The other thing you get with CAN bus is common mode rejection. It's designed to tolerate as much as 50v difference. You didn't mention how the two units are to be powered, so this may or may not be of use. The other option you can consider is current loop. There's a lot of reference material for 4-20 mA current loops in industrial settings. They can be extremely reliable in some very harsh environments. -Denny On Wed, May 17, 2017 at 12:07 PM, Neil wrote: > I'm doing one-way digital communications between 2 PICs about 12 feet > apart. ~50 kHz max. Cable currently has 12V, ground, and one data > wire (5V direct from a PIC 18F output). Nothing is twisted yet -- just > straight wires. At this stage, it's functional and works fine as it is, > but I'd like to add EMI/noise immunity (against possible external noise > from other nearby signals). Shielding is noticeably increasing that > cabling cost, so I'm thinking of differential signaling instead. > Looking for a simple way to do this. > > First thought was to use RS-485 or similar differential transceivers, > but that adds a few dollars, which is higher than I'd like. CAN > transceivers are lower cost (~$0.40 each side). However, CAN is a > relatively low-level signal, so I'm thinking that I can just use 2 I/O > pins on the sender to create my own differential 5V-ish signal, and use > the comparator on the receiving PIC to process the differential signal. > I would need to add some resistors at the receiving end as the (PIC32) > comparator inputs can only handle up to 3.3V on that side. From > anyone's experience, would this even make a dent in the system's ability > to reduce noise effects? Additionally, I am hoping to have the sender > be open-drain, and pull-up at the receiver. Should this be hard-driven > to 5V instead for better noise immunity? > > Another thought is that I have 12V available at the sender, so I can use > that for the signaling level, but that adds a couple transistors. Or I > can stay open-drain at the sender and pull up to 12V at the receiver, > then voltage divide. Would it make a difference for differential > signaling? > > Thanks, > -Neil. > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .