Neil I had a similar application, where the two PICs would communicate over a bi= t of a distance. Undefined, but really up to 20 or 30 feet depending on how= the end user ran the cable. In my case, cost was not as much of an issue = as reliability as I did not want a call saying...we are not seeing the data= all the time. I did two things to try and minimize interference and try and obtain decent= signal integrity, and that was to use CAT5 (cables are cheap...monoprice) = and ran the signals at 12V. Mine was only slave transmit to host receive, = thus I used a driver that ran it basically rail to rail, and then opto coup= lers at the other side. Systems have been in place for over 4 years..maybe= 5, and never had an issue with data loss. If your counting pennies, then = maybe its too expensive, but these were low run rate systems. The reason I= went with 12V is that it was available, and since the cables were an unkno= wn, I could also afford the IR drop along the way. -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of= Neil Sent: Wednesday, May 17, 2017 1:08 PM To: Microcontroller discussion list - Public. Subject: [EE] Low-cost differential signaling 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 di= rect 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 s= ignals). Shielding is noticeably increasing that cabling cost, so I'm thin= king of differential signaling instead. =20 Looking for a simple way to do this. First thought was to use RS-485 or similar differential transceivers, but t= hat adds a few dollars, which is higher than I'd like. CAN transceivers ar= e lower cost (~$0.40 each side). However, CAN is a relatively low-level si= gnal, so I'm thinking that I can just use 2 I/O pins on the sender to creat= e my own differential 5V-ish signal, and use the comparator on the receivin= g PIC to process the differential signal. =20 I would need to add some resistors at the receiving end as the (PIC32) comp= arator inputs can only handle up to 3.3V on that side. From anyone's exper= ience, 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 p= ull-up at the receiver. Should this be hard-driven to 5V instead for bette= r noise immunity? Another thought is that I have 12V available at the sender, so I can use th= at for the signaling level, but that adds a couple transistors. Or I can s= tay open-drain at the sender and pull up to 12V at the receiver, then volta= ge divide. Would it make a difference for differential signaling? Thanks, -Neil. -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/chang= e your membership options at http://mailman.mit.edu/mailman/listinfo/piclis= t Western Digital Corporation (and its subsidiaries) E-mail Confidentiality N= otice & Disclaimer: This e-mail and any files transmitted with it may contain confidential or l= egally privileged information of WDC and/or its affiliates, and are intende= d solely for the use of the individual or entity to which they are addresse= d. If you are not the intended recipient, any disclosure, copying, distribu= tion or any action taken or omitted to be taken in reliance on it, is prohi= bited. If you have received this e-mail in error, please notify the sender = immediately and delete the e-mail in its entirety from your system. --=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 .