USB modules take 0.9 amps peak, and 0.5 amps typical. That is 2.5 watts typical.

The Coral Dev Board single-board computer with Edge TPU specifies a USB-C source with up to 3A, that's 15W or as much as my first soldering iron. The heatsink and fan are rated at 0.65 watts, so I don't know where the rest of it is going. Maybe it has a high inrush current.

It looks similar to the R-Pi. 85 x 56 mm is the same bank-card size. The mounting holes are on the corners of a 49 x 58 mm rectangle for the R-Pi.

The header pinout has the power and ground positions as the R-Pi.

Pins 27 and 28 are I2C SDA and SCL, where they are reserved (DNC) on the R-Pi.

So I'd cautiously say this is not a coincidence, and that they intended it to be compatible in order to make interfacing easy. You must check this for yourself!

The chipset is not the Broadcom device used in the Pi, but a similar sort of thing. CPU, GPU, and VPU.

It has something the Pi does not: a Microchip ATECC608A cryptographic coprocessor. It is a small (SOIC) 8-pin chip, so not a massive power drain.

I expect the advantage of having the TPU integrated on the board is that it avoids the overhead of USB traffic. You even get a pair of TPUs on a Mini PCIe or M.2 cards that can fit in laptops.

2023-04-08

The get-started guide is here: https://coral.ai/docs/dev-board/get-started/

It was fairly easy to follow. It does not boot the OS from an SD card (as the Raspberry Pi does), but stores it on-board. To get it there, you can load it either from an SD card or a serial port.

I avoided faffing around making an SD card (which would only be needed once), and loaded it from the serial port. You need to jump ahead to here: https://coral.ai/docs/dev-board/reflash/#first-time-setup then jump back to get-started.

The board is also designed to run "headless" - you talk to it via the serial port instead of needing a keyboard, mouse and monitor. There is an HDMI video output, but this is meant for showing processed video, not a user interface.

The parrot image recognition demo runs about the same speed as TPU USB dongle.

The vehicle video recognition demo recognises cars and trucks in a record video of motorway traffic. It can display the results through either the HDMI port or an internet browser window. You can press 'n' to see the performance difference between using the microprocessor (about 3 frames per second) or the TPU (about 74 frames per second). 

I notice the fan is not on all the time, and I assume this is to conserve fan life by only running when the TPU is busy.

There are some interesting example projects, such as a bird feeder that recognises squirrels trying to steal bird food!

https://coral.ai/projects/bird-feeder/

2023-04-09

Having got it up and running, eventually it will need some video input. The camera connections are not compatible with the Raspberry Pi camera module, but the Coral camera is only about $20. Unfortunately everywhere is out of stock at this moment.

2023-04-15

I bought a case for £22 which turned out to be two rather flimsy (1 mm thin aluminium) bits of punched and folded metal, held together by slots in the top and tabs on the bottom. The slots are bigger than the tabs, so top will rattle if you shake the bottom. The micro-SD slot just about lines up with the socket if you pull the top upwards. Due to the looseness of the tabs, if you put a card in and press the top of the case, the top will press on the card and damage the card or push the socket off the PCB. This could be fixed by filing the slot wider. It will then merge with the headphone socket hole, which is probably what the designers were trying to avoid. The sides of the top have to bend out to get over the headphone/USB-C/HDMI connectors, take care not to bend it beyond its elastic limit. 

A bit disappointing quality but it does the job of protecting the board from finger-borne electrostatic discharge, and from drops IF the micro SD slot is filed bigger.

2023-04-26

SD slot filed bigger.