You could RF couple it....? Gnite All, JJ -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Ben Jackson Sent: Tuesday, 13 January 2004 10:43 PM To: PICLIST@MITVMA.MIT.EDU Subject: [EE]: One wire serial between devices with no common ground I'd like to have a serial (one way would be okay, two way better) interface between two PICs with different power supplies. One would probably be on a regulator powered by a wall wart and the other would be battery powered. The battery powered device will be on a rotating platform, so I'd like to connect just through the metal axle it's rotating on. I'm a software guy, not an EE guy, so if this idea is stupid for some obvious reason, please enlighten me. Here's my circuit (one half, one for each side): VCC + TX R1_ | o----|___|----|-----. 100 | | | | C1 \| | || WIRE Q1 |---o--||---o <| || RX | 1uF o-------------o | .-. 1k | |R2 | | '-' | === GND Q1 acts as an envelope detector and provides a logic level signal to RX. TX is high-Z when receiving. When transmitting, RX sees what got sent and the 'slave' device can release the line if it sees an error. TX needs to be driven without a DC component, which can probably be done by manchester encoding bytes before sending them via the UART (start/stop are already balanced). It might be necessary after a quiescent period to drive 0xAA (or 0x55) to frame the message and 'balance' the line. -- Ben Jackson http://www.ben.com/ -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics