I'm interested in the general concept of sending both power and data to a remote location (like my central heating unit does) where the remote unit is connected by a single 2-wire cable.
I've found a few links:
http://www.eetimes.com/document.asp?doc_id=1279219 http://electronicdesign.com/microcontrollers/two-wires-carry-power-and-data http://www.maximintegrated.com/app-notes/index.mvp/id/1863 http://www.eevblog.com/forum/microcontrollers/power-and-data-thru-2-wires/ http://forum.arduino.cc/index.php/topic,121868.0.html
It all looks rather complex, is there a reason why this wouldn't work, at least for sending from the local to the remote? ...
A quick test of this exact setup reveals that the remote (an Arduino Uno) is getting only 2.3V. No doubt the current-limiting resistor is responsible for that. However a more power-friendly remote, designed to use only a milliamp or so, would be more feasible. There would be less current, and therefore less voltage drop.
Or is there a fundamental flaw in this plan?
I'm thinking here that async serial, while idle, is constantly sending a HIGH bit, which therefore would power the other end, and the occasional data byte would be covered by the power stored in the capacitor.
Would it be better to move the resistor (to the other side of the diode) so it only has to regulate current for 4.3V rather than 5V?
And if you wanted to use a balanced electrical protocol, like RS485, would it be feasible to have a bridge rectifier at the remote end, to convert the balanced signal back into DC?