Arduino SPI

Arduino SPI

You’ve heard about SPI and how it speeds up Arduino device communication. Your brain hurts every time you try to understand those four wires and odd modes. Relax! You have company. SPI appears complicated but is actually easy. This brief guide explains SPI from scratch. You’ll study SPI basics in plain English and see Arduino examples. Soon, your SPI headache will be gone. Put on your learning cap, grab an Arduino, and let’s figure out SPI!

What’s SPI?

Microcontrollers use SPI to swiftly connect with peripheral devices over short distances. One microcontroller controls numerous slave devices in a master-slave architecture.

It works. How?

SPI communicates via four wires:

  • MOSI (Master Out Slave In)—The master sends data to the slaves.
  • MISO (Master In Slave Out)—Slaves send data to the master.
  • Data transfer from the master is synchronized by the serial clock.

Master uses SS to enable a slave.

Master device controls clock and chooses slave device to interact with. Data is sent to the slave device over the MOSI line and received from the slave on the MISO line. The SCK line synchronizes data flow, enabling fast device transmission.

SPI—Why Use?

SPI has several advantages:

• Speed—SPI can carry data at up to 10 Mbps • Low pin count—Only 4 pins are needed for device connection • Simplicity—SPI is easy to install • Supported by numerous chips – Most microcontrollers and peripherals support SPI.

Common SPI peripherals:

SD cards

Gyroscopes, accelerometers, temperature sensors

OLED/TFT displays

Real-time clocks

SPI is an excellent way to quickly communicate between Arduino and other devices! Please ask me any other SPI project implementation questions.

How SPI Works

Synchronous serial interface (SPI). It has SCLK, MOSI, MISO, and SS pins. Serial clock SCLK, master out/slave in MOSI, master in/slave out MISO, and slave select SS.

The Master and Slaves

With SPI, one master controls one or more slaves. The master generates the clock signal and chooses which slave to interact with. Slaves respond to the master with data. The Arduino microcontroller is the master, while sensors, SD cards, shift registers, and more are slaves.

Sending Data

A slave is selected by driving its SS pin low by the master to transfer SPI data. The master sends one bit at a time, starting with the MSB. The master pulses SCLK and drives MOSI high or low for each bit. MOSI data is read by the slave on SCLK pulses. After sending all 8 bits, the master drives SS high to deselect the slave.

Receiving Data

Similar steps are needed to get slave data. The master chooses the slave and pulses SCLK 8 times. The slave drives MISO high or low on each pulse, and the master reads it. The master deselects the slave after 8 bits. To exchange data, master and slave switch send and receive.

Speed Up

SPI operates at rapid speeds, a benefit. Data transport is faster when SCLK frequency is increased. However, speed has limits. The maximum speed depends on your microcontroller, slave devices, and wiring quality/length. Choose the lowest frequency that matches your needs to reduce noise and other difficulties.

SPI is excellent for connecting microcontrollers and peripherals due to its simple 4-wire interface and rapid speeds. You’ll quickly interface sensors and develop data collecting systems once you get the hang of it!

Arduino SPI Pins

You must connect to Arduino’s SPI pins to use SPI. Most Arduino boards use pins 11, 12, and 13.

Master Out, Slave In—Pin 11.

Data is sent from your Arduino to the slave device via this pin. It sends the slave the desired information.

Master In, Slave Out—Pin 12

The master gets slave data via the MISO pin. Arduino receives slave device feedback through it.

Serial Clock-Pin 13

The master’s clock signal and slave-master data transfer timing are provided via the SCK pin. It synchronizes MOSI-MISO data transfer.

Slave Pin

Most SPI slaves need a slave select pin along with MOSI, MISO, and SCK. This pin lets the master enable and disable slaves. Low slave choose pin means slave is active and communicates with master. The slave is inactive when the pin is high.

Your slave device determines the slave choose pin. SS, CS, or similar abbreviations are used. For SD card modules using SPI, pin 4 is the slave select pin.

To recall, Arduino’s four major SPI pins are:

MOSI (Pin 11)—Data transfer between master and slave

Pin 12: MISO receives slave-to-master data.

Pin 13—SCK—provides clock and timing.

Enables and disables slave devices.

Four pins are all you need to communicate with SPI slave devices from Arduino! Start the data transfer.

Arduino SPI Device Connection

You must connect the slave device’s SPI pins to the Arduino SPI header to use SPI. Every slave device needs clock, MOSI, and MISO SPI pins.

MOSI: Master Out, Slave In
MOSI pins send data from the master (your Arduino) to the slave. Connect your slave device’s MOSI pin to Arduino pin 11.

The MISO pin sends slave data to the master. Connect your slave device’s MISO pin to Arduino pin 12.

A slave may have an additional Slave Select (SS) pin. The master chooses its slave device via the SS pin.Arduino code uses the SPI library to communicate with your slave device. Initialize SPI in setup():

Project Examples Using Arduino SPI

A popular Arduino SPI project involves driving an OLED display. Displays range from 0.66 to 1.5 inches and can display text, graphics, and animations. To utilize an OLED display with Arduino, connect it to the SPI bus and some control pins. The Arduino SPI library simplifies display communication.
The Weather Station
A simple weather station is another handy project. Temperature, humidity, barometric pressure, wind speed, and rainfall sensors can be connected. The Arduino reads these sensors using SPI and I2C interfaces and displays the data on an LCD or OLED screen. It can log data to an SD card for storage. Build your own weather station to learn Arduino data logging and various sensors.

mp3 player

SPI-based MP3 players are fun to make and rewarding. The VS1053 MP3 decoder can be connected to an Arduino. The Arduino sends song data and control commands to the decoder device via SPI. You’ll also need an SD card and speaker to play MP3s. You may make a rudimentary MP3 player by adding buttons.

The Digital Clock

An Arduino SPI digital clock is another simple and handy project. Connect a four-digit seven-segment display for time. With its built-in timer, the Arduino updates the display every second. SPI controls the LED segments to show the digits. Simply add a crystal oscillator for precise timekeeping. This small project teaches lots about SPI and seven-segment displays.

You can construct interesting Arduino projects using the SPI interface with a little coding and basic electronics. Endless possibilities! I hope this inspires your next Arduino project.


There you have it—a simple Arduino SPI tutorial. We covered the basics, hardware setup, and example code so you can start experimenting. The SPI protocol opens up many project possibilities if you understand it. It’s not terrifying or complicated as it seems! Get creative—blink LEDs, drive displays, read sensors. SPI is your oyster on Arduino. Be patient, start simply, and enjoy. Got it!

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