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 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 dece= nt > 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 system= s. > The reason I went with 12V is that it was available, and since the cables > 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 apa= rt. > ~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 l= ike > to add EMI/noise immunity (against possible external noise from other nea= rby > 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-leve= l > 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-drai= n, > and pull-up at the receiver. Should this be hard-driven to 5V instead fo= r > 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 c= an > 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/cha= nge > your membership options at http://mailman.mit.edu/mailman/listinfo/piclis= t > Western Digital Corporation (and its subsidiaries) E-mail Confidentiality > Notice & Disclaimer: > > This e-mail and any files transmitted with it may contain confidential or > legally privileged information of WDC and/or its affiliates, and are > intended solely for the use of the individual or entity to which they are > 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 t= he > 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 .