Google Coral Expansion Card

The Google Coral Expansion Card is a community-designed expansion card that integrates a Google Coral Edge TPU accelerator module into the Framework Laptop's expansion card form factor¹. Created by Evgeni Genchev in May 2022, the project enables on-device machine learning inference (TensorFlow Lite) through a dedicated TPU chip housed in a standard expansion card slot¹².

Background

The Google Coral Edge TPU is a small ASIC designed to accelerate TensorFlow Lite machine learning inference at the edge. It is used for computer vision, audio recognition, and other ML workloads, offering significantly better performance-per-watt than running inference on a general-purpose CPU¹³. The Coral ecosystem includes USB accelerators, M.2 modules, and bare accelerator modules (the 120-pin LGA chip used in this project)³.

Framework VP nrp (Kieran Levin) commented that a TPU expansion card had been on Framework's "wishlist of interesting projects"¹.

Design

Accelerator Module

The Google Coral Accelerator Module is a 120-pin LGA chip measuring approximately 15 mm × 10 mm¹². Despite the pin count, the design is simpler than it appears:

• 104 of the 120 pins are either 3.3V or GND
• Only 7 of the remaining 16 pins are required for basic operation via USB 2.0
• The module also supports PCIe Gen 2 x1 and USB 3.0 interfaces (the latter requiring special design considerations and Coral sales contact)¹³

PCB

Genchev designed the PCB in EasyEDA using the publicly available schematics from both Google Coral and Framework's expansion card reference designs¹². The initial version uses USB 2.0, described by Genchev as "the easiest to make into a functioning circuit"¹.

The design was completed before Genchev owned a Framework laptop — he developed it as a student unable to afford the hardware¹.

Technical Specifications

Specification	Details
TPU	Google Coral Accelerator Module (Edge TPU)3
Interface	USB 2.0 (initial design)1
Alternative Interfaces	PCIe Gen 2 x1, USB 3.0 (requires contact with Coral sales)13
Power Consumption	Up to 2 W4
Pin Count	120-pin LGA (7 active signal pins for USB 2.0)1
Module Size	~15 mm × 10 mm12
Source	EvgeniGenchev/Google-Coral-Expansion-Card (GitHub)2
Design Tool	EasyEDA2

Development Timeline

Date	Event
May 2022	Genchev announces the design and publishes PCB files on GitHub1
2022–2023	Global chip shortage prevents sourcing Coral modules; Mouser backorders estimated 6+ months out1
Feb 2023	Mouser lists 4,075 modules on order for July 2023 arrival1
May 2023	Community member chromakode successfully uses a Coral M.2 module in the Framework mainboard's WiFi slot as an alternative1
Feb 2024	Josh Cook reports successfully testing Genchev's design with a sourced module, considers build-to-order sales at $70–90 USD1

Alternative: Coral M.2 in WiFi Slot

A simpler alternative to the expansion card is installing a Coral M.2 Accelerator directly into the Framework mainboard's M.2 E-key WiFi slot¹⁴. Community member chromakode demonstrated this approach in May 2023, reporting that the single TPU M.2 module works in the WiFi slot¹.

Caveats¹⁵:

• The Framework 13 WiFi slot provides only a single PCIe x1 lane, not the dual lanes required by the dual-TPU M.2 variant
• Using the Coral M.2 displaces the WiFi module, requiring a USB WiFi adapter for wireless connectivity
• This is a trade-off between ML acceleration and internal WiFi

Use Cases

• Frigate NVR — Community member Blake Blackshear (creator of Frigate, an open-source NVR) expressed interest in using a Coral card for real-time object detection on Framework hardware¹
• On-device ML inference — TensorFlow Lite model execution for computer vision, audio classification, and keyword spotting without cloud dependency
• ML development — Local testing and iteration of edge ML models

Related Projects

• TPU Expansion Card — Earlier community discussion (November 2021) proposing a Coral TPU expansion card, which led to Genchev's design⁴
• Google Coral USB Accelerator — The commercial USB dongle version that inspired this project³
• Coral M.2 Accelerator — The M.2 module that can be used directly in the Framework WiFi slot⁵

Footnotes

1. Google Coral Expansion Card — Framework Community (Evgeni_Genchev, May 2022) ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸ ↩¹⁹ ↩²⁰ ↩²¹ ↩²²

2. EvgeniGenchev/Google-Coral-Expansion-Card — GitHub ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

3. Coral Accelerator Module — Google Coral ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

4. TPU Expansion card — Framework Community (Sri_Pramodh_Rachuri, November 2021) ↩ ↩² ↩³

5. Coral M.2 Accelerator with Dual Edge TPU — Google Coral ↩ ↩²