Capacitive Soil Moisture Sensor Raspberry Pi

 

1. Introduction

The Capacitive Soil Moisture Sensor measures the moisture content in soil using capacitive sensing, which is more durable than resistive sensors. Since it gives an analog output, we use the MCP3008 to interface it with the Raspberry Pi.

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2. Components

• Raspberry Pi 4 Model B
• MCP3008
• Capacitive Soil Moisture Sensor
• Breadboard
• Jumper wires

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3. Circuit and Connections

Raspberry Pi Pinout Diagram

Soil Moisture Sensor Pinout Diagram

MCP3008 Wiring Diagram

MCP3008 ADC Pinout Diagram

Sensor to MCP3008

Sensor Pin	Connection
VCC	3.3V
GND	GND
AOUT	MCP3008 CH0

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MCP3008 to Raspberry Pi (SPI Connection)

MCP3008 Pin	Function	Raspberry Pi Pin
16	VDD	3.3V
15	VREF	3.3V
14	AGND	GND
13	CLK	GPIO11 (SCLK)
12	DOUT	GPIO9 (MISO)
11	DIN	GPIO10 (MOSI)
10	CS/SHDN	GPIO8 (CE0)
9	DGND	GND

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4. Detailed Step By Step Circuit Working

1. Sensor measures soil moisture based on capacitance
2. Output voltage changes with moisture level
3. MCP3008 converts analog voltage to digital value
4. Raspberry Pi reads digital data via SPI
5. Higher value → Dry soil, Lower value → Wet soil

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5. Libraries to be Included

pip3 install spidev

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6. Code (Python)

import spidev
import time

spi = spidev.SpiDev()
spi.open(0, 0)
spi.max_speed_hz = 1350000

def read_channel(channel):
    adc = spi.xfer2([1, (8 + channel) << 4, 0])
    data = ((adc[1] & 3) << 8) + adc[2]
    return data

try:
    while True:
        moisture = read_channel(0)

        print("Soil Moisture Value:", moisture)

        if moisture > 700:
            print("Dry Soil")
        elif moisture > 400:
            print("Moderate Moisture")
        else:
            print("Wet Soil")

        print("---------------------")
        time.sleep(1)

except KeyboardInterrupt:
    spi.close()

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7. Detailed Step By Step Code Working

• Reads analog value via MCP3008
• Converts to digital (0–1023)
• Compares values to determine moisture level
• Prints status (Dry / Wet)
• Loops continuously

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8. Tips

• Do not power with 5V (use 3.3V)
• Avoid immersing full sensor in water
• Calibrate values for your soil type
• Use corrosion-resistant sensor (capacitive type)
• Keep wiring short

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9. Uses

• Smart irrigation systems
• Agriculture automation
• Plant monitoring
• Greenhouse control
• IoT farming projects

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10. Conclusion

The capacitive soil moisture sensor is reliable and long-lasting. With MCP3008, Raspberry Pi can easily monitor soil conditions for smart agriculture systems.