Lesson 14 of 16

Plant monitor

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#include <Wire.h> #include <Adafruit_SSD1306.h> const int SENSOR = A0; const int DRY = 520; // the reading in dry air const int WET = 260; // the reading in a glass of water Adafruit_SSD1306 screen(128, 64, &Wire); void setup() { Serial.begin(9600); screen.begin(SSD1306_SWITCHCAPVCC, 0x3C); // 0x3C is the screen's I²C address screen.setTextColor(SSD1306_WHITE); } void loop() { int raw = analogRead(SENSOR); int moisture = map(raw, DRY, WET, 0, 100); // turn the reading into 0-100 % moisture = constrain(moisture, 0, 100); Serial.println(moisture); screen.clearDisplay(); screen.setTextSize(3); screen.setCursor(0, 0); screen.print(moisture); screen.print("%"); screen.drawRect(0, 28, 128, 8, SSD1306_WHITE); screen.fillRect(0, 28, moisture * 128 / 100, 8, SSD1306_WHITE); // smaller text for the message screen.setTextSize(2); screen.setCursor(0, 46); if (moisture < 30) { screen.print("Water me!"); } else if (moisture > 85) { screen.print("Too wet!"); } else { screen.print("Happy :)"); } screen.display(); delay(500); }

Stopped · Your code isn't running yet. Until you press Run, the board runs the program already on it.

Nothing printed yet. Press Run.

A soil probe says how wet the soil is; an OLED screen shows it as a percentage and a bar, and tells you when to water.

Calibrate with a dry and a wet reading
Two wires carry everything to the screen
Water it and watch the bar fill

Pin	Connects to	What it does
`5V`	The soil probe's VCC	Powers the probe.
`A0`	The soil probe's AOUT	Lower voltage means wetter soil.
`3V3`	The OLED's VCC	Powers the screen.
`SCL-SDA`	The OLED's SCL and SDA	I²C: clock and data on two wires.

Wire it in

Sensors and actuators this board drives, with the real connections.

PotentiometerSupply 5 V
Ends to GND and 5V, the middle leg (wiper) to A0. analogRead(A0) then goes from 0 to 1023 as you turn it.
Part pin Board pin
1 GNDWire colour black
2 A0Wire colour green
3 5VWire colour red
Light sensor (LDR)Supply 5 V
From 5V to A0, with a 10 kΩ resistor from A0 to GND. More light, lower resistance, higher reading.
Part pin Board pin
1 5VWire colour red
2 A0Wire colour green
TMP36 temperature sensorSupply 5 V
Flat face toward you: left leg 5V, middle leg to A0, right leg GND. Degrees C = (volts − 0.5) × 100.
Part pin Board pin
VS 5VWire colour red
VOUT A0Wire colour green
GND GNDWire colour black
Capacitive soil moisture sensorSupply 5 V
AOUT to A0, VCC to 5V, GND to GND. The reading falls as the soil gets wetter.
Part pin Board pin
AOUT A0Wire colour yellow
VCC 5VWire colour red
GND GNDWire colour black
FSR 402 force sensorSupply 5 V
One leg to 5V, the other to A0, with a 10 kΩ pull-down from A0 to GND. Press harder, read higher.
Part pin Board pin
1 5VWire colour red
2 A0Wire colour green

Part pin	Board pin
1	GNDWire colour black
2	A0Wire colour green
3	5VWire colour red

Part pin	Board pin
1	5VWire colour red
2	A0Wire colour green

Part pin	Board pin
VS	5VWire colour red
VOUT	A0Wire colour green
GND	GNDWire colour black

Part pin	Board pin
AOUT	A0Wire colour yellow
VCC	5VWire colour red
GND	GNDWire colour black

Part pin	Board pin
1	5VWire colour red
2	A0Wire colour green

All 16 parts on the Arduino Uno R3 page

Plant monitor

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in

Plant monitor

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in