[Milkymist-devel] Draft 1 schematics

[Sébastien Bourdeauducq]

Hi,

On Thursday 28 January 2010 11:23:23 Adam Wang wrote:
> > What would you recommend as current limiting devices? Polyswitch?
> 
> Polyswitch is designed to protect against overcurrent. It became more
> easier everywhere. You can check [1] or [2]. Placing two PPTCs
> connected into individual usb-a connector.

What about placing one TYCO ELECTRONICS MICROSMD075F (in 1210 package) in 
series with *both* connectors ("ganged" configuration), with a current limit 
of roughly 1.5A (to allow a margin for non-compliant gadgets that use more 
than 500mA)? Looks like the simplest option to me...

> > For this purpose, we can set the drive strength of the FPGA I/O to 2mA
> > (there are no other devices on this I2C bus) which is even more efficient
> > than the 33 ohm resistors which would limit the current to 10mA and
> > requires no extra part. Of course, this assumes that the FPGA does not
> > get misconfigured with a higher drive strength.
> 
> If can let resistor value to be zero and traced to connectors as
> option if one wants to add extra device via I2C later. This could
> exempt from misconfiguration also make I2C extendable potentially.
> Some hackers may like.

For extending, I'm rather thinking of routing some spare FPGA I/Os to a 
dedicated connector. This way, adding I2C (or other) devices can be done 
without risk of interfering with the video input.

Sébastien