Yes, that's dumb of me. I'll have to think of something else... Kris At 06:32 PM 5/10/00, you wrote: >Kris, > > If the 3.3V VCC output has a 330 ohm series resistance, then you can > not get much current out of it without a significant voltage drop. > > The VCC you would get is > Vcc = 3.3V - (current draw)*330 > So for 3mA the VCC output is 2.31V. > > Also, I am not sure if the internal 3.3V regulator of the Palm is > designed to output that much current, or if the 3.3V internal voltage > would be affected. > >Jose > > >>> <[EMAIL PROTECTED]> 05/10/00 02:08PM >>> >I've asked a question about this some time in the past, in a different >context. The answers back then do not quite address my current situation. > >I have designed a small peripheral which communicates w/ the palm III >series serially via the hotsync connector. The device needs 3.0-3.5 V >supply, and usually draws only about 5 uA (standby mode). When the Palm >wants some data from the device, its serial driver comes to life, a short >burst of data gets dumped to the palm, and everything shuts back down to >the standby condition. The busy-time is about 100ms with a current draw of >maybe 2-3 mA (certainly less than 5 mA). This acquisition burst occurs >every two to ten seconds. > >Now as I noticed before, Palm formally suggests not taking any power at all >from the hotsync port. In my application, however, size is critical, and >adding even a small coin cell is difficult due to final size limitations. > >Anyway, my question is: if I want to power my peripheral from the hotsync >port, which pin might be the best to use? I see pin 2 is VCC at 3.3 V, and >pin 1 is DTR which is 3-6 V (-ish) depending on whether the serial driver >is on. Each pin is connected through a 330 Ohm R, according to the specs >(so taking as much as 10 mA from the VCC pin should be possible?). From the >looks of it, the VCC pin should be able to supply more than enough for my >application. Right? > >This type of arrangement can and has been done: TaleLight LED flashers, >GoType Keyboards, Palm's fold-out keyboard -- hey, Palm, haven't you read >your own "guidelines"? :) > >Any pitfalls(s) you can think of, apart from reducing battery life very >slightly? > >Would appreciate any words of wisdom, > >Kris Wilk >ReefNet Software >www.reefnet.on.ca > > >-- >For information on using the Palm Developer Forums, or to unsubscribe, >please see http://www.palmos.com/dev/tech/support/forums/ > > > >-- >For information on using the Palm Developer Forums, or to unsubscribe, >please see http://www.palmos.com/dev/tech/support/forums/ -- For information on using the Palm Developer Forums, or to unsubscribe, please see http://www.palmos.com/dev/tech/support/forums/
