Posted by Stef Mientki January 31, 2004
look for the FTDI232, available as bare chip or in modules.
This chip is very easy to use, because it's delivered with a number of free windows drivers.
As for the max current, normally it's limited to 100 mA,
to be able to draw  upto 500 mA,
you need 2 things extra:
- an eprom, attached to the FTDI, to tell the computer that's a high power device
- a FET to switch on the high power, after the USB chip is initialized
All schematics can be found on the FTDI site.

Stef Mientki

Dave Mucha wrote:
Hi all,
I was looking at the serial, 9 pin to USB connector cables. Seems these unit
might offer an added benefit, that is, if they work well.
It would seem that the power availabe on a USB port could be used to power some
small circuit.
>From what I have read, the USB offers about 2.5
watts of power, or up to about 500mA. Not too shabby for a simple PIC unit?
Am I on a track that might work ?
I assume I would have to modify the USB cable that I get, but at the same time,
mu current project is only a few chips....
Dave
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Posted by Michael Erath January 31, 2004

Absolutely, you’re on the right track. That 500ma 5v USB bus sole purpose is to power external circuitry.

 

Michael

-----Original Message-----
From: Dave Mucha [mailto:d...@juno.com]
Sent: January 31, 2004 01:54 PM
To: p...@yahoogroups.com
Subject: [piclist] USB to Serial ?

 

Hi all,

I was looking at the serial, 9 pin to USB connector cables.  Seems
these unit might offer an added benefit, that is, if they work well.

It would seem that the power availabe on a USB port could be used to
power some small circuit.

From what I have read, the USB offers about 2.5 watts of power, or up
to about 500mA.  Not too shabby for a simple PIC unit?

Am I on a track that might work ?

I assume I would have to modify the USB cable that I get, but at the
same time, mu current project is only a few chips....

Dave


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Posted by Dave Mucha January 31, 2004
Hi all,

I was looking at the serial, 9 pin to USB connector cables. Seems
these unit might offer an added benefit, that is, if they work well.

It would seem that the power availabe on a USB port could be used to
power some small circuit.

From what I have read, the USB offers about 2.5 watts of power, or up
to about 500mA. Not too shabby for a simple PIC unit?

Am I on a track that might work ?

I assume I would have to modify the USB cable that I get, but at the
same time, mu current project is only a few chips....

Dave