I would avoid using DTR, since it goes through a voltage converter.
As for how much you can safely draw from VCC, you are on your own... ;>
-jjf
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, May 10, 2000 2:08 PM
To: Palm Developer Forum
Subject: Powering a device from the Palm III
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/
