Reading Analog Sensors with Raspberry Pi and Zabbix: A Step‑by‑Step Guide

Reading Analog Sensors with Raspberry Pi and Zabbix

Although the Raspberry Pi lacks native analog inputs, the MCP3008 10‑bit, 8‑channel ADC makes it trivial to add analog capabilities. It plugs directly into the Pi’s GPIO header via the SPI bus and requires no extra components.

This tutorial walks you through wiring an MCP3008 to the Pi, reading a light‑dependent resistor (LDR) with Python, and feeding the data into Zabbix for monitoring.

The hardware:

• Raspberry Pi
• MCP3008 8‑channel ADC
• Light dependent resistor (LDR)
• 10 kΩ resistor
• Breadboard
• Some wiring

Understanding the SPI Bus

The MCP3008 transmits a 10‑bit digital value over the SPI interface, a full‑duplex synchronous serial protocol that operates in master/slave mode. Multiple slaves can share the bus, each selected by its own CS line.

On the Raspberry Pi, SPI is exposed via the 4‑pin header (GPIO8, 9, 10, 11). To enable the hardware SPI driver, edit the blacklist file:

sudo nano /etc/modprobe.d/raspi-blacklist.conf

Locate the line containing spi-bcm2708 and prefix it with a # to comment it out. Save and reboot:

sudo reboot

After reboot, verify that the driver is loaded:

lsmod | grep spi_bcm2708

You should see spi_bcm2708 listed.

Installing the Python SPI Library

To access the SPI bus from Python we’ll use py-spidev. First install the development headers for Python:

sudo apt-get install python-dev

Next download and install the library:

mkdir py-spidev
cd py-spidev
wget https://raw.github.com/doceme/py-spidev/master/setup.py
wget https://raw.github.com/doceme/py-spidev/master/spidev_module.c
sudo python setup.py install

Connecting the MCP3008 to the Raspberry Pi

The eight CH0‑CH7 pins on the MCP3008 serve as analog inputs. In this example we’ll connect one of them to an LDR.

Using a Light‑Dependent Resistor (LDR)

We used an LDR EG & G Vactec, VT43, CdS, 8 Ω – 300 kΩ. In normal lighting its resistance is roughly 10 kΩ; in darkness it rises above 2 MΩ.

When light falls on the LDR, its resistance drops, pulling the voltage at the MCP3008 input toward 0 V. In the dark the resistance climbs, pushing the voltage toward the 3.3 V reference.

Any sensor that changes resistance with a physical quantity can be wired in this fashion.

Interpreting the ADC Output

The MCP3008 produces a 10‑bit number ranging from 0 to 1023, where 0 corresponds to 0 V and 1023 to 3.3 V. For an LDR, this translates to a light intensity range of approximately 0 – 10,000 lux.

These raw values can be sent to Zabbix via the Raspberry Pi’s Python script, allowing you to create dashboards, set thresholds, and trigger alerts.

For more detail: Analog Sensors Reading with Raspberry Pi and Zabbix Supervisor