On Sun, 26 Apr 2009 22:23:45 -0400 solarwind wrote: > One possible solution is to network over wireless, but this is very > expensive when I have 5 or 6 units to interconnect. Another Idea is > through the telephone line. How would I modulate signals over the > telephone line? The aim of the circuit design is that it should be > simple. If speed isn't a problem, check for 300 Baud modem chips. They were used in fax machines and are cheap. TCM3105 used to be a popular one, but isn't manufactured anymore. DB614 is a more modern one (not too modern though ;-) I'm quite afraid of using over-the-mains communications, and it's complicated. Look for X10 circuits. There are sites with all the circuitry. X10 only transmits during zero crossing to avoid the interference on the line. John -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist