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phatIO Hardware and Electrical characteristics

Note: this section is to be expanded.

phatIO is approximately 45mm long by 36mm wide

Front and back of the phatIO device. A Mini-B USB socket is used to connect the phatIO to a computer. A 28 pin socket on the other side provides access to power and IO Pins. An integrated SD card (included) contains the phatIO filesystem
Front and back of the phatIO device. A Mini-B USB socket is used to connect the phatIO to a computer. A 28 pin socket on the other side provides access to power and IO Pins. An integrated SD card (included) contains the phatIO filesystem

The sourcefiles for circuit and board layout are in the git repository.

Flash/Lifetime

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.

Power Maximums

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.

Powered Externally

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).

If the USB cable is disconnected, external power can be used to power phatIO through the 5V and GND socket pins
If the USB cable is disconnected, external power can be used to power phatIO through the 5V and GND socket pins

Important Notes:

  1. The USB and external 5V supply should NEVER be connected at the same time.

  2. phatIO expects a smooth/regulated 5V supply.

  3. An absolute maximum of 6V can be supplied, ideally no more than 5.5V.

  4. 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.

Use as 3.3V device

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.

  1. There are three pin sockets (holes) separated by 0.1" (2.54mm) on the phatIO board. When shipped the sockets towards the centre of the board are connected and the outer disconnected.
  2. On the rear of the phatIO PCB cut the trace between the two inner pin sockets as shown in the image. Ideally use a multimeter/continuity tester to check the connection both before and after cutting. Make sure you’ve completely isolated the two sockets and don’t cut any other traces
  3. Connect the other two sockets either by soldering permanently or by soldering 3 header pins in place and using a shunt to connect as shown in the image
  4. When viewed from the topside of the phatIO PCB connect the outermost pins for 3.3V operation, and the inner pins for 5.0V operation
Cut the PCB Trace between the two innermost socket pins on the rear of the phatIO PCB. Header pins and a shunt allows the device to be switched from 3.3V operation to 5V.
Cut the PCB Trace between the two innermost socket pins on the rear of the phatIO PCB. Header pins and a shunt allows the device to be switched from 3.3V operation to 5V.

Always disconnect phatIO from the USB bus before modifying the voltage.

Extension

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.

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