My dear grandmother loves plants but she often forgets to water them. I designed and created this lovely device that provides a colorful emoticon display to alert owners when to water the plants. The moisture meter displays a smiling face if the plant has enough water, and it frowns/cries when the soil is arid.

Step 1: Required Materials

Arduino Uno Microcontroller Board

8X8 LED Matrix Array

Soil Humidity Sensor

Electronic Expansion Board

Battery

Alarm Buzzer (optional)

Step 2: Soldering the Components

Solder the LED matrix array, soil humidity sensor, and the alarm buzzer to the expansion board. For the LED matrix array, I connected CLK to pin #4, CS to pin #3, and DIn to pin #2. For the soil humidity sensor, the AO is connected to A5 on the Arduino unit. The alarm buzzer is connected to pin #5. If you happen to solder the inputs/outputs to different pins, remember to reroute to the appropriate pins in the Arduino code. Replace “Stick the battery to the back of Arduino” with Attach the battery power supply to the back of the Arduino unit.

Step 3: Battery

Attach the battery power supply to the back of the Arduino unit.

Step 4: Connect the Arduino Controller to the Rest of the Device.

Attach the Arduino unit to the expansion board to complete the assembly.

Step 5: Arduino Source Code

The last step is to load the following programming code onto the Arduino controller. Remember to modify the pin assignments if your selections differ from the instructions provided.

//Put the following code into Arduino

long soilhumid;

long humid;

int dataIn = 2;

int load = 3;

int clock = 4;

byte max7219_reg_noop = 0x00;

byte max7219_reg_digit0 = 0x01;

byte max7219_reg_digit1 = 0x02;

byte max7219_reg_digit2 = 0x03;

byte max7219_reg_digit3 = 0x04;

byte max7219_reg_digit4 = 0x05;

byte max7219_reg_digit5 = 0x06;

byte max7219_reg_digit6 = 0x07;

byte max7219_reg_digit7 = 0x08;

byte max7219_reg_decodeMode = 0x09;

byte max7219_reg_intensity = 0x0a;

byte max7219_reg_scanLimit = 0x0b;

byte max7219_reg_shutdown = 0x0c;

byte max7219_reg_displayTest = 0x0f;

int e = 0;

void putByte(byte data) {

byte i = 8;

byte mask;

while(i > 0) {

mask = 0x01 << (i - 1); // get bitmask

digitalWrite( clock, LOW); // tick

if (data & mask){ // choose bit

digitalWrite(dataIn, HIGH);// send 1

}else{

digitalWrite(dataIn, LOW); // send 0

}

digitalWrite(clock, HIGH); // tock

--i; // move to lesser bit

}

void maxAll(byte reg, byte col) {

digitalWrite(load, LOW); // begin

putByte(reg); // specify register

putByte(col);//((data & 0x01) * 256) + data >> 1); // put data

digitalWrite(load, LOW);

digitalWrite(load,HIGH);

}

void maxSingle(byte reg, byte col) {

digitalWrite(load, LOW); // begin

putByte(reg); // specify register

putByte(col);//((data & 0x01) * 256) + data >> 1); // put data

digitalWrite(load, LOW); // and load da stuff

digitalWrite(load,HIGH);

}

void setup()

{

Serial.begin(9600);

pinMode(dataIn, OUTPUT);

pinMode(clock, OUTPUT);

pinMode(load, OUTPUT);

maxAll(max7219_reg_scanLimit, 0x07);

maxAll(max7219_reg_decodeMode, 0x00);

maxAll(max7219_reg_shutdown, 0x01);

maxAll(max7219_reg_displayTest, 0x00);

for (e=1; e<=8; e++) { maxAll(e,0);}

maxAll(max7219_reg_intensity, 0x0f & 0x0f);

pinMode(0, OUTPUT);

soilhumid = 0;

humid = 0;

}

void loop()

{

// detect soil humidity

soilhumid = analogRead(A0);

Serial.println(soilhumid);

// lack water

if (soilhumid < humid) {

// sad face

maxSingle(1,0);maxSingle(2,102);maxSingle(3,102);maxSingle(4,0);maxSingle(5,60);maxSingle(6,66);maxSingle(7,66);maxSingle(8,0);// buzzer on

digitalWrite(0,HIGH);

delay(3000);

// buzzer off

digitalWrite(0,LOW);

} else {

// happy face

maxSingle(1,0);maxSingle(2,102);maxSingle(3,102);maxSingle(4,0);maxSingle(5,126);maxSingle(6,66);maxSingle(7,36);maxSingle(8,24);// buzzer off