I should have added that the hardware is superfluous with a PIC, but it helps to understand what's going on. Totally bit-bangable, even by me... :) On 5/17/17, John Gardner wrote: > Check this out... > > http://merthsoft.com/linkguide/hardware.html > > On 5/17/17, Harrison Cooper wrote: >> Neil >> >> I had a similar application, where the two PICs would communicate over a >> bit >> of a distance. Undefined, but really up to 20 or 30 feet depending on ho= w >> the end user ran the cable. In my case, cost was not as much of an issu= e >> 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 >> couplers 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 cable= s >> were an unknown, 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 >> 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, bu= t >> that adds a few dollars, which is higher than I'd like. CAN transceiver= s >> 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 reduc= e >> 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 >> Western Digital Corporation (and its subsidiaries) E-mail Confidentialit= y >> Notice & Disclaimer: >> >> This e-mail and any files transmitted with it may contain confidential o= r >> legally privileged information of WDC and/or its affiliates, and are >> intended solely for the use of the individual or entity to which they ar= e >> addressed. If you are not the intended recipient, any disclosure, >> copying, >> distribution or any action taken or omitted to be taken in reliance on >> it, >> is prohibited. 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. >> >> >> -- >> 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 .