Note: this section is to be expanded.
phatIO is approximately 45mm long by 36mm wide
The sourcefiles for circuit and board layout are in the git repository.
When new versions of the phatIO software are written to it or extension/config (run.lio) is written to phatIO it is written to the devices’ Flash memory. This has a specified lifetime of 10,000 writes. Although phatIO attempts to minimise rewrites and actual lifetime is likely to be longer, eventually your phatIO device will not be updateable.
The maximum total power that can be consumed from the USB port is 500mA. Note, that 500mA is only available once the device has started and connected to the host computer - only 100mA is available before that. For this reason, the phatIO 5V and 3.3V pins shouldn’t be used as a general purpose power supply - extensions shouldn’t consume more than 100mA until phatIO has started and turned on any connected devices.
phatIO has a (resettable) fuse that will protect a host computer from currents exceeding the maximum - although most computers that have been tested with phatIO have been found to have built-in protection that will remove the device when it draws to much power. If this happens disconnect phatIO and all peripherals and check wiring before reconnecting.
The total power drawn from phatIO’s IO pins shouldn’t exceed 200mA in total and each pin shouldn’t exceed 40mA.
The 3.3V power rail can safely provide a few hundred mA, beyond that extra cooling may be required.
More detail to come.
Whilst phatIO is designed to be connected to a computer, it can be operated disconnected from a computer if powered with 5V through the interface socket (5V sockets on both sides of the socket are connected).
The USB and external 5V supply should NEVER be connected at the same time.
phatIO expects a smooth/regulated 5V supply.
An absolute maximum of 6V can be supplied, ideally no more than 5.5V.
A minimum of 4.5V is required to keep phatIO working within its specified tolerances. However, tests have been done down to 2.8V with phatIO starting and running (including reading the SD card). At low voltages, phatIO may not start, will not be able to power high currents, and may operate unreliably.
As well as supplying 3.3V, phatIO can be made to use 3.3V on the IO pins (with IO pins outputing 3.3V) whilst being powered from the 5V USB bus.
This is an advanced technique which requires a permanent damage to your phatIO device, make sure your phatIO device works as advertised before doing this.
Always disconnect phatIO from the USB bus before modifying the voltage.
The bottom row of connection pins (nearest the PCB) contains both the SPI and TWI buses and is intended to be used for extension boards (with driver software shipping on the phatIO filesystem)- email if you want to develop extension boards for phatIO and want to contribute to the discussion.