SPI on the Raspberry Pi: Talking to a Device
Enable SPI and understand its wiring on the Pi — the same protocol from Lesson 34, now with the specific pins Raspberry Pi dedicates to it.
You'll need: an SPI device (the MCP3008 from Lesson rpi-12 works as a ready example), jumper wires, and your Pi.
Like I2C, SPI needs enabling once via sudo raspi-config → Interface Options → SPI → Enable, followed by a reboot. The Pi dedicates specific physical pins to its primary SPI bus:
| Signal | Physical pin | Role (from Lesson 34) |
|---|---|---|
| MOSI | 19 | Master out, slave in — data from the Pi to the device |
| MISO | 21 | Master in, slave out — data from the device back to the Pi |
| SCLK | 23 | Serial clock, set by the Pi |
| CE0 / CE1 | 24 / 26 | Chip-enable (chip-select) — CE0 for one device, CE1 for a second on the same bus |
Notice the Pi provides two chip-enable pins (CE0 and CE1) built directly into its SPI hardware — enough to address two SPI devices on the same bus without wiring an extra chip-select line yourself, exactly the per-device wire Lesson 34 described, just already broken out for you on the header.
In Python, the spidev library's spi.open(bus, device) call (seen in Lesson rpi-12's code) is where you choose CE0 or CE1 — spi.open(0, 0) uses CE0, spi.open(0, 1) uses CE1, letting one script talk to two different SPI devices by opening two separate connections.