Pi HATs & Accessories

The Pi's 40-pin GPIO header is also the HAT bus (I2C / SPI + ID EEPROM). The Pi 5 added a separate PCIe FPC on the bottom, which is what enables fast NVMe, AI accelerators, and modern carriers. This page covers the accessory stack; for cameras see Camera Modules; for cooling/power see Cooling & Power; for cluster carriers see Cluster Boards.

NVMe / M.2 HATs (Pi 5 only)

The Pi 5's PCIe 2.0 x1 (unofficially PCIe 3.0 with dtparam=pciex1_gen=3) finally makes NVMe legit. ~750 MB/s on Gen2, ~900 MB/s on Gen3.

• ★ Official Pi M.2 HAT+ — Pi Foundation's first-party HAT, M-key, supports 2230/2242/2260/2280; ~$12. The default if you can find it.
• ★ Pimoroni NVMe Base / NVMe Base Duo — Pi 5 underside-mount, very low profile; Duo takes two SSDs (one boot, one data, software RAID). Premium build.
• ★ Geekworm X1001 / X1003 / X1004 — popular budget HATs. X1004 is the multi-SSD variant; X1001 is single-SSD top-mount.
• Pineberry Pi HatDrive! — top and bottom variants; well-reviewed; based in Poland.
• Argon ONE V3 NVMe case — Argon's full case includes an NVMe slot underneath; see Cooling & Power.
• Waveshare PCIe-NVMe HATs — many SKUs, mid-range, generally fine.
• MakerHawk / 52Pi — budget brands; mixed reviews on PCIe FPC quality.

Watch out: cheap PCIe FPC cables are the #1 source of NVMe instability on Pi 5. Use the cable that came with the HAT, keep it short, don't reseat 50 times.

AI HATs (Pi 5)

• ★ Pi AI Kit / AI HAT+ (Hailo-8L 13 TOPS) — official Pi 5 HAT, ~$70-110. Plug-and-play with rpicam-apps. The cleanest "ML on a Pi" path. See AI SBCs.
• ★ Pi AI HAT+ (Hailo-8 26 TOPS) — newer 2024 SKU, double the TOPS, ~$110.
• Generic Hailo-8 M.2 in a Pineberry / Geekworm M.2 HAT — works but vendor blesses the AI HAT+.
• Coral USB Accelerator plugged into a Pi USB 3 port — not a HAT but the alternative ML accelerator. See AI SBCs.

PoE / PoE+ HATs

• ★ Official Pi PoE+ HAT (Pi 5) — IEEE 802.3at; powers Pi 5 with margin and includes fan; ~$30. The default.
• Official Pi PoE+ HAT (Pi 4) — same idea for the Pi 4 form factor.
• Waveshare PoE HATs — PoE (15W) and PoE+ (25W) versions; cheaper, decent.
• DSLR / Power-Splitter "PoE Texas" injectors — for "I just need 5V at the end of an Ethernet cable" without a HAT.

UPS / Power-backup HATs

• ★ PiSugar 3 / 3 Plus — LiPo-backed UPS HAT; clean shutdown on power loss; mobile-Pi staple. ~$30-50.
• Geekworm UPS HAT (X728 / X1202 for Pi 5) — 18650 cell, hot-swap; popular in Klipper/Home-Assistant always-on builds.
• Waveshare UPS HAT (B / D / E) — variants for Pi Zero / Pi 4 / Pi 5.
• Argon BLSTR / Argon EON — Argon's UPS solutions; come with full cases.

RTC

The Pi 5 finally has an on-board RTC with a battery clip on the board itself; no HAT required. For Pi 4 and earlier:

• DS3231 RTC modules — $2 from any vendor; works with i2c-rtc overlay. Long battery life.
• PCF8523-based HATs — Adafruit, Pimoroni; same I2C path.

Audio HATs

For audiophile playback (digital out → external DAC) or simple speaker-out.

• ★ HiFiBerry DAC2 HD / DAC2 Pro / Digi2 Pro — premium DAC HATs; bit-perfect output to powered speakers / external amps. Volumio and MoOdeAudio detect them automatically.
• ★ IQaudIO DAC Pro / DigiAMP+ — competitor; the DigiAMP+ has built-in 35W class-D amp for direct passive-speaker drive. Now part of Raspberry Pi Foundation since 2021.
• Pirate Audio (Pimoroni) — budget DAC + small LCD + buttons; great for small streaming boxes.
• Adafruit MAX98357 I2S Amp — bare-bones I2S to mono speaker; ~$6; for tinkering.
• JustBoom DAC / Amp — older DAC HAT vendor; still sold.

CAN-bus HATs

For Klipper Canbus toolheads, automotive diagnostics, industrial stuff.

• ★ Waveshare CAN HAT (single / dual) — cheap MCP2515-based HATs; the most common Klipper-CANbus pick.
• Seeed 2-Channel CAN-FD HAT — MCP2517FD, supports CAN-FD speeds; better for modern automotive.
• Innomaker RS485 CAN HAT — adds RS485 alongside CAN; useful for industrial.
• PiCAN3 (SK Pang) — premium CAN + RTC + SMPS HAT.

GPS / GNSS HATs

• Adafruit Ultimate GPS HAT — MTK-based, fine for general GPS.
• Sparkfun GPS-RTK2 HAT — u-blox ZED-F9P, RTK-capable for sub-cm precision.
• Waveshare LC76G / LC79D HATs — newer multi-band GNSS, cheap.

Sensor / hobby HATs

• Sense HAT v2 — gyro / accelerometer / mag / temp / humidity / pressure / 8x8 RGB LED + joystick. The classroom HAT; v2 (2024) replaced sensors with current-production parts.
• Build HAT (Pi) — drives LEGO Powered-Up motors and sensors. The Pi-Foundation-blessed LEGO bridge.
• Grove Base HAT (Seeed) — Grove ecosystem connector breakout.
• Pimoroni Inky Impression / Inky pHAT — e-paper displays.
• Pimoroni Enviro / Enviro+ — air-quality / weather sensors in a HAT.
• Adafruit Cyberdeck HAT — keyboard + screen for handheld Pi builds.

Display HATs / DSI screens

• ★ Official Pi 7" / 10" DSI Touch Display — Pi-blessed touch panel; 2024 redesign improved viewing angle. Drop-in support in Pi OS.
• Waveshare DSI / HDMI touch displays — many sizes 5" through 13.3".
• Pimoroni HyperPixel 4 — high-res DPI panel; trades GPIO pins for resolution.
• HDMI dummy plug ("ghost monitor") — not a display but worth mentioning: lets a headless Pi 5 think a monitor is attached, useful for VNC / X11 fallback.

RP1-era I/O caveats (Pi 5)

The Pi 5's south-bridge RP1 changed I2C / SPI / UART numbering and timing. Older HATs that used /dev/i2c-1 still work, but device-tree overlays may need updates. Major HAT vendors have caught up; if a 2020-era HAT misbehaves on Pi 5, check for an updated overlay.

ID EEPROM / HAT spec

The HAT spec mandates an ID EEPROM so the Pi can auto-load device-tree overlays at boot. Mature HATs all do this; cheap clones often skip it (you'll need to manually dtoverlay= in config.txt).

License / pricing reality

• The HATs themselves are hardware purchases.
• Pi Foundation HATs are reasonably priced; clone HATs from Geekworm / Waveshare / 52Pi are cheaper but quality varies — read recent reviews.
• All HAT firmware/drivers are FOSS (in-kernel) or simple dtoverlay configs.

Pick this if…

• Add fast storage to a Pi 5: Official M.2 HAT+ or Pimoroni NVMe Base.
• Add ML to a Pi 5: Pi AI HAT+ (Hailo-8L) or Coral USB.
• Power + Ethernet over one cable: Official PoE+ HAT.
• Always-on Pi, want graceful shutdown: PiSugar 3 or Geekworm UPS.
• Audiophile streamer: HiFiBerry DAC2 Pro or IQaudIO DAC Pro.
• Klipper canbus toolhead: Waveshare CAN HAT.
• GPS time / location: Adafruit Ultimate GPS HAT for general use, GPS-RTK2 for survey-grade.
• Classroom / sensors-out-of-the-box: Sense HAT v2.
• Touch panel: Official 7" DSI display; everything else is a tradeoff.