On Mon, 26 Sep 2005, alan smith wrote:

> I'm planning on using a DAA, the OEM wanted to see about using the 
> phone line power for the entire board but I'm not planning on doing 
> that now.

Here are two cheats:

1) Program the microncontroller on the board to pick up the phone and 
dial a number from time to time. The number beed not exist (or it may be 
a line that you own and never pick up. During the time the device is off 
hook you can charge the battery with the line current. The power 
available will be low. Say 10mA x 5 minutes x 12V ~= 1.6mAh per call 
(using a switcher to go down to 4.8V) (you may have to call several 
times). But this is enough to power a device that draws 30uA for 24 
hours with a 50% efficient battery.

2) Program a server to call the device's line once a day. The device 
will not answer this call. This time you have a lot more power. 10 rings 
2 seconds on each at 90Vac give 20 seconds of 0.05A which is equivalent 
to about 0.8A at 5V for 20 seconds, which is about 4.4mAh and will run a 
60uA device for 24 hours with a 50% efficient battery.

3) The off hook current must be under 500uA (better 100uA) or it will be 
flagged as a leaky line eventually. 100uA @ 40V gives 800uA of charge at 
5V, 24/7. But you will get caught.

4) If the phone company objects to this tell them to change their 
tariff. Currently a dialout that does not connect is not charged in most 
countries. This applies to 1) and 2).

I did not write this email, and the signature below is faked. The fact 
that I just got my phone bill is completely unrelated to this posting.

Peter
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist