Moisture: ");
  Serial.print(moisture);
  Serial.println("%");
  delay(1000);
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

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Practice on your own: Arduino playground